Continuous retrograde blood cardioplegia ensures prolonged aortic cross-clamping time without increasing the operative risk
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《交互式心脏血管和胸部手术》
Department of Cardiovascular and Thoracic Surgery, University Hospital La Cavale Blanche, Brest, France
Abstract
The aim of this study was to assess whether the continuous retrograde blood cardioplegia ensures prolonged aortic cross-clamping time without increasing the operative risk. From 1996 to 2003, 204 consecutive patients who had cardiac procedure requiring aortic cross-clamping time 150 min, were prospectively included in this study: low risk group (EuroSCORE 2) 50 patients, medium risk group (EuroSCORE 3–5) 68 patients, high risk group (EuroSCORE 6) 86 patients. The myocardial protection associated induction of cardiac arrest by antegrade injection of hyperkalemic warm blood, continuous retrograde intermediate lukewarm (20 °C) blood cardioplegia, retrograde warm blood reperfusion and systemic normothermia. The mean aortic clamping time was 187±45 min (range 150–436 min). The mean cardiopulmonary bypass time was 245±73 min (range 168–653 min). The operative mortality was 8.3% (17 patients). The mean predicted mortality of the population studied (EuroSCORE logistic method) was 8.4%±12 (range 0.87%–76.15%) with a 95% confidence interval of 6.7% to 10%. The observed mortality was not different from the predicted mortality. Continuous retrograde intermediate lukewarm blood cardioplegia associated with systemic normothermia allows prolonged aortic clamping time for complex intervention without increase of operative mortality and morbidity.
Key Words: Cardioplegia; Cardiac surgery; Myocardial protection
1. Introduction
A long aortic cross-clamp time is a significant risk factor for predictors of postoperative morbidity and mortality [1]. Efforts to avoid intraoperative myocardial infarction and post-operative low cardiac output due to inadequate myocardial protection have led to the development of numerous methods of myocardial protection.
The safety of any cardioprotective strategy has been reported in the literature. The efficacy of myocardial protection can be gauged to a large degree by the safe period of aortic occlusion. Few reports examined the efficacy of myocardial protection for cardiac procedure which required prolonged aortic cross-clamping time.
The aim of this study was to assess whether the continuous retrograde blood cardioplegia ensures prolonged aortic cross-clamping time without increasing the operative risk.
2. Patients and methods
From 1996 to 2003, among the 1215 patients operated on by the younger surgeon of our unit, using cardiopulmonary bypass and continuous retrograde blood cardioplegia, 204 consecutive patients who had cardiac procedure requiring aortic cross-clamping time 150 min, were included in this study. Then, the collection of the data was obtained prospectively. The mean age was 63.2±9.1 years (range 40–83 years). The European system for cardiac operative risk evaluation (EuroSCORE) is a scoring system for the prediction of early mortality in cardiac surgical patients in Europe [2]. Patient's data and risk factors for adverse outcomes, according to the EuroSCORE are reported in Table 1. The population studied was divided into 3 groups: the low risk group (EuroSCORE 2) 50 patients, the medium risk group (EuroSCORE 3–5) 68 patients, the high risk group (EuroSCORE 6) 86 patients.
Surgical procedures are listed in Table 2. Two-hundred and ninety-nine coronary artery bypass grafts were performed on 112 patients with 173 left internal thoracic arteries, 57 right internal thoracic arteries, 21 right gastro-epiploic arteries, 2 radial arteries, and 46 saphenous veins. A coronary artery reconstruction [3] was performed in 169 cases (55%). The length of the coronary artery reconstruction exceeded 4 cm in 111 cases; an endarterectomy was adjunct in 53 cases (29%).
Normothermic cardiopulmonary bypass was employed except for aortic arch replacement. The heart was arrested by antegrade injection of 100 ml of warm undiluted arterial blood (37 °C) added to 2 g of potassium chloride and 100 mg of Xylocaine?. Then, the cardioplegia was injected through the coronary sinus in almost uninterrupted fashion throughout the period of aortic cross-clamping. Perfusion pressure in the coronary sinus was maintained in the range of 40 mmHg with a perfusion flow in the range of 150 ml/min. Continuous drainage of cardioplegic effluent was ensured by aortic vent. During coronary surgery, a blower was used to ensure a good vision of the arteriotomy. If necessary, the cardioplegic flow was halted in the following situations: performing coronary endarterectomy, searching coronary artery in intramyocardial position, suturing the aortic valve to the annular segment related to the left coronary sinus, and anastomosing of the inferior border of the left coronary ostium to the aortic graft in the case of aortic root replacement. The cardioplegia was formed of intermediate lukewarm undiluted arterial blood (20 °C) mixed with a cardioplegic solution of 10 ml of a citrate-phosphate-dextrose solution, 3 g of potassium chloride, 1 g of magnesium sulphate and 5 ml of Xylocaine? (2%). The cardioplegic solution is injected by means of an infusion pump at a flow rate of 600 ml/h during the first min and reduced to 40 ml/h thereafter. A warm reperfusate was delivered through the coronary sinus before arortic declamping. The reperfusion solution was 750 ml of warm undiluted arterial blood (37 °C) added to 1 g of potassium chloride, 10 ml of mannitol (10%), 10 ml of sodium bicarbonate (4.2%), 20 ml of glutamic acid, 1 g of magnesium sulphate and 50 mg of Xylocaine?. The aorta was unclamped while the cardiopulmonary bypass flow was stopped. Then, the cardiopulmonary bypass flow was progressively brought up to the anterior output. The weaning from the cardiopulmonary bypass was achieved after a period of assistance until obtaining efficient ventricular contractility. The mean aortic clamping time was 187±45 min (range 150–436 min).
Operative criteria were: the spontaneous defibrillation or not on, the need for inotropic agents (dobutamine 5 μg/kg/min or adrenaline) or an intraaortic balloon pump, or both, to wean from the cardiopulmonary bypass, the cardiopulmonary bypass time. Operative mortality and morbidity were defined as any death or any complication occurring within 30 days postoperatively if the patient had been discharged from the hospital, or any death occurring during the period of postoperative hospitalization. The duration of intubation was the time from the admission to the intensive care unit until complete weaning from mechanical ventilation. Low cardiac output syndrome was defined as the need for inotropic agents (dobutamine 5 μg/kg/min or adrenaline) or an intraaortic balloon pump, or both, to keep systolic blood pressure above 90 mmHg. Perioperative myocardial infarction was defined as electrocardiographic criteria in association with elevation of the troponin I serum level. Postoperative renal insufficiency was defined as increase of serum creatinine level up to 120 μmol/l. Pulmonary complications were defined as adult respiratory distress syndrome or pneumonia. Sternal wound infections were defined as infections that required operative intervention. Transient ischemic attack was defined as a neurological deficit lasting less than 24 h and stroke as neurological deficit lasting up to the time of hospital discharge. Postoperative psychological disturbances were defined as confusion, disorientation, hallucination.
The expected mortality was calculated by the EuroSCORE logistic method retrospectively for patients operated until 2000 and prospectively thereafter (http://www.SFAR.org/scores/euroscore.html). The mean expected operative mortality was calculated for each risk group. If the observed operative mortality was included in the 95% confidence interval of the mean predicted operative mortality, we concluded the absence of statistical significance.
3. Results
Nine hearts (4%) required electrical defibrillation. Weaning from the cardiopulmonary bypass was difficult in 12 patients (6%); all of them required inotropic agents, four an intra-aortic balloon pump and two a new cardiopulmonary bypass. The mean cardiopulmonary bypass time was 245±73 min (range 168–653 min).
Two patients were dead per operatively (aortic dissection). The mean predicted mortality of the population studied was 8.4%±12 (range 0.87–76.15%) with a 95% confidence interval of 6.7 to 10%. The observed mortality was 8.3% (17 patients). The observed mortality was not different from the predicted mortality. Causes of death are indicated in Table 3. Comparisons between observed and expected mortality for each risk group are presented in Table 4.
Postoperative complications are listed in Table 5. One-hundred and seventy-nine patients (88%) were weaned from the ventilator and extubated within 24 h postoperatively. There was a 60% (122 patients) complications free rate.
4. Discussion
Advances in myocardial protection have been accompanied by a greater understanding of cardiac physiology and metabolism during ischemia and reperfusion. However, nobody can answer this question: "which is the best method of myocardial protection?". Why is it so difficult to highlight this best myocardial protection in the surgical practice? Probably because randomized prospective clinical trials comparing the use of different procedures of myocardial protection on prolonged aortic cross-clamping time do not exist. The efficacy of myocardial protection can be gauged to a large degree by the safe period of aortic occlusion that it affords the surgeon. Prolonged aortic cross-clamping time represents a rigorous test of the myocardial preservation. We have suggested that the term ‘long aortic cross-clamping time’ could be referred to time equal to or more than 150 min, depending on the few studies which reported this subject [4,5].
The effectiveness of the EuroSCORE has been demonstrated and allowed to compare the observed mortality rate to the expected one. Our study is not a randomized one. It describes the operative results of a historical cohort. Using intermediate lukewarm blood (20 °C) retrograde cardioplegia is the result of gradual evolution of the myocardial protection in our unit in the 1990s. We thought that it was not ethical to compare this technique to a crystalloid one or antegrade one because we suspected in a previous report that the cold crystalloid antegrade cardioplegia increases by four times the risk of perioperative myocardial infarction [3].
The induction of cardiac arrest by antegrade injection of hyperkalemic warm blood allows cardiac arrest in diastole and the restoration of high energy phosphate level [6]. The efficiency of myocardial protection obtained by retrograde cardioplegia had been demonstrated [7]. However, the disadvantage of retrograde cardioplegia remains a non-constant cardioplegic distribution to the interventricular septum and to the right ventricle [8]. It would be due to anatomical variations. The posterior interventricular vein which drains the left ventricular posterior wall as well as the posterior fourth of the interventricular septum [9], flows into the right atrium by the Thebesius veins in 13% of cases [9]. In these cases, the posterior fourth of the interventricular septum could not be well preserved by retrograde cardioplega. The small coronary vein which drains the right ventricle joins the coronary sinus in 40% of cases while in 60% of cases this vein drains into the right atrium or the right ventricle by the Thebesius veins [9]. In this condition, retrograde cardioplegia could not protect well the right ventricle. However, there was no postoperative septal or right ventricular infarction in our study. The protection of the posterior fourth of the interventricular septum and of the right ventricle was probably achieved by the venous network between the principal coronary veins [9] and by the cooling of intermediate lukewarm blood (20 °C) cardioplegia through the Thebesius vein. The superiority of blood cardioplegia on crystalloid cardioplegia had been demonstrated [10]. However, the temperature of blood cardioplegia remains a matter of controversy. Blood temperature between 20 and 25 °C seems to be the most appropriate [11]. Myocardial oxygen consumption is least during hyperkalemic arrest associated with moderate (22 °C) hypothermia [12]. High hypothermia (10 °C) increases blood viscosity and shifts the oxygen–hemoglobin dissociation curve leftward [13] while normothermia could not provide complete right ventricular preservation in the case of retrograde injection [14]. Continuous perfusion of blood cardioplegia can thus avoid myocardial ischemia eliminating the correlation between aortic cross-clamp time and ischemic time. The retrograde injection of warm blood enriched solution before removing the aortic clamp prevents reperfusion injury [15]. Finally, improving myocardial protection allows systemic normothermia, thus avoiding metabolic and hemodynamic effects of the hypothermia.
The observed operative mortality is similar to the series studied for long aortic cross-clamping time [4,5]. It remains close to the overall operative mortality in cardiac surgery. In-hospital mortality (Tables 3 and 5) was mainly related to non-cardiac causes (76%). They were probably more reliable for the patient-related factors rather than for the aortic cross-clamping time; 88% of the deaths occurred in patients of the high-risk group (Table 4). Comparison of the observed in-hospital mortality to the expected one, according to the EuroSCORE, has demonstrated that prolonged aortic clamping time with our myocardial protection does not aggravate operative mortality. This fact was not only established in the case of high risk patients but also in the case of low and medium risk patients. These results encourage us to perform extensive coronary artery reconstruction surgery [3], requiring longer cross aortic clamping time for low or medium risk patients.
The incidence of cardiac and non-cardiac-related complications (Table 5) did not seem to be different from the in-hospital morbidity associated with the usual cardiac surgery. In our study, the duration of post-operative mechanical ventilation is not expressed as a mean ± standard deviation for two reasons. Firstly, 7 patients had prolonged mechanical ventilation longer than 6 days which could increase the mean value. Secondly, fast-track cardiac anesthesia techniques were introduced gradually during the period of the study thus allowing early tracheal extubation. The patients operated during the last three years had the shortest duration of mechanical ventilation.
Continuous retrograde intermediate lukewarm undiluted blood cardioplegia associated with systemic normothermia allows prolonged aortic clamping time for complex intervention without increase of operative mortality and morbidity.
Acknowledgements
We would like to express our thanks to Fran?ois Roques, M.D., for help in comparing the observed operative mortality to the expected one calculated with the the EuroSCORE logistic method.
References
Kirklin JW. The science of cardiac surgery. Eur J Cardiothorac Surg 1990; 4:53–71.
Nashef SAM, Roques F, Michel P, Gauducheau E, Lemeshow S, Salamon R. the EuroSCORE study group. European system for cardiac operative risk evaluation (EuroSCORE). Eur J Cardiothorac Surg 1999; 16:9–13.
Barra JA, Bezon E, Mondine P, Resk A, Gilard M, Mansourati J, Boshat J. Surgical angioplasty with exclusion of atheromatous plaques in case of diffuse disease of the left anterior descending artery: 2 years' follow-up. Eur J Cardio-thorac Surg 2000; 17:509–514.
Bar-El Y, Adler Z, Kophit A, Kertzman V, Sawaed S, Ross A, Cohen O, Milo S. Myocardial protection in operations requiring more than 2 h of aortic cross-clamping. Eur J Cardiothorac Surg 1999; 15:271–275.
Chitwood WR Jr, Wixon CL, Norton TO, Lust RM. Complex valve operations: antegrade versus retrograde cardioplegia? Ann Thorac Surg 1995; 60:815–818.
Rosenkranz ER, Vinten-Johansen J, Buckberg GD, Okamoto F, Edwards H, Bugyi H. Benefits of normothermic induction of blood cardioplegia in energy-depleted hearts, with maintenance of arrest by multidose cold blood cardioplegia infusions. J Thorac Cardiovasc Surg 1982; 84:667–677.
Menasche P, Subayi JB, Veyssie L, Le Dref O, Chevret S, Piwnica A. Efficacy of coronary sinus cardioplegia in patients with complete coronary artery occlusions. Ann Thorac Surg 1991; 51:418–423.
Crooke GA, Harris LH, Grossi EA, Baumann FG, Galloway AC, Colvin SB. Biventricular distrubution of cold blood cardioplegic solution administered by different retrograde techniques. J Thorac Cardiovasc Surg 1991; 102:631–638.
Lüdinghausen MV. Nomenclature and distribution pattern of cardiac veins in man. In: Mohl W, Faxon D, Wolner E. eds. Clinics of CSI: 2nd International Symposium on Myocardial Protection in the Coronary Sinus 1986;New York: Springer-Verlag 13–32. In:.
Loop FD, Higgins TL, Panda R, Pearce G, Estafanous FG. Myocardial protection during cardiac operations. Decreased morbidity and lower cost with blood cardioplegia and coronary sinus perfusion. J Thorac Cardiovasc Surg 1992; 104:608–618.
Hayashida N, Weisel RD, Shirai T, Ikonomidis JS, Ivanov J, Carson SM, Mohabeer MK, Tumiati LC, Mickle DA. Tepid antegrade and retrograde cardioplegia. Ann Thorac Surg 1995; 59:723–729.
Buckberg GD, Brazier JR, Nelson RL, Goldstein SM, McConnell DH, Cooper N. Studies of the effects of hypothermia on regional myocardial blood flow and metabolism during cardiopulmonary bypass. I. The adequately perfused beating, fibrillating, and arrested heart. J Thorac Cardiovasc Surg 1977; 73:87–94.
Magovern Jr GJ, Flaherty JT, Gott VL, Bulkley BH, Gardner TJ. Failure of blood cardioplegia to protect myocardium at lower temperatures. Circulation 1982; 66:60–67.
Calderone CA, Krukenkamp IB, Misare BO. Perfusion deficits with retrograde warm blood cardioplegia. Ann Thorac Surg 1994; 57:403–406.
Julia PL, Buckberg GD, Acar C, Partington MT, Sherman MP. Studies of controlled reperfusion after ischemia. XXI. Reperfusate composition: superiority of blood cardioplegia over crystalloid cardioplegia in limiting reperfusion damage. Importance of endogenous oxygen free radical scavengers in red blood cells. J Thorac Cardiovasc Surg 1991; 101:303–313.(Eric Bezon, Jean No?l Cho)
Abstract
The aim of this study was to assess whether the continuous retrograde blood cardioplegia ensures prolonged aortic cross-clamping time without increasing the operative risk. From 1996 to 2003, 204 consecutive patients who had cardiac procedure requiring aortic cross-clamping time 150 min, were prospectively included in this study: low risk group (EuroSCORE 2) 50 patients, medium risk group (EuroSCORE 3–5) 68 patients, high risk group (EuroSCORE 6) 86 patients. The myocardial protection associated induction of cardiac arrest by antegrade injection of hyperkalemic warm blood, continuous retrograde intermediate lukewarm (20 °C) blood cardioplegia, retrograde warm blood reperfusion and systemic normothermia. The mean aortic clamping time was 187±45 min (range 150–436 min). The mean cardiopulmonary bypass time was 245±73 min (range 168–653 min). The operative mortality was 8.3% (17 patients). The mean predicted mortality of the population studied (EuroSCORE logistic method) was 8.4%±12 (range 0.87%–76.15%) with a 95% confidence interval of 6.7% to 10%. The observed mortality was not different from the predicted mortality. Continuous retrograde intermediate lukewarm blood cardioplegia associated with systemic normothermia allows prolonged aortic clamping time for complex intervention without increase of operative mortality and morbidity.
Key Words: Cardioplegia; Cardiac surgery; Myocardial protection
1. Introduction
A long aortic cross-clamp time is a significant risk factor for predictors of postoperative morbidity and mortality [1]. Efforts to avoid intraoperative myocardial infarction and post-operative low cardiac output due to inadequate myocardial protection have led to the development of numerous methods of myocardial protection.
The safety of any cardioprotective strategy has been reported in the literature. The efficacy of myocardial protection can be gauged to a large degree by the safe period of aortic occlusion. Few reports examined the efficacy of myocardial protection for cardiac procedure which required prolonged aortic cross-clamping time.
The aim of this study was to assess whether the continuous retrograde blood cardioplegia ensures prolonged aortic cross-clamping time without increasing the operative risk.
2. Patients and methods
From 1996 to 2003, among the 1215 patients operated on by the younger surgeon of our unit, using cardiopulmonary bypass and continuous retrograde blood cardioplegia, 204 consecutive patients who had cardiac procedure requiring aortic cross-clamping time 150 min, were included in this study. Then, the collection of the data was obtained prospectively. The mean age was 63.2±9.1 years (range 40–83 years). The European system for cardiac operative risk evaluation (EuroSCORE) is a scoring system for the prediction of early mortality in cardiac surgical patients in Europe [2]. Patient's data and risk factors for adverse outcomes, according to the EuroSCORE are reported in Table 1. The population studied was divided into 3 groups: the low risk group (EuroSCORE 2) 50 patients, the medium risk group (EuroSCORE 3–5) 68 patients, the high risk group (EuroSCORE 6) 86 patients.
Surgical procedures are listed in Table 2. Two-hundred and ninety-nine coronary artery bypass grafts were performed on 112 patients with 173 left internal thoracic arteries, 57 right internal thoracic arteries, 21 right gastro-epiploic arteries, 2 radial arteries, and 46 saphenous veins. A coronary artery reconstruction [3] was performed in 169 cases (55%). The length of the coronary artery reconstruction exceeded 4 cm in 111 cases; an endarterectomy was adjunct in 53 cases (29%).
Normothermic cardiopulmonary bypass was employed except for aortic arch replacement. The heart was arrested by antegrade injection of 100 ml of warm undiluted arterial blood (37 °C) added to 2 g of potassium chloride and 100 mg of Xylocaine?. Then, the cardioplegia was injected through the coronary sinus in almost uninterrupted fashion throughout the period of aortic cross-clamping. Perfusion pressure in the coronary sinus was maintained in the range of 40 mmHg with a perfusion flow in the range of 150 ml/min. Continuous drainage of cardioplegic effluent was ensured by aortic vent. During coronary surgery, a blower was used to ensure a good vision of the arteriotomy. If necessary, the cardioplegic flow was halted in the following situations: performing coronary endarterectomy, searching coronary artery in intramyocardial position, suturing the aortic valve to the annular segment related to the left coronary sinus, and anastomosing of the inferior border of the left coronary ostium to the aortic graft in the case of aortic root replacement. The cardioplegia was formed of intermediate lukewarm undiluted arterial blood (20 °C) mixed with a cardioplegic solution of 10 ml of a citrate-phosphate-dextrose solution, 3 g of potassium chloride, 1 g of magnesium sulphate and 5 ml of Xylocaine? (2%). The cardioplegic solution is injected by means of an infusion pump at a flow rate of 600 ml/h during the first min and reduced to 40 ml/h thereafter. A warm reperfusate was delivered through the coronary sinus before arortic declamping. The reperfusion solution was 750 ml of warm undiluted arterial blood (37 °C) added to 1 g of potassium chloride, 10 ml of mannitol (10%), 10 ml of sodium bicarbonate (4.2%), 20 ml of glutamic acid, 1 g of magnesium sulphate and 50 mg of Xylocaine?. The aorta was unclamped while the cardiopulmonary bypass flow was stopped. Then, the cardiopulmonary bypass flow was progressively brought up to the anterior output. The weaning from the cardiopulmonary bypass was achieved after a period of assistance until obtaining efficient ventricular contractility. The mean aortic clamping time was 187±45 min (range 150–436 min).
Operative criteria were: the spontaneous defibrillation or not on, the need for inotropic agents (dobutamine 5 μg/kg/min or adrenaline) or an intraaortic balloon pump, or both, to wean from the cardiopulmonary bypass, the cardiopulmonary bypass time. Operative mortality and morbidity were defined as any death or any complication occurring within 30 days postoperatively if the patient had been discharged from the hospital, or any death occurring during the period of postoperative hospitalization. The duration of intubation was the time from the admission to the intensive care unit until complete weaning from mechanical ventilation. Low cardiac output syndrome was defined as the need for inotropic agents (dobutamine 5 μg/kg/min or adrenaline) or an intraaortic balloon pump, or both, to keep systolic blood pressure above 90 mmHg. Perioperative myocardial infarction was defined as electrocardiographic criteria in association with elevation of the troponin I serum level. Postoperative renal insufficiency was defined as increase of serum creatinine level up to 120 μmol/l. Pulmonary complications were defined as adult respiratory distress syndrome or pneumonia. Sternal wound infections were defined as infections that required operative intervention. Transient ischemic attack was defined as a neurological deficit lasting less than 24 h and stroke as neurological deficit lasting up to the time of hospital discharge. Postoperative psychological disturbances were defined as confusion, disorientation, hallucination.
The expected mortality was calculated by the EuroSCORE logistic method retrospectively for patients operated until 2000 and prospectively thereafter (http://www.SFAR.org/scores/euroscore.html). The mean expected operative mortality was calculated for each risk group. If the observed operative mortality was included in the 95% confidence interval of the mean predicted operative mortality, we concluded the absence of statistical significance.
3. Results
Nine hearts (4%) required electrical defibrillation. Weaning from the cardiopulmonary bypass was difficult in 12 patients (6%); all of them required inotropic agents, four an intra-aortic balloon pump and two a new cardiopulmonary bypass. The mean cardiopulmonary bypass time was 245±73 min (range 168–653 min).
Two patients were dead per operatively (aortic dissection). The mean predicted mortality of the population studied was 8.4%±12 (range 0.87–76.15%) with a 95% confidence interval of 6.7 to 10%. The observed mortality was 8.3% (17 patients). The observed mortality was not different from the predicted mortality. Causes of death are indicated in Table 3. Comparisons between observed and expected mortality for each risk group are presented in Table 4.
Postoperative complications are listed in Table 5. One-hundred and seventy-nine patients (88%) were weaned from the ventilator and extubated within 24 h postoperatively. There was a 60% (122 patients) complications free rate.
4. Discussion
Advances in myocardial protection have been accompanied by a greater understanding of cardiac physiology and metabolism during ischemia and reperfusion. However, nobody can answer this question: "which is the best method of myocardial protection?". Why is it so difficult to highlight this best myocardial protection in the surgical practice? Probably because randomized prospective clinical trials comparing the use of different procedures of myocardial protection on prolonged aortic cross-clamping time do not exist. The efficacy of myocardial protection can be gauged to a large degree by the safe period of aortic occlusion that it affords the surgeon. Prolonged aortic cross-clamping time represents a rigorous test of the myocardial preservation. We have suggested that the term ‘long aortic cross-clamping time’ could be referred to time equal to or more than 150 min, depending on the few studies which reported this subject [4,5].
The effectiveness of the EuroSCORE has been demonstrated and allowed to compare the observed mortality rate to the expected one. Our study is not a randomized one. It describes the operative results of a historical cohort. Using intermediate lukewarm blood (20 °C) retrograde cardioplegia is the result of gradual evolution of the myocardial protection in our unit in the 1990s. We thought that it was not ethical to compare this technique to a crystalloid one or antegrade one because we suspected in a previous report that the cold crystalloid antegrade cardioplegia increases by four times the risk of perioperative myocardial infarction [3].
The induction of cardiac arrest by antegrade injection of hyperkalemic warm blood allows cardiac arrest in diastole and the restoration of high energy phosphate level [6]. The efficiency of myocardial protection obtained by retrograde cardioplegia had been demonstrated [7]. However, the disadvantage of retrograde cardioplegia remains a non-constant cardioplegic distribution to the interventricular septum and to the right ventricle [8]. It would be due to anatomical variations. The posterior interventricular vein which drains the left ventricular posterior wall as well as the posterior fourth of the interventricular septum [9], flows into the right atrium by the Thebesius veins in 13% of cases [9]. In these cases, the posterior fourth of the interventricular septum could not be well preserved by retrograde cardioplega. The small coronary vein which drains the right ventricle joins the coronary sinus in 40% of cases while in 60% of cases this vein drains into the right atrium or the right ventricle by the Thebesius veins [9]. In this condition, retrograde cardioplegia could not protect well the right ventricle. However, there was no postoperative septal or right ventricular infarction in our study. The protection of the posterior fourth of the interventricular septum and of the right ventricle was probably achieved by the venous network between the principal coronary veins [9] and by the cooling of intermediate lukewarm blood (20 °C) cardioplegia through the Thebesius vein. The superiority of blood cardioplegia on crystalloid cardioplegia had been demonstrated [10]. However, the temperature of blood cardioplegia remains a matter of controversy. Blood temperature between 20 and 25 °C seems to be the most appropriate [11]. Myocardial oxygen consumption is least during hyperkalemic arrest associated with moderate (22 °C) hypothermia [12]. High hypothermia (10 °C) increases blood viscosity and shifts the oxygen–hemoglobin dissociation curve leftward [13] while normothermia could not provide complete right ventricular preservation in the case of retrograde injection [14]. Continuous perfusion of blood cardioplegia can thus avoid myocardial ischemia eliminating the correlation between aortic cross-clamp time and ischemic time. The retrograde injection of warm blood enriched solution before removing the aortic clamp prevents reperfusion injury [15]. Finally, improving myocardial protection allows systemic normothermia, thus avoiding metabolic and hemodynamic effects of the hypothermia.
The observed operative mortality is similar to the series studied for long aortic cross-clamping time [4,5]. It remains close to the overall operative mortality in cardiac surgery. In-hospital mortality (Tables 3 and 5) was mainly related to non-cardiac causes (76%). They were probably more reliable for the patient-related factors rather than for the aortic cross-clamping time; 88% of the deaths occurred in patients of the high-risk group (Table 4). Comparison of the observed in-hospital mortality to the expected one, according to the EuroSCORE, has demonstrated that prolonged aortic clamping time with our myocardial protection does not aggravate operative mortality. This fact was not only established in the case of high risk patients but also in the case of low and medium risk patients. These results encourage us to perform extensive coronary artery reconstruction surgery [3], requiring longer cross aortic clamping time for low or medium risk patients.
The incidence of cardiac and non-cardiac-related complications (Table 5) did not seem to be different from the in-hospital morbidity associated with the usual cardiac surgery. In our study, the duration of post-operative mechanical ventilation is not expressed as a mean ± standard deviation for two reasons. Firstly, 7 patients had prolonged mechanical ventilation longer than 6 days which could increase the mean value. Secondly, fast-track cardiac anesthesia techniques were introduced gradually during the period of the study thus allowing early tracheal extubation. The patients operated during the last three years had the shortest duration of mechanical ventilation.
Continuous retrograde intermediate lukewarm undiluted blood cardioplegia associated with systemic normothermia allows prolonged aortic clamping time for complex intervention without increase of operative mortality and morbidity.
Acknowledgements
We would like to express our thanks to Fran?ois Roques, M.D., for help in comparing the observed operative mortality to the expected one calculated with the the EuroSCORE logistic method.
References
Kirklin JW. The science of cardiac surgery. Eur J Cardiothorac Surg 1990; 4:53–71.
Nashef SAM, Roques F, Michel P, Gauducheau E, Lemeshow S, Salamon R. the EuroSCORE study group. European system for cardiac operative risk evaluation (EuroSCORE). Eur J Cardiothorac Surg 1999; 16:9–13.
Barra JA, Bezon E, Mondine P, Resk A, Gilard M, Mansourati J, Boshat J. Surgical angioplasty with exclusion of atheromatous plaques in case of diffuse disease of the left anterior descending artery: 2 years' follow-up. Eur J Cardio-thorac Surg 2000; 17:509–514.
Bar-El Y, Adler Z, Kophit A, Kertzman V, Sawaed S, Ross A, Cohen O, Milo S. Myocardial protection in operations requiring more than 2 h of aortic cross-clamping. Eur J Cardiothorac Surg 1999; 15:271–275.
Chitwood WR Jr, Wixon CL, Norton TO, Lust RM. Complex valve operations: antegrade versus retrograde cardioplegia? Ann Thorac Surg 1995; 60:815–818.
Rosenkranz ER, Vinten-Johansen J, Buckberg GD, Okamoto F, Edwards H, Bugyi H. Benefits of normothermic induction of blood cardioplegia in energy-depleted hearts, with maintenance of arrest by multidose cold blood cardioplegia infusions. J Thorac Cardiovasc Surg 1982; 84:667–677.
Menasche P, Subayi JB, Veyssie L, Le Dref O, Chevret S, Piwnica A. Efficacy of coronary sinus cardioplegia in patients with complete coronary artery occlusions. Ann Thorac Surg 1991; 51:418–423.
Crooke GA, Harris LH, Grossi EA, Baumann FG, Galloway AC, Colvin SB. Biventricular distrubution of cold blood cardioplegic solution administered by different retrograde techniques. J Thorac Cardiovasc Surg 1991; 102:631–638.
Lüdinghausen MV. Nomenclature and distribution pattern of cardiac veins in man. In: Mohl W, Faxon D, Wolner E. eds. Clinics of CSI: 2nd International Symposium on Myocardial Protection in the Coronary Sinus 1986;New York: Springer-Verlag 13–32. In:.
Loop FD, Higgins TL, Panda R, Pearce G, Estafanous FG. Myocardial protection during cardiac operations. Decreased morbidity and lower cost with blood cardioplegia and coronary sinus perfusion. J Thorac Cardiovasc Surg 1992; 104:608–618.
Hayashida N, Weisel RD, Shirai T, Ikonomidis JS, Ivanov J, Carson SM, Mohabeer MK, Tumiati LC, Mickle DA. Tepid antegrade and retrograde cardioplegia. Ann Thorac Surg 1995; 59:723–729.
Buckberg GD, Brazier JR, Nelson RL, Goldstein SM, McConnell DH, Cooper N. Studies of the effects of hypothermia on regional myocardial blood flow and metabolism during cardiopulmonary bypass. I. The adequately perfused beating, fibrillating, and arrested heart. J Thorac Cardiovasc Surg 1977; 73:87–94.
Magovern Jr GJ, Flaherty JT, Gott VL, Bulkley BH, Gardner TJ. Failure of blood cardioplegia to protect myocardium at lower temperatures. Circulation 1982; 66:60–67.
Calderone CA, Krukenkamp IB, Misare BO. Perfusion deficits with retrograde warm blood cardioplegia. Ann Thorac Surg 1994; 57:403–406.
Julia PL, Buckberg GD, Acar C, Partington MT, Sherman MP. Studies of controlled reperfusion after ischemia. XXI. Reperfusate composition: superiority of blood cardioplegia over crystalloid cardioplegia in limiting reperfusion damage. Importance of endogenous oxygen free radical scavengers in red blood cells. J Thorac Cardiovasc Surg 1991; 101:303–313.(Eric Bezon, Jean No?l Cho)