Diagnosis and management of acyanotic heart disease: Part II - left-to-right shunt lesions
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《美国医学杂志》
Division of Pediatric Cardiology, University of Texas-Houston Medical School, Childrens Heart Institute, Memorial Hermann Childrens Hospital, Houston, Texas, USA
Abstract
In this review, the clinical features and management of most commonly encountered acyanotic, left-to-right shunt lesions are discussed. Patients with small defects, especially in childhood, are usually asymptomatic while moderate to large defects in infancy may present with symptoms. Hyperdynamic precordium, widely split and fixed second heart sound, ejection systolic murmur at the left upper sternal border and a mid-diastolic flow rumble at the left lower sternal border are present in atrial septal defects, holosystolic murmur at the left lower border is characteristic for a ventricular septal defect whereas a continuous murmur at the left upper sternal border is distinctive for patent ductus arteriosus. Clinical diagnosis is not usually difficult and the diagnosis can be confirmed and quantitiated by non-invasive echocardiographic studies. Whereas surgical intervention was used in the past, transcatheter methods are increasingly used for closure of atrial septal defect and patent ductus arteriosus. Small ventricular septal defects may not need to be closed whereas medium and large defects may require surgical closure. Transcatheter closure of both muscular and membranous ventricular septal defects is feasible by transcatheter methodology, but these techniques are experimental at the time of this writing.
Keywords: Atrial septal defect; Ventricular septal defect; Patent ductus arteriosus; Transcatheter closure
As alluded to in the preceding paper, congenital heart defects (CHDs) may be classified into acyanotic and cyanotic, depending upon whether the patients clinically exhibit cyanosis. The acyanotic defects may further be subdivided into obstructive lesions and left-to-right shunt lesions. The obstructive lesions have been reviewed in the preceding paper. In this paper important findings in history, physical examination and laboratory studies that are suggestive of the diagnosis of the respective left-to-right shunt lesion and the available options in the management of these defects will be reviewed.
LEFT-TO-RIGHT SHUNT
When there is a defect in the partition between left and right heart structures, the oxygenated blood is shunted from left-to-right because of generally lower pressure and/or resistance in the right heart than in the left. The physical findings are either a manifestation of flow across the defects or due to effects of excessive flow across the cardiac chambers (volume overload) and valves or both. The magnitude of the shunt determines the clinical presentation and symptoms.
Atrial Septal Defect
There are three major types of atrial septal defects (ASDs) and these include ostium secundum, ostium primum and sinus venosus defects. The clinical features are essentially similar but I will mainly concentrate on ostium secundum ASDs. Atrial septal defects constitute 8% to 13% of all CHDs.[1] Pathologically, there is deficiency of the septal tissue in the region of fossa ovalis. The defects may be small to large. Most of the time, these are single defects, although, occasionally multiple defects and fenestrated defects can also be seen. Because of left-to-right shunting across the defects, the right atrium and right ventricle are dilated and somewhat hypertrophied. Similarly, main and branch pulmonary arteries are also enlarged. Pulmonary vascular obstructive changes are not usually seen until adulthood.
Symptoms : Isolated ASD patients are usually asymptomatic and are typically detected at the time of preschool physical examination. Sometimes these defects are detected when echocardiographic studies are performed for some unrelated reason. A few patients do present with heart failure in infancy, although this is uncommon.
Physical Examination: The right ventricular and right ventricular outflow tract impulses are increased and hyperdynamic. No thrills are usually felt. The second heart sound is widely split and fixed (splitting does not vary with respiration) and is the most characteristic sign of ASD. Ejection systolic clicks are rare with ASDs. An ejection systolic murmur is heard best at left upper sternal border; it is soft and is of grade II-III/VI intensity and rarely, if ever, louder. The murmur is secondary to increased flow across the pulmonary valve. A grade I-II/VI mid-diastolic flow rumble is heard (with the bell of the stethoscope) best at the left lower sternal border. This is due to large volume flow across the tricuspid valve. There is no audible murmur because of flow across the ASD.
Noninvasive Evaluation: Chest X-ray usually reveals mild to moderate cardiomegaly, prominent main pulmonary artery segment and increased pulmonary vascular markings Figure1. The electrocardiogram shows mild right ventricular hypertrophy; the so-called diastolic volume overload pattern with rSR' pattern in the right chest leads Figure2. Echocardiogram reveals enlarged right ventricle with paradoxical septal motion, particularly well-demonstrable on M-mode echocardiograms Figure3. By two-dimensional echocardiogram, the defect can be clearly visualized Figure3 and 4). The type of ASD, secundum Figure3 & Figure4 versus primum Figure5 can also be delineated by the echocardiographic study. Sinus venosus defects may escape detection and should be specifically looked for. Apical and precordial views may show "septal drop-outs" without an ASD because of thin-ness of the septum in the region of fossa ovalis. Therefore, subcostal views should he scrutinized for evidence of ASD. In addition, demonstration of flow across the defect with pulsed Doppler Figure6 and color Doppler echocardiography (not shown) is necessary to avid false positive studies.
Catheterization and Angiography: Clinical and echocardiographic features are sufficiently characteristic so that cardiac catheterization is not necessary for diagnosis. However, cardiac catheterization is an integral part of transcatheter occlusion of ASD.
When catheterization is performed, one will observe step-up in oxygen saturation at the right atrial level. The pulmonary venous, left atrial, left ventricular and aortic saturations are within normal range. In large defects, the pressures in both atria are equal while in small defects, an interatrial pressure difference is noted. The right ventricular and pulmonary arterial pressures are usually normal. Calculated pulmonary-to-systemic flow ratio (Qp:Qs) is used to quantitative the degree of shunting and a Qp:Qs in excess of 1.5:1 is considered an indication for closure of ASD.
Selective angiography in the right upper pulmonary vein at its junction with the left atrium in a four-chamber view will reveal location and the size of the ASD. When anomalous pulmonary venous connection is suspected, selective left or right pulmonary arterial angiography should be performed and the levophase of angiogram should be scrutinized for anomalous connections.
To avoid missing a diagnosis of partial anomalous pulmonary venous return, we usually perform a number of routine maneuvers and these include (i). Measurement of oxygen saturations from both right and left innominate veins at the time of superior vena caval sampling, (ii). Left innominate vein cineangiogram in posterior-anterior view with diluted contrast material, (iii). Probe for all the four pulmonary veins from the left atrium and (iv) . As mentioned before, obtain cineangiography from the right upper pulmonary vein at its junction with the left atrium in a left axial oblique (300 LAO and 300 cranial) view.
Management. Despite lack of symptoms at presentation, closure of the ASD is recommended so as to (i) prevent development of pulmonary vascular obstructive disease later in life, (ii) reduce probability for development of supraventricular arrhythmias and (iii) prevent symptoms during adolescence and adulthood. Elective closure around age 4 to 5 years is recommended. Closure during infancy is not undertaken unless the infant is symptomatic. Right ventricular volume overloading by echocardiogram and a Qp:Qs >1.5 (if the child had cardiac catheterization) are indications for closure.
The conventional treatment of choice is surgical correction. While the secundum ASDs can be successfully repaired by open-heart surgical techniques with a low (<1%) mortality, the morbidity with cardiac surgery is universal, and residual scar is present in all. Because of this reason several transcatheter methods have been developed.[2],[3] Clinical trials have been undertaken with a large number of devices as reviewed elsewhere[4],[5] and feasibility, safety and effectiveness of these devices in occluding the ASD have been demonstrated. Some of the devices have been discontinued and others modified and redesigned.[2],[3],[4],[5] At the present time, only one device, the Amplatzer Septal Occluder, is approved for general clinical use by the US Food and Drug Administration (FDA). A number of other devices are in FDA-approved (under Investigational Device Exemption) clinical trials with local IRB supervision. These devices, to the best of my knowledge, are CardioSeal/StarFlex, Helex device and transcatheter patch.
The Amplatzer Septal Occluder is rapidly becoming the device of choice because of ease with which the device can be implanted, retrieved and repositioned plus the comfort that the device is FDA approved. The procedure involves percutaneous right heart catheterization to confirm the clinical and echocardiographic diagnosis with particular attention to exclude partial anomalous pulmonary venous return. A left atrial cineangiogram in a left axial oblique view (300 LAO and 300 Cranial) with the catheter positioned in the right upper pulmonary vein at its junction with the left atrium is then performed. This is followed by transesophageal or intracardiac echocardiography to measure the size of the ASD, to visualize entry of all pulmonary veins into the left atrium and to examine the atrial septal rims. Static balloon sizing of the ASD using NuMed PTS or AGA Amplatzer sizing balloons should follow. During balloon occlusion, color Doppler evaluation of the atrial septum to rule out additional atrial defects should be carried out. An Amplatzer Septal Occluder that is 1 to 2 mm larger than the stretched diameter of the ASD is selected for implantation. The size of delivery sheath accommodating the selected device should then be positioned in the left upper pulmonary vein, taking appropriate precautions to avoid inadvertent air entry into the system. The selected device is screwed onto the delivery cable, the device is loosened by unscrewing by one turn and drawn into the loader sheath under saline. The device is deposited into the delivery sheath while flushing the loader sheath continuously with saline or a similar flushing solution. This is to prevent inadvertent air entry into the system. The device is advanced within the sheath under fluoroscopic guidance until it reaches the tip of the delivery sheath in the left upper pulmonary vein. It is important not to rotate the delivery cable to prevent inadvertent unscrewing of the device. The entire system is withdrawn until the tip of the sheath slips into the free left atrium and the device advanced, thus releasing the left atrial disk. Under echocardiographic guidance, the entire system is withdrawn such that the left atrial disk is flush against the left atrial side of the atrial septum occluding the ASD. Then, while the device cable is held steady, the delivery sheath is withdrawn releasing the waist of the device within the atrial septal defect, followed by further withdrawal of the sheath deploying the right atrial disk in the right atrium. The position of the device is verified by echocardiography and residual shunt looked for. If the device position is satisfactory, the device cable is moved back and forth (so called Minnesota Wiggle) and the device cable is rotated counterclockwise, releasing the device. If the device position is unsatisfactory, the device can be withdrawn into the sheath and redeployed. A repeat echocardiography to ensure good position of the device is undertaken. Right atrial cineangiography through the delivery sheath is performed by some cardiologists prior to withdrawal of the delivery sheath out of body. Arterial line to monitor the systemic pressures throughout the procedure, administration of heparin (100 units/kg) and monitoring the ACT to keep it above 200 seconds, and administration of Ancef or a similar antibiotic are routine parts of the procedure. Aspirin 5 mg/kg as a single daily dose for six months is usually recommended. Large defects, small septal rims, multiple defects and septal aneurysms pose additional problems and appropriate adjustments in the technique[6] should be undertaken to ensure success of the device implantation.
Both immediate and mid-term follow-up results of Amplatzer Septal Occluder appear excellent with immediate complete closure rates varying from 62% to 96% which improved to 83% to 99% at six to 12 month follow-up.[7] We undertook closure of 31 ostium secundum defects with this device; there was a small residual shunt in one patient at the conclusion of the procedure. This shunt disappeared at one month follow-up. No residual shunts observed during a mean follow-up of 12 months.
Ostium primum and sinus venosus defects are not amenable to transcatheter closure and surgical correction is the treatment of choice. Also, secundum defects not amenable to transcatheter closure are candidates for surgical closure. Surgery is usually performed under cardiopulmonary bypass and sternotomy. In the ostium primum defect, apart from closing the ASD, the mitral valve should be repaired in such a manner as to preserve its function. In sinus venosus defect, diversion of the anomalously connected right pulmonary vein(s) into the left atrium along with the closure of the ASD should be undertaken.
Ventricular Septal Defect
Ventricular septal defect (VSD) is the most common CHD and constitutes 20% to 25% of all CHDs.[1] The VSD may be small, medium or large and is classified based on its location in the interventricular septum. The defect is most commonly (80%) located in the membranous septum, in the subaortic region and is commonly referred to as perimembranous defect. The defect may also be located in the conal septum in the sub-pulmonary region and is called supracrystal defect and constitutes 5% to 7% of VSDs. This type of defect is more commonly encountered in the Far East including Japan and there it may constitute up to 29% of VSDs. The third type, in the posterior septum, is commonly referred to as atrioventricular canal defect and approximately 8% of the VSDs are of this type. Finally, the defect may be located in the muscular and apical portion of the ventricular septum and may make-up 5% to 20% of all VSDs. When multiple muscular defects are seen, it is often referred to as "Swiss-cheese" type of VSD.
Symptoms: The clinical symptomatology is largely dependent upon the size of the VSD. In small defects, the patients are usually asymptomatic and are detected because a cardiac murmur heard on routine examination. Patients with medium and large defects may present with symptoms of congestive heart failure (dyspnea, tachypnea, sweating and failure to gain weight) or with symptoms related to bronchial obstruction and/or respiratory infection.
Physical Findings: These, again, depend upon the size of the defect. In small defects the only abnormality is a loud holosystolic murmur Figure7 heard best at the left lower sternal border. When the VDS is small, the murmur is loud and is sometimes referred to as "maladie de Roger". Sometimes, the holosystolic murmur may be heard best at left mid and left upper sternal borders, depending upon the direction of the VSD jet. In very small defects, the murmur, though begins with first heart sound, may not last through the entire systole; the shorter the murmur, the smaller is the defect.
In medium and large defects, the right and left ventricular impulses are increased and somewhat hyperdynamic. A thrill may be felt at the left lower sternal border. The second heart sound is split unless there is pulmonary vascular obstructive disease, in which case a loud single second heart sound is heard. The pulmonary component of the second sound may be normal or increased, depending upon the degree of elevation pulmonary artery pressure. Clicks are unusual for VSD patients although they can be heard in patients whose VSDs are undergoing spontaneous closure by aneurismal formation of the membranous ventricular septum. A holosystolic murmur is best heard at the left lower sternal border and does not usually radiate although it may be widely heard over the precordium. The intensity of the murmur may vary between grade II-V/Vl. There is no significant variation of this murmur with respiration. This murmur is produced by flow across the VSD. The intensity of the murmur does not bear any consistent relationship with the size of the defect. A grade I-II/Vl mid-diastolic flow rumble may be heard at the apex in patients with medium to large-sized defects and large left-to-right shunts; this murmur is heard best with the bell of' the stethoscope. The mid diastolic murmur is due to increased flow across the mitral valve and usually indicates a Qp:Qs greater than 2:1.
Noninvasive Evaluation: Chest X-ray shows cardiomegaly and increased pulmonary vascular markings if the shunt is large. Left atrial enlargement may be noted. The electrocardiogram may be normal in very small defects or may show evidence for left ventricular hypertrophy in small to moderate defects while it may show biventricular or right ventricular hypertrophy in moderate to large defects. Electrocardiographic signs of left atrial enlargement may also be seen. Severe right ventricular hypertrophy may be seen if pulmonary vascular obstructive disease develops.
Echocardiogram shows increase in left atrial and left ventricular size, which is again dependent upon the size of the VSD. The location and size of the VSD can be imaged by 2-dimensional echocardiography Figure8 and Figure9. Left-to-right shunting across the VSD can be demonstrated by Doppler echocardiography (not shown). Peak Doppler flow velocity magnitude is inversely proportional to the size of defect. Indeed the right ventricular/pulmonary arterial pressures may be estimated by determining to peak Doppler flow velocity across the VSD.
RV/PA peak pressure = peak arm blood pressure - 4 VVSD2
where RV and PA are right ventricle and Pulmonary artery and VVSD is the peak Doppler velocity across the VSD.
The right ventricular peak pressure may also be estimated by tricuspid back flow (regurgitant) velocity:
RV peak pressure = 4 VTR2 + RAP
where VTR is peak tricuspid regurgitant velocity and RAP is estimated right atrial pressure (5 mmHg).
Both formulas may help to verify internal consistency of the Doppler methodology in estimating the size of the VSD. The higher the estimated RV pressure, larger is the size of the VSD.
Cardiac Catheterization & Cineangiography: Many of the issues that required definition by catheterization in the past can be resolved by good quality echo-Doppler studies and catheterization is not routinely required. When questions cannot be satisfactorily answered, cardiac catheterization may be useful.
Step-up in oxygen saturation is observed in the right ventricle. The saturations in the left-side of the heart are usually normal. The right ventricular and pulmonary arterial pressures are normal in small VSDs and are elevated in moderate to large defects; the magnitude of elevation is proportional to the size of the VSD. Calculated Qp:Qs gives an estimate of degree of left-to-right shunting. A Qp:Qs greater than 2:1 is generally considered an indication for intervention. Pulmonary vascular resistance may be calculated:
Mean PA presence - Mean LA pressure
PVR =
Pulmonary blood flow index
where PVR is pulmonary vascular resistance, PA and LA are pulmonary artery and left atrium respectively.
The calculated resistance is usually 1 to 2 units and a resistance in excess of 3.0 units is considered elevated. Marked elevation of the resistance (>8.0 units) contraindicates surgical repair. When the resistance is elevated, oxygen and other vasodilating agents should be administered to demonstrate the reversibility.
Selective left ventricular angiography in a left axial oblique view is usually required to demonstrate size and location of the VSD. Examples of a perimembranous and a muscular VSD are shown in [Figure - 10].
Natural History of VSDs: Knowledge of the natural history of these defects is interesting and such understanding is important in the management of these defects: (i) Spontaneous closure. Approximately 40% of VSDs spontaneously and completely close. Additional 25% to 30% of defects may become small enough not to require surgical intervention. While small defects tend to close more frequently than large defects (60% vs 20%), even defects large enough to produce congestive heart failure or require pulmonary artery banding in infancy go on to close spontaneously. The majority of the defects close by age 2, most close by age 5 to 7 years, but the process of spontaneous closure continues through adolescence and adulthood. Most commonly the defect closes by apposition of leaflets of the tricuspid valve against it or by aneurismal formation of the membranous ventricular septum. (ii) Pulmonary vascular obstructive disease may develop in 10% of VSDs. This is probably related to the exposure of the pulmonary vascular bed to high pressure and high flow. Prompt diagnosis and closure of the defect at least prior to 18 months of age is likely to reduce the incidence of development of pulmonary vascular disease, (iii) Development of infundibular stenosis, the so called Gasul's transformation of the VSD may occur in 8% of the defects. There may be specific markers such as right aortic arch and increased angle of the right ventricular outflow tract that may predispose a VSD to undergo Gasul's transformation. While development of infundibular stenosis eventually requires the patient to have surgery, it indeed protects the pulmonary vascular bed and prevents development of pulmonary vascular obstructive disease. (iv) Aortic insufficiency develops in approximately 5% of patients. This may either be related to prolapse of an aortic valve cusp into the VSD or lack of support to the aortic root. This complication appears to occur more commonly with supracrystal VSDs than with other types. Surgical correction is indicated if moderate to severe aortic insufficiency is present.
Management: The management strategies depend, to a large degree, on the size of the VSD. In small VSDs reassurance of the parents, subacute bacterial endocarditis prophylaxis and periodic clinical follow-up are all that are necessary. In moderate-sized defects, treatment of heart failure, if present, should be undertaken. Failure to thrive and markedly enlarged left ventricle are probably indications for surgical closure. In very large defects the heart failure should be treated aggressively. If the congestive heart failure is difficult to control with the usual anticongestive measures or if failure to thrive is present, surgical closure should be undertaken.
In large defects with near systemic pressures in the right ventricle and pulmonary artery, surgical closure should be performed prior to 18 to 24 months of age even if heart failure control and adequate weight gain are present. Total surgical correction is currently recommended. The previously used approach of initial pulmonary artery banding in small and young babies followed by surgical closure of the VSD later is no longer recommended. However, in muscular, Swiss-cheese variety of defects, initial pulmonary artery banding may be appropriate.
When the pulmonary vascular resistance is elevated, its response to oxygen and other vasodilator agents, pulmonary arterial wedge angiography and sometimes, even lung biopsy may be necessary to determine the suitability for surgical closure. Patients with calculated pulmonary vascular resistance less than 8 wood units with a Qp:Qs >1.5 are generally considered suitable candidates for surgery. If the resistance drops to levels below 8 units after administering oxygen or other vasodilator agents, the patient becomes a candidate for surgery.
Large VSDs with severe elevation of pulmonary resistance (irreversible pulmonary vascular obstructive disease) are not candidates for surgery. Symptomatic treatment and erythropheresis for symptoms of polycthemia should be undertaken. These patients may eventually become candidates for lung transplantation.
When surgery is indicated, open heart surgical technique is the treatment of choice. Some workers have attempted transcatheter occlusion of VSD in a manner similar ASD closure; a number of devices have been used for this purpose and include, Rashkind's double-umbrella, clamshell device, buttoned device, Amplatzer device, CardioSeal/StarFlex, and Nit-occlud.[8] Such method may be feasible in muscular defects and membranous defects with sufficient septum in the subaortic region so that the device can be implanted without interfering with aortic valve function. To circumvent this problem, the Amplatzer device was redesigned[9] such that the aortic end of the left ventricular disc is short (0.5 mm) while the opposite end is longer (5.5 mm). A platinum marker, to indicate the lower pole of the left ventricular disc, is built into the system and should be appropriately positioned during the device delivery and implantation. This modified device was used in children with small to medium-sized VSDs[9] and the results were good. Further experience with this device is necessary prior to its widespread use. At the present, transcatheter VSD occlusion is considered experimental.
Patent Ductus Arteriosus
Ductus arteriosus is one of the fetal circulatory pathways which diverts the desaturated blood from the main pulmonary artery into the descending aorta and placenta for oxygenation. After the infant is born, the ductus arteriosus constricts and closes spontaneously, presumably secondary to increased PO2. But in some children, such spontaneous closure does not occur. This is more frequent in prematurely born infants. Patent ductus arteriosus (PDA) may be an isolated lesion and may be present in association with other defects. Isolated PDA constitutes 6 to 11% of all CHDs.[1] In this section, isolated PDA beyond neonatal (and premature) period will be discussed. PDA is a muscular structure connecting the main pulmonary artery (at its junction with the left pulmonary artery) with the descending aorta at the level of left subclavian artery. The configuration of PDA varies considerably but most often it has a conical or funnel shape. The aortic end is wide and gradually narrows (ampulla) towards the pulmonary end. The narrowest segment is at the pulmonary end. Other types which are short and tubular and those with multiple constrictions and bizarre configuration can also be seen.[10] Because of usually higher pressure and resistance in the systemic circuit than in the pulmonary circuit, left-to-right shunt takes place across the PDA. The magnitude of left-to-right shunting depends upon the diameter of the ductus and ratio of pulmonary to systemic vascular resistance.
Symptoms: Clinical presentation depends upon the size of the ductus. If the PDA is small, there are no symptoms and it is usually detected because of a murmur detected on a routine examination. Moderate to large ductus with large shunt may either present with symptoms of easy fatigability, symptoms associated congestive heart failure or respiratory symptoms suggestive of lung collapse (very large ductus in small babies).
Physical Findings: Left ventricular impulse may be hyperdynamic with large shunts. A thrill may be felt at the left upper sternal border and in the suprasternal notch. The first heart sound is usually normal and the second heart sound may be buried within the murmur. In the majority of cases, a continuous murmur [Figure - 11] is heard best at the left upper sternal border. The murmur begins in systole and continues through the second heart sound into the diastole. The systolic component of the murmur crescendos up to the second heart sound while the diastolic part descrescendos to a varying distance (time) into the diastole. The continuous murmur must be distinguished from the to-and-fro murmur; the latter is a combination of an ejection systolic murmur and an early diastolic descrescendo murmur (for example aortic stenosis and insufficiency) and there is a definite gap between the end of the ejection murmur and the second heart sound, while no such gap is auscultated with continuous murmurs [Figure - 11]. The continuous murmur of PDA may be of grade I-V/VI in intensity. There is some beat-to-beat variation in the intensity of the murmur and for this reason it is described as machinery murmur. Multiple ejection clicks are usually heard within the murmur and this is rather characteristic of the PDA. The majority of the time, the murmur does not change with the position of the body, although the diastolic component of the murmur is heard better in a supine than in an upright position. However, in patients with very small PDA, the continuous murmur of the PDA either completely disappears or becomes only systolic in timing when the patient sits up and returns to continuous quality when the patient assumes supine position. The postulated cause of this is "kinking" of the ductus in the upright position.[11] When the ductus is moderate to large in size, a mid-diastolic murmur may be heard at the apex because of increased flow across the mitral valve, such a mid-diastolic murmur suggests a Qp:Qs greater than 2:1. Arterial pulses are bounding in all but patients with very small ductus.
Noninvasive Evaluation: Chest X-ray may show a normal-sized heart with normal pulmonary vascular markings with small ductus while cardiomegaly, increased pulmonary blood flow and left atrial enlargement may be seen with moderate to large ductus. Collapse with secondary inflammatory process may be observed in the lung fields of small children with large ductus. The electrocardiogram may be normal or may show left atrial and left ventricular enlargement, depending upon the size of the ductus. Biventricular hypertrophy may be seen large ductus and right ventricular hypertrophy in patients with pulmonary vascular obstructive disease.
Echocardiogram may reveal varying degrees of left atrial and left ventricular enlargement, again depending upon the size of the ductus. The left ventricular contraction indices are normal to elevated unless severe myocardial dysfunction sets in. Doppler echocardiography shows characteristic diastolic flow pattern in the pulmonary artery [Figure - 12], indicative of PDA. Characteristic color flow mapping distribution (not shown) is also present.
Cardiac Catheterization and Selective Cine Angiography: These invasive studies are not necessary in the usual cases of PDA, although these procedures are integral parts of transcatheter closure.
Oxygen saturation data show a step up in oxygen saturation at the pulmonary artery level. The left heart saturations are usually normal. Calculated Qp:Qs, though usually indicates degree of shunting, it may not be accurate because of the difficulty in obtaining reliable mixed pulmonary arterial saturations. The right ventricular and pulmonary arterial pressures are normal in patients with small PDA but may be elevated if the PDA is moderate or large. Wide pulse pressure is observed in the aorta.
Selective aortic arch angiogram demonstrates the size, shape and location of the ductus and are demonstrated in [Figure - 13].
Management: It is generally believed that the presence of an isolated ductus is an indication for closure, mainly to prevent bacterial endocarditis. This can be performed at anytime, especially if associated with heart failure or pulmonary compromise. If the patient is asymptomatic, waiting until 6 to 12 months of age is generally recommended. Since the description of successful surgical ligation of patent ductus arteriosus by Gross and Hubbard in 1939, surgery has been extensively used in the treatment of PDA and has become the treatment of choice. The procedure involves thoracotomy under general anesthesia and ductal ligation or ligation and division, as per the surgeon's preference. While the risk of surgical closure is low, morbidity associated with it, namely anesthesia, endotracheal intubation and thoracotomy is universal. Because of this reason, less invasive, transcatheter closure techniques have been developed.[12] These transcatheter methods are increasingly being used in closing PDAs. A number of PDA occluding devices have been designed and investigated in human clinical trials as reviewed elsewhere;[13],[14] and include Ivalon foam plug, polyurethane foam covered single umbrella with miniature hooks, Rashkind PDA occluder system, Botallo-occluder, adjustable buttoned device, clamshell ASD device, Gianturco Coil, duct-occlude pfm, Cook detachable coil, flipper detachable coil, Gianturco-Grifka Vascular Occlusion Device (GGVOD), infant buttoned device, polyvinyl alcohol foam plug, Amplatzer duct-occluder, folding plug buttoned device, and wireless PDA devices. Gianturco coils (both free and detachable), GGVOD and Amplatzer duct occluder are currently available for routine clinical use. The remaining devices, at the time of this writing, have not received approval from the appropriate regulatory authority, but are available for use only at institutions which are participating in clinical trials with that particular device and will not be discussed.
The method of implantation of the free coils,[15],[16] detachable coils,[17] GGVOD[18] and Amplatzer duct occluder[19],[20] have been described elsewhere, as referenced and will not be discussed because of limitation of the space. The effectiveness of occlusion is good[13],[14] with all the above techniques; residual shunts 24 hours after the procedure were present in 18% patients with free Gianturco coils which decreased to 9% at follow-up. With detachable coils residual shunts were present in 7% to 28% immediately after the procedure which decreased further at follow-up to 3% to 12%. Residual shunts were present in 9% patients with GGVOD, all spontaneously closed during follow-up. Following implantation of the Amplatzer device residual shunt were seen in 5% to 34% which decreased to 0 to 3% at follow-up.[14] Of the 30 consecutive Amplatzer ductal occlusions during a twenty month period ending April 2005, performed by the author, 29 had complete closure at implantation and the 30th patient had complete closure at 3 month follow-up. The complications are minimal although coil/device embolization may occur, requiring transcatheter or occasionally surgical retrieval.[13],[14]
Gianturco coil occlusion of the PDA can be performed with small caliber catheters (#4F) and is the currently preferred method of occlusion for very small to small ductus. Small to moderate PDAs may need multiple coils[21] or larger wire diameter (0.52-in) coils.[22],[23],[24] For moderate to large-sized PDA, surgical, video-thoracoscopic and transcatheter device closure are the available options. Among the devices, GGVOD is approved for general clinical use and is useful in tubular PDAs. Amplatzer Duct Occluder has recently been approved by the FDA and is useful in closing moderate to large PDAs.[19],[20] Other devices are currently undergoing FDA-approved clinical trials and are available for investigational use at the participating hospitals and include Duct-occlud pfm and Folding plug buttoned device. Wireless PDA devices[25] may be used for very large PDA and are undergoing clinical trials outside USA. The choice of procedure depends upon the institutional experience and preference with these methods.
With wide spread use of color-Doppler echocardiography, a group of patients with color-Doppler evidence for small PDA, but without clinical features of PDA (no continuous murmur on auscultation), the so called "silent ductus" has emerged. There is no unanimity of opinion with regard to management of these patients, but the author does not recommend ductal occlusion for this group of patients.[26]
Subacute bacterial endocarditis prophylaxis is recommended for all PDAs. There may not be any need for this prophylaxis three months following surgical or transcatheter closure, provided there is no residual shunt. Considerations with regard to elevated pulmonary vascular resistance with PDA are similar to those discussed under VSD section.
References
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7. Hamdan MA, Cao Q, Hijazi ZM. Amplatzer septal occluder. In Rao PS, Kern MJ, eds. Catheter Based Devices for Treatment of Noncoronary Cardiovascular Disease in Adults and Children. Lippincott, Williams & Wilkins, Philadelphia, PA, 2003: 51-59.
8. Rao PS. Current status of cardiac interventions for pediatric congenital heart disease - Part II: Percutaneous closure of cardiac defects. Pediatric Cardiology Newsletter 2004; 6: 1-5.
9. Hijazi ZM, Hakim F, Abu Haweleh, A et al. Catheter closure of perimembraneous ventricular septal defects using new Amplatzer membranous VSD occluder: initial clinical experience. Cath Cardiovasc Intervent 2002; 56: 508-515.
10. Krichenko A, Benson L, Burrows P, Moes CF, McLaughlin P, Freedom RM. Angiographic classification of the isolated persistently patent ductus arteriosus and implications for percutaneous catheter occlusion. Am J Cardiol 1989; 63: 877-880.
11. Thapar MK, Rao PS, Rogers JH Jr., Moore HV and Strong WB. Changing murmur of patent ductus arteriosus. J Pediatr 1978; 92: 939-941.
12. Rao PS. History of transcatheter patent ductus arteriosus closure devices. In Rao PS, Kern MJ, eds, Catheter Based Devices for the Treatment of Noncoronary Cardiovascular Disease in Adults and Children. Lippincott, Williams & Wilkins, Philadelphia, PA, 2003, pp. 145-153.
13. Rao PS. Summary and comparison of patent ductus arteriosus closure devices. Current Intervent Cardiol Reports 2001; 3:268-274
14. Rao PS. Summary and comparison of patent ductus arteriosus closure methods. In Rao PS, Kern MJ, eds. Catheter Based Devices for the Treatment of Noncoronary Cardiovascular Disease in Adults and Children. Lippincott, Williams & Wilkins, Philadelphia, PA, 2003; 219-228.
15. Cambier PA, Kirby WC, Wortham DC et al. Percutaneous closure of small (< 2.5 mm) patent ductus arteriosus using coil embolization. Am J Cardiol 1992; 69: 815-816.
16. Rao PS, Sideris EB. Transcatheter closure of patent ductus arteriosus: State of the art. J Invas Cardiol 1996; 8: 278-288.
17. Tometzki AJ, Arnold R, Peart I et al. Transcatheter occlusion of patent ductus arteriosus with Cook detachable coils. Heart 1996; 76: 531-535.
18. Grifka RG, Vincent JA, Nihill MR et al. Transcatheter patent ductus arteriosus closure in an infant using Gianturco-Grifka device. Am J Cardiol 1996; 78: 721-723.
19. Masura J, Walsh KP, Thanopoulos B et al. Catheter closure of moderate-to-large-sized patent ductus arteriosus using new Amplatzer duct occluder; immediate and short-term results. J Am Coll Cardiol 1998; 31: 1878-1882.
20. Sandhu SK, King TD. Amplatzer duct occluder. In Rao PS, Kern MJ, eds. Catheter Based Devices for the Treatment of Noncoronary Cardiovascular Disease in Adults and Children. Lippincott, Williams & Wilkins, Philadelphia, PA, 2003; 214-218.
21. Hijazi ZM, Geggel RL. Results of antegrade transcatheter closure of patent ductus arteriosus using single or multiple Gianturco coils. Am J Cardiol 1994; 74:925-929.
22. Owada CY, Teitel DF, Moore P. Evaluation of Gianturco coils for closure of large (> 3.5 mm) patent ductus arteriosus. J Am Coll Cardiol 1997; 30:1859-1862.
23. Hayes MD, Hoyer NH, Glasgow PF. New forceps delivery technique for coil occlusion of patent ductus arteriosus. Am J Cardiol 1997; 80: 209-211.
24. Rao PS. Transcatheter closure of moderate-to-large patent ductus arteriosus. J Invasive Cardiol 2001; 13: 303-306.
25. Sideris EB, Rao PS, Zamora R. The Sideris' buttoned devices for transcatheter closure of patent ductus arteriosus. J Intervent Cardiol 2001; 14: 239-246.
26. Rao PS Transcatheter occlusion of patent ductus arteriosus: Which method to use and which ductus to close (Editorial). Am Heart J 1996; 132: 905-909.(Syamasundar Rao P)
Abstract
In this review, the clinical features and management of most commonly encountered acyanotic, left-to-right shunt lesions are discussed. Patients with small defects, especially in childhood, are usually asymptomatic while moderate to large defects in infancy may present with symptoms. Hyperdynamic precordium, widely split and fixed second heart sound, ejection systolic murmur at the left upper sternal border and a mid-diastolic flow rumble at the left lower sternal border are present in atrial septal defects, holosystolic murmur at the left lower border is characteristic for a ventricular septal defect whereas a continuous murmur at the left upper sternal border is distinctive for patent ductus arteriosus. Clinical diagnosis is not usually difficult and the diagnosis can be confirmed and quantitiated by non-invasive echocardiographic studies. Whereas surgical intervention was used in the past, transcatheter methods are increasingly used for closure of atrial septal defect and patent ductus arteriosus. Small ventricular septal defects may not need to be closed whereas medium and large defects may require surgical closure. Transcatheter closure of both muscular and membranous ventricular septal defects is feasible by transcatheter methodology, but these techniques are experimental at the time of this writing.
Keywords: Atrial septal defect; Ventricular septal defect; Patent ductus arteriosus; Transcatheter closure
As alluded to in the preceding paper, congenital heart defects (CHDs) may be classified into acyanotic and cyanotic, depending upon whether the patients clinically exhibit cyanosis. The acyanotic defects may further be subdivided into obstructive lesions and left-to-right shunt lesions. The obstructive lesions have been reviewed in the preceding paper. In this paper important findings in history, physical examination and laboratory studies that are suggestive of the diagnosis of the respective left-to-right shunt lesion and the available options in the management of these defects will be reviewed.
LEFT-TO-RIGHT SHUNT
When there is a defect in the partition between left and right heart structures, the oxygenated blood is shunted from left-to-right because of generally lower pressure and/or resistance in the right heart than in the left. The physical findings are either a manifestation of flow across the defects or due to effects of excessive flow across the cardiac chambers (volume overload) and valves or both. The magnitude of the shunt determines the clinical presentation and symptoms.
Atrial Septal Defect
There are three major types of atrial septal defects (ASDs) and these include ostium secundum, ostium primum and sinus venosus defects. The clinical features are essentially similar but I will mainly concentrate on ostium secundum ASDs. Atrial septal defects constitute 8% to 13% of all CHDs.[1] Pathologically, there is deficiency of the septal tissue in the region of fossa ovalis. The defects may be small to large. Most of the time, these are single defects, although, occasionally multiple defects and fenestrated defects can also be seen. Because of left-to-right shunting across the defects, the right atrium and right ventricle are dilated and somewhat hypertrophied. Similarly, main and branch pulmonary arteries are also enlarged. Pulmonary vascular obstructive changes are not usually seen until adulthood.
Symptoms : Isolated ASD patients are usually asymptomatic and are typically detected at the time of preschool physical examination. Sometimes these defects are detected when echocardiographic studies are performed for some unrelated reason. A few patients do present with heart failure in infancy, although this is uncommon.
Physical Examination: The right ventricular and right ventricular outflow tract impulses are increased and hyperdynamic. No thrills are usually felt. The second heart sound is widely split and fixed (splitting does not vary with respiration) and is the most characteristic sign of ASD. Ejection systolic clicks are rare with ASDs. An ejection systolic murmur is heard best at left upper sternal border; it is soft and is of grade II-III/VI intensity and rarely, if ever, louder. The murmur is secondary to increased flow across the pulmonary valve. A grade I-II/VI mid-diastolic flow rumble is heard (with the bell of the stethoscope) best at the left lower sternal border. This is due to large volume flow across the tricuspid valve. There is no audible murmur because of flow across the ASD.
Noninvasive Evaluation: Chest X-ray usually reveals mild to moderate cardiomegaly, prominent main pulmonary artery segment and increased pulmonary vascular markings Figure1. The electrocardiogram shows mild right ventricular hypertrophy; the so-called diastolic volume overload pattern with rSR' pattern in the right chest leads Figure2. Echocardiogram reveals enlarged right ventricle with paradoxical septal motion, particularly well-demonstrable on M-mode echocardiograms Figure3. By two-dimensional echocardiogram, the defect can be clearly visualized Figure3 and 4). The type of ASD, secundum Figure3 & Figure4 versus primum Figure5 can also be delineated by the echocardiographic study. Sinus venosus defects may escape detection and should be specifically looked for. Apical and precordial views may show "septal drop-outs" without an ASD because of thin-ness of the septum in the region of fossa ovalis. Therefore, subcostal views should he scrutinized for evidence of ASD. In addition, demonstration of flow across the defect with pulsed Doppler Figure6 and color Doppler echocardiography (not shown) is necessary to avid false positive studies.
Catheterization and Angiography: Clinical and echocardiographic features are sufficiently characteristic so that cardiac catheterization is not necessary for diagnosis. However, cardiac catheterization is an integral part of transcatheter occlusion of ASD.
When catheterization is performed, one will observe step-up in oxygen saturation at the right atrial level. The pulmonary venous, left atrial, left ventricular and aortic saturations are within normal range. In large defects, the pressures in both atria are equal while in small defects, an interatrial pressure difference is noted. The right ventricular and pulmonary arterial pressures are usually normal. Calculated pulmonary-to-systemic flow ratio (Qp:Qs) is used to quantitative the degree of shunting and a Qp:Qs in excess of 1.5:1 is considered an indication for closure of ASD.
Selective angiography in the right upper pulmonary vein at its junction with the left atrium in a four-chamber view will reveal location and the size of the ASD. When anomalous pulmonary venous connection is suspected, selective left or right pulmonary arterial angiography should be performed and the levophase of angiogram should be scrutinized for anomalous connections.
To avoid missing a diagnosis of partial anomalous pulmonary venous return, we usually perform a number of routine maneuvers and these include (i). Measurement of oxygen saturations from both right and left innominate veins at the time of superior vena caval sampling, (ii). Left innominate vein cineangiogram in posterior-anterior view with diluted contrast material, (iii). Probe for all the four pulmonary veins from the left atrium and (iv) . As mentioned before, obtain cineangiography from the right upper pulmonary vein at its junction with the left atrium in a left axial oblique (300 LAO and 300 cranial) view.
Management. Despite lack of symptoms at presentation, closure of the ASD is recommended so as to (i) prevent development of pulmonary vascular obstructive disease later in life, (ii) reduce probability for development of supraventricular arrhythmias and (iii) prevent symptoms during adolescence and adulthood. Elective closure around age 4 to 5 years is recommended. Closure during infancy is not undertaken unless the infant is symptomatic. Right ventricular volume overloading by echocardiogram and a Qp:Qs >1.5 (if the child had cardiac catheterization) are indications for closure.
The conventional treatment of choice is surgical correction. While the secundum ASDs can be successfully repaired by open-heart surgical techniques with a low (<1%) mortality, the morbidity with cardiac surgery is universal, and residual scar is present in all. Because of this reason several transcatheter methods have been developed.[2],[3] Clinical trials have been undertaken with a large number of devices as reviewed elsewhere[4],[5] and feasibility, safety and effectiveness of these devices in occluding the ASD have been demonstrated. Some of the devices have been discontinued and others modified and redesigned.[2],[3],[4],[5] At the present time, only one device, the Amplatzer Septal Occluder, is approved for general clinical use by the US Food and Drug Administration (FDA). A number of other devices are in FDA-approved (under Investigational Device Exemption) clinical trials with local IRB supervision. These devices, to the best of my knowledge, are CardioSeal/StarFlex, Helex device and transcatheter patch.
The Amplatzer Septal Occluder is rapidly becoming the device of choice because of ease with which the device can be implanted, retrieved and repositioned plus the comfort that the device is FDA approved. The procedure involves percutaneous right heart catheterization to confirm the clinical and echocardiographic diagnosis with particular attention to exclude partial anomalous pulmonary venous return. A left atrial cineangiogram in a left axial oblique view (300 LAO and 300 Cranial) with the catheter positioned in the right upper pulmonary vein at its junction with the left atrium is then performed. This is followed by transesophageal or intracardiac echocardiography to measure the size of the ASD, to visualize entry of all pulmonary veins into the left atrium and to examine the atrial septal rims. Static balloon sizing of the ASD using NuMed PTS or AGA Amplatzer sizing balloons should follow. During balloon occlusion, color Doppler evaluation of the atrial septum to rule out additional atrial defects should be carried out. An Amplatzer Septal Occluder that is 1 to 2 mm larger than the stretched diameter of the ASD is selected for implantation. The size of delivery sheath accommodating the selected device should then be positioned in the left upper pulmonary vein, taking appropriate precautions to avoid inadvertent air entry into the system. The selected device is screwed onto the delivery cable, the device is loosened by unscrewing by one turn and drawn into the loader sheath under saline. The device is deposited into the delivery sheath while flushing the loader sheath continuously with saline or a similar flushing solution. This is to prevent inadvertent air entry into the system. The device is advanced within the sheath under fluoroscopic guidance until it reaches the tip of the delivery sheath in the left upper pulmonary vein. It is important not to rotate the delivery cable to prevent inadvertent unscrewing of the device. The entire system is withdrawn until the tip of the sheath slips into the free left atrium and the device advanced, thus releasing the left atrial disk. Under echocardiographic guidance, the entire system is withdrawn such that the left atrial disk is flush against the left atrial side of the atrial septum occluding the ASD. Then, while the device cable is held steady, the delivery sheath is withdrawn releasing the waist of the device within the atrial septal defect, followed by further withdrawal of the sheath deploying the right atrial disk in the right atrium. The position of the device is verified by echocardiography and residual shunt looked for. If the device position is satisfactory, the device cable is moved back and forth (so called Minnesota Wiggle) and the device cable is rotated counterclockwise, releasing the device. If the device position is unsatisfactory, the device can be withdrawn into the sheath and redeployed. A repeat echocardiography to ensure good position of the device is undertaken. Right atrial cineangiography through the delivery sheath is performed by some cardiologists prior to withdrawal of the delivery sheath out of body. Arterial line to monitor the systemic pressures throughout the procedure, administration of heparin (100 units/kg) and monitoring the ACT to keep it above 200 seconds, and administration of Ancef or a similar antibiotic are routine parts of the procedure. Aspirin 5 mg/kg as a single daily dose for six months is usually recommended. Large defects, small septal rims, multiple defects and septal aneurysms pose additional problems and appropriate adjustments in the technique[6] should be undertaken to ensure success of the device implantation.
Both immediate and mid-term follow-up results of Amplatzer Septal Occluder appear excellent with immediate complete closure rates varying from 62% to 96% which improved to 83% to 99% at six to 12 month follow-up.[7] We undertook closure of 31 ostium secundum defects with this device; there was a small residual shunt in one patient at the conclusion of the procedure. This shunt disappeared at one month follow-up. No residual shunts observed during a mean follow-up of 12 months.
Ostium primum and sinus venosus defects are not amenable to transcatheter closure and surgical correction is the treatment of choice. Also, secundum defects not amenable to transcatheter closure are candidates for surgical closure. Surgery is usually performed under cardiopulmonary bypass and sternotomy. In the ostium primum defect, apart from closing the ASD, the mitral valve should be repaired in such a manner as to preserve its function. In sinus venosus defect, diversion of the anomalously connected right pulmonary vein(s) into the left atrium along with the closure of the ASD should be undertaken.
Ventricular Septal Defect
Ventricular septal defect (VSD) is the most common CHD and constitutes 20% to 25% of all CHDs.[1] The VSD may be small, medium or large and is classified based on its location in the interventricular septum. The defect is most commonly (80%) located in the membranous septum, in the subaortic region and is commonly referred to as perimembranous defect. The defect may also be located in the conal septum in the sub-pulmonary region and is called supracrystal defect and constitutes 5% to 7% of VSDs. This type of defect is more commonly encountered in the Far East including Japan and there it may constitute up to 29% of VSDs. The third type, in the posterior septum, is commonly referred to as atrioventricular canal defect and approximately 8% of the VSDs are of this type. Finally, the defect may be located in the muscular and apical portion of the ventricular septum and may make-up 5% to 20% of all VSDs. When multiple muscular defects are seen, it is often referred to as "Swiss-cheese" type of VSD.
Symptoms: The clinical symptomatology is largely dependent upon the size of the VSD. In small defects, the patients are usually asymptomatic and are detected because a cardiac murmur heard on routine examination. Patients with medium and large defects may present with symptoms of congestive heart failure (dyspnea, tachypnea, sweating and failure to gain weight) or with symptoms related to bronchial obstruction and/or respiratory infection.
Physical Findings: These, again, depend upon the size of the defect. In small defects the only abnormality is a loud holosystolic murmur Figure7 heard best at the left lower sternal border. When the VDS is small, the murmur is loud and is sometimes referred to as "maladie de Roger". Sometimes, the holosystolic murmur may be heard best at left mid and left upper sternal borders, depending upon the direction of the VSD jet. In very small defects, the murmur, though begins with first heart sound, may not last through the entire systole; the shorter the murmur, the smaller is the defect.
In medium and large defects, the right and left ventricular impulses are increased and somewhat hyperdynamic. A thrill may be felt at the left lower sternal border. The second heart sound is split unless there is pulmonary vascular obstructive disease, in which case a loud single second heart sound is heard. The pulmonary component of the second sound may be normal or increased, depending upon the degree of elevation pulmonary artery pressure. Clicks are unusual for VSD patients although they can be heard in patients whose VSDs are undergoing spontaneous closure by aneurismal formation of the membranous ventricular septum. A holosystolic murmur is best heard at the left lower sternal border and does not usually radiate although it may be widely heard over the precordium. The intensity of the murmur may vary between grade II-V/Vl. There is no significant variation of this murmur with respiration. This murmur is produced by flow across the VSD. The intensity of the murmur does not bear any consistent relationship with the size of the defect. A grade I-II/Vl mid-diastolic flow rumble may be heard at the apex in patients with medium to large-sized defects and large left-to-right shunts; this murmur is heard best with the bell of' the stethoscope. The mid diastolic murmur is due to increased flow across the mitral valve and usually indicates a Qp:Qs greater than 2:1.
Noninvasive Evaluation: Chest X-ray shows cardiomegaly and increased pulmonary vascular markings if the shunt is large. Left atrial enlargement may be noted. The electrocardiogram may be normal in very small defects or may show evidence for left ventricular hypertrophy in small to moderate defects while it may show biventricular or right ventricular hypertrophy in moderate to large defects. Electrocardiographic signs of left atrial enlargement may also be seen. Severe right ventricular hypertrophy may be seen if pulmonary vascular obstructive disease develops.
Echocardiogram shows increase in left atrial and left ventricular size, which is again dependent upon the size of the VSD. The location and size of the VSD can be imaged by 2-dimensional echocardiography Figure8 and Figure9. Left-to-right shunting across the VSD can be demonstrated by Doppler echocardiography (not shown). Peak Doppler flow velocity magnitude is inversely proportional to the size of defect. Indeed the right ventricular/pulmonary arterial pressures may be estimated by determining to peak Doppler flow velocity across the VSD.
RV/PA peak pressure = peak arm blood pressure - 4 VVSD2
where RV and PA are right ventricle and Pulmonary artery and VVSD is the peak Doppler velocity across the VSD.
The right ventricular peak pressure may also be estimated by tricuspid back flow (regurgitant) velocity:
RV peak pressure = 4 VTR2 + RAP
where VTR is peak tricuspid regurgitant velocity and RAP is estimated right atrial pressure (5 mmHg).
Both formulas may help to verify internal consistency of the Doppler methodology in estimating the size of the VSD. The higher the estimated RV pressure, larger is the size of the VSD.
Cardiac Catheterization & Cineangiography: Many of the issues that required definition by catheterization in the past can be resolved by good quality echo-Doppler studies and catheterization is not routinely required. When questions cannot be satisfactorily answered, cardiac catheterization may be useful.
Step-up in oxygen saturation is observed in the right ventricle. The saturations in the left-side of the heart are usually normal. The right ventricular and pulmonary arterial pressures are normal in small VSDs and are elevated in moderate to large defects; the magnitude of elevation is proportional to the size of the VSD. Calculated Qp:Qs gives an estimate of degree of left-to-right shunting. A Qp:Qs greater than 2:1 is generally considered an indication for intervention. Pulmonary vascular resistance may be calculated:
Mean PA presence - Mean LA pressure
PVR =
Pulmonary blood flow index
where PVR is pulmonary vascular resistance, PA and LA are pulmonary artery and left atrium respectively.
The calculated resistance is usually 1 to 2 units and a resistance in excess of 3.0 units is considered elevated. Marked elevation of the resistance (>8.0 units) contraindicates surgical repair. When the resistance is elevated, oxygen and other vasodilating agents should be administered to demonstrate the reversibility.
Selective left ventricular angiography in a left axial oblique view is usually required to demonstrate size and location of the VSD. Examples of a perimembranous and a muscular VSD are shown in [Figure - 10].
Natural History of VSDs: Knowledge of the natural history of these defects is interesting and such understanding is important in the management of these defects: (i) Spontaneous closure. Approximately 40% of VSDs spontaneously and completely close. Additional 25% to 30% of defects may become small enough not to require surgical intervention. While small defects tend to close more frequently than large defects (60% vs 20%), even defects large enough to produce congestive heart failure or require pulmonary artery banding in infancy go on to close spontaneously. The majority of the defects close by age 2, most close by age 5 to 7 years, but the process of spontaneous closure continues through adolescence and adulthood. Most commonly the defect closes by apposition of leaflets of the tricuspid valve against it or by aneurismal formation of the membranous ventricular septum. (ii) Pulmonary vascular obstructive disease may develop in 10% of VSDs. This is probably related to the exposure of the pulmonary vascular bed to high pressure and high flow. Prompt diagnosis and closure of the defect at least prior to 18 months of age is likely to reduce the incidence of development of pulmonary vascular disease, (iii) Development of infundibular stenosis, the so called Gasul's transformation of the VSD may occur in 8% of the defects. There may be specific markers such as right aortic arch and increased angle of the right ventricular outflow tract that may predispose a VSD to undergo Gasul's transformation. While development of infundibular stenosis eventually requires the patient to have surgery, it indeed protects the pulmonary vascular bed and prevents development of pulmonary vascular obstructive disease. (iv) Aortic insufficiency develops in approximately 5% of patients. This may either be related to prolapse of an aortic valve cusp into the VSD or lack of support to the aortic root. This complication appears to occur more commonly with supracrystal VSDs than with other types. Surgical correction is indicated if moderate to severe aortic insufficiency is present.
Management: The management strategies depend, to a large degree, on the size of the VSD. In small VSDs reassurance of the parents, subacute bacterial endocarditis prophylaxis and periodic clinical follow-up are all that are necessary. In moderate-sized defects, treatment of heart failure, if present, should be undertaken. Failure to thrive and markedly enlarged left ventricle are probably indications for surgical closure. In very large defects the heart failure should be treated aggressively. If the congestive heart failure is difficult to control with the usual anticongestive measures or if failure to thrive is present, surgical closure should be undertaken.
In large defects with near systemic pressures in the right ventricle and pulmonary artery, surgical closure should be performed prior to 18 to 24 months of age even if heart failure control and adequate weight gain are present. Total surgical correction is currently recommended. The previously used approach of initial pulmonary artery banding in small and young babies followed by surgical closure of the VSD later is no longer recommended. However, in muscular, Swiss-cheese variety of defects, initial pulmonary artery banding may be appropriate.
When the pulmonary vascular resistance is elevated, its response to oxygen and other vasodilator agents, pulmonary arterial wedge angiography and sometimes, even lung biopsy may be necessary to determine the suitability for surgical closure. Patients with calculated pulmonary vascular resistance less than 8 wood units with a Qp:Qs >1.5 are generally considered suitable candidates for surgery. If the resistance drops to levels below 8 units after administering oxygen or other vasodilator agents, the patient becomes a candidate for surgery.
Large VSDs with severe elevation of pulmonary resistance (irreversible pulmonary vascular obstructive disease) are not candidates for surgery. Symptomatic treatment and erythropheresis for symptoms of polycthemia should be undertaken. These patients may eventually become candidates for lung transplantation.
When surgery is indicated, open heart surgical technique is the treatment of choice. Some workers have attempted transcatheter occlusion of VSD in a manner similar ASD closure; a number of devices have been used for this purpose and include, Rashkind's double-umbrella, clamshell device, buttoned device, Amplatzer device, CardioSeal/StarFlex, and Nit-occlud.[8] Such method may be feasible in muscular defects and membranous defects with sufficient septum in the subaortic region so that the device can be implanted without interfering with aortic valve function. To circumvent this problem, the Amplatzer device was redesigned[9] such that the aortic end of the left ventricular disc is short (0.5 mm) while the opposite end is longer (5.5 mm). A platinum marker, to indicate the lower pole of the left ventricular disc, is built into the system and should be appropriately positioned during the device delivery and implantation. This modified device was used in children with small to medium-sized VSDs[9] and the results were good. Further experience with this device is necessary prior to its widespread use. At the present, transcatheter VSD occlusion is considered experimental.
Patent Ductus Arteriosus
Ductus arteriosus is one of the fetal circulatory pathways which diverts the desaturated blood from the main pulmonary artery into the descending aorta and placenta for oxygenation. After the infant is born, the ductus arteriosus constricts and closes spontaneously, presumably secondary to increased PO2. But in some children, such spontaneous closure does not occur. This is more frequent in prematurely born infants. Patent ductus arteriosus (PDA) may be an isolated lesion and may be present in association with other defects. Isolated PDA constitutes 6 to 11% of all CHDs.[1] In this section, isolated PDA beyond neonatal (and premature) period will be discussed. PDA is a muscular structure connecting the main pulmonary artery (at its junction with the left pulmonary artery) with the descending aorta at the level of left subclavian artery. The configuration of PDA varies considerably but most often it has a conical or funnel shape. The aortic end is wide and gradually narrows (ampulla) towards the pulmonary end. The narrowest segment is at the pulmonary end. Other types which are short and tubular and those with multiple constrictions and bizarre configuration can also be seen.[10] Because of usually higher pressure and resistance in the systemic circuit than in the pulmonary circuit, left-to-right shunt takes place across the PDA. The magnitude of left-to-right shunting depends upon the diameter of the ductus and ratio of pulmonary to systemic vascular resistance.
Symptoms: Clinical presentation depends upon the size of the ductus. If the PDA is small, there are no symptoms and it is usually detected because of a murmur detected on a routine examination. Moderate to large ductus with large shunt may either present with symptoms of easy fatigability, symptoms associated congestive heart failure or respiratory symptoms suggestive of lung collapse (very large ductus in small babies).
Physical Findings: Left ventricular impulse may be hyperdynamic with large shunts. A thrill may be felt at the left upper sternal border and in the suprasternal notch. The first heart sound is usually normal and the second heart sound may be buried within the murmur. In the majority of cases, a continuous murmur [Figure - 11] is heard best at the left upper sternal border. The murmur begins in systole and continues through the second heart sound into the diastole. The systolic component of the murmur crescendos up to the second heart sound while the diastolic part descrescendos to a varying distance (time) into the diastole. The continuous murmur must be distinguished from the to-and-fro murmur; the latter is a combination of an ejection systolic murmur and an early diastolic descrescendo murmur (for example aortic stenosis and insufficiency) and there is a definite gap between the end of the ejection murmur and the second heart sound, while no such gap is auscultated with continuous murmurs [Figure - 11]. The continuous murmur of PDA may be of grade I-V/VI in intensity. There is some beat-to-beat variation in the intensity of the murmur and for this reason it is described as machinery murmur. Multiple ejection clicks are usually heard within the murmur and this is rather characteristic of the PDA. The majority of the time, the murmur does not change with the position of the body, although the diastolic component of the murmur is heard better in a supine than in an upright position. However, in patients with very small PDA, the continuous murmur of the PDA either completely disappears or becomes only systolic in timing when the patient sits up and returns to continuous quality when the patient assumes supine position. The postulated cause of this is "kinking" of the ductus in the upright position.[11] When the ductus is moderate to large in size, a mid-diastolic murmur may be heard at the apex because of increased flow across the mitral valve, such a mid-diastolic murmur suggests a Qp:Qs greater than 2:1. Arterial pulses are bounding in all but patients with very small ductus.
Noninvasive Evaluation: Chest X-ray may show a normal-sized heart with normal pulmonary vascular markings with small ductus while cardiomegaly, increased pulmonary blood flow and left atrial enlargement may be seen with moderate to large ductus. Collapse with secondary inflammatory process may be observed in the lung fields of small children with large ductus. The electrocardiogram may be normal or may show left atrial and left ventricular enlargement, depending upon the size of the ductus. Biventricular hypertrophy may be seen large ductus and right ventricular hypertrophy in patients with pulmonary vascular obstructive disease.
Echocardiogram may reveal varying degrees of left atrial and left ventricular enlargement, again depending upon the size of the ductus. The left ventricular contraction indices are normal to elevated unless severe myocardial dysfunction sets in. Doppler echocardiography shows characteristic diastolic flow pattern in the pulmonary artery [Figure - 12], indicative of PDA. Characteristic color flow mapping distribution (not shown) is also present.
Cardiac Catheterization and Selective Cine Angiography: These invasive studies are not necessary in the usual cases of PDA, although these procedures are integral parts of transcatheter closure.
Oxygen saturation data show a step up in oxygen saturation at the pulmonary artery level. The left heart saturations are usually normal. Calculated Qp:Qs, though usually indicates degree of shunting, it may not be accurate because of the difficulty in obtaining reliable mixed pulmonary arterial saturations. The right ventricular and pulmonary arterial pressures are normal in patients with small PDA but may be elevated if the PDA is moderate or large. Wide pulse pressure is observed in the aorta.
Selective aortic arch angiogram demonstrates the size, shape and location of the ductus and are demonstrated in [Figure - 13].
Management: It is generally believed that the presence of an isolated ductus is an indication for closure, mainly to prevent bacterial endocarditis. This can be performed at anytime, especially if associated with heart failure or pulmonary compromise. If the patient is asymptomatic, waiting until 6 to 12 months of age is generally recommended. Since the description of successful surgical ligation of patent ductus arteriosus by Gross and Hubbard in 1939, surgery has been extensively used in the treatment of PDA and has become the treatment of choice. The procedure involves thoracotomy under general anesthesia and ductal ligation or ligation and division, as per the surgeon's preference. While the risk of surgical closure is low, morbidity associated with it, namely anesthesia, endotracheal intubation and thoracotomy is universal. Because of this reason, less invasive, transcatheter closure techniques have been developed.[12] These transcatheter methods are increasingly being used in closing PDAs. A number of PDA occluding devices have been designed and investigated in human clinical trials as reviewed elsewhere;[13],[14] and include Ivalon foam plug, polyurethane foam covered single umbrella with miniature hooks, Rashkind PDA occluder system, Botallo-occluder, adjustable buttoned device, clamshell ASD device, Gianturco Coil, duct-occlude pfm, Cook detachable coil, flipper detachable coil, Gianturco-Grifka Vascular Occlusion Device (GGVOD), infant buttoned device, polyvinyl alcohol foam plug, Amplatzer duct-occluder, folding plug buttoned device, and wireless PDA devices. Gianturco coils (both free and detachable), GGVOD and Amplatzer duct occluder are currently available for routine clinical use. The remaining devices, at the time of this writing, have not received approval from the appropriate regulatory authority, but are available for use only at institutions which are participating in clinical trials with that particular device and will not be discussed.
The method of implantation of the free coils,[15],[16] detachable coils,[17] GGVOD[18] and Amplatzer duct occluder[19],[20] have been described elsewhere, as referenced and will not be discussed because of limitation of the space. The effectiveness of occlusion is good[13],[14] with all the above techniques; residual shunts 24 hours after the procedure were present in 18% patients with free Gianturco coils which decreased to 9% at follow-up. With detachable coils residual shunts were present in 7% to 28% immediately after the procedure which decreased further at follow-up to 3% to 12%. Residual shunts were present in 9% patients with GGVOD, all spontaneously closed during follow-up. Following implantation of the Amplatzer device residual shunt were seen in 5% to 34% which decreased to 0 to 3% at follow-up.[14] Of the 30 consecutive Amplatzer ductal occlusions during a twenty month period ending April 2005, performed by the author, 29 had complete closure at implantation and the 30th patient had complete closure at 3 month follow-up. The complications are minimal although coil/device embolization may occur, requiring transcatheter or occasionally surgical retrieval.[13],[14]
Gianturco coil occlusion of the PDA can be performed with small caliber catheters (#4F) and is the currently preferred method of occlusion for very small to small ductus. Small to moderate PDAs may need multiple coils[21] or larger wire diameter (0.52-in) coils.[22],[23],[24] For moderate to large-sized PDA, surgical, video-thoracoscopic and transcatheter device closure are the available options. Among the devices, GGVOD is approved for general clinical use and is useful in tubular PDAs. Amplatzer Duct Occluder has recently been approved by the FDA and is useful in closing moderate to large PDAs.[19],[20] Other devices are currently undergoing FDA-approved clinical trials and are available for investigational use at the participating hospitals and include Duct-occlud pfm and Folding plug buttoned device. Wireless PDA devices[25] may be used for very large PDA and are undergoing clinical trials outside USA. The choice of procedure depends upon the institutional experience and preference with these methods.
With wide spread use of color-Doppler echocardiography, a group of patients with color-Doppler evidence for small PDA, but without clinical features of PDA (no continuous murmur on auscultation), the so called "silent ductus" has emerged. There is no unanimity of opinion with regard to management of these patients, but the author does not recommend ductal occlusion for this group of patients.[26]
Subacute bacterial endocarditis prophylaxis is recommended for all PDAs. There may not be any need for this prophylaxis three months following surgical or transcatheter closure, provided there is no residual shunt. Considerations with regard to elevated pulmonary vascular resistance with PDA are similar to those discussed under VSD section.
References
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