Emergency conversion in off-pump coronary artery bypass grafting
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《血管的通路杂志》
Department of Cardiovascular Surgery, Shin-Tokyo Hospital, 473-1, Nemoto, Matsudo-Shi, Chiba 271-0077, Japan
Abstract
Emergency conversion to cardiopulmonary bypass in off-pump coronary artery bypass grafting is recognized to increase operative mortality and morbidity. We conducted a retrospective review of 616 consecutive patients who were planned for offpump coronary artery bypass grafting from April 2001 to July 2004. Fourteen patients (2.3%) required emergency conversion to cardiopulmonary bypass. Operative mortality was 13.3% in the conversion group and 1.2% in the non-conversion group (P<0.001). The incidence of reoperation for bleeding was 7.1% and 1.0%, respectively (P=0.032) and that of respiratory failure was 35.7% and 3.3%, respectively (P<0.001). Multivariable analysis showed that mitral regurgitation and chronic obstructive pulmonary disease were predictors of emergency conversion with all causes except for bleeding, and that mitral regurgitation and no use of a heart positioning device were predictors of emergency conversion due to hemodynamic compromise during distal anastomosis of the circumflex artery territory. In conclusion, emergency conversion in off-pump coronary artery bypass grafting increases operative mortality and morbidity. Mitral regurgitation and chronic obstructive pulmonary disease are risk factors for emergency conversion. Use of a heart positioning device decreases hemodynamic compromise during anastomosis of the circumflex artery territory.
Key Words: Coronary artery bypass surgery; Hemodynamics; Off-pump
1. Introduction
Off-pump coronary artery bypass grafting (OPCAB) has been shown to be a safe procedure with similar or better outcomes to conventional coronary artery bypass grafting (CABG). However, emergency conversion to cardiopulmonary bypass (CPB) is occasionally required due to hemodynamic compromise, bleeding and arrhythmias. It has been recognized to increase operative mortality and morbidity [1–4]. Identifying predictors of emergency conversion is essential to establish the safe indication of OPCAB as well as to improve the surgical and anesthetic techniques used to avoid emergency conversion. The aim of this study is to analyze outcomes and predictors of emergency conversion in OPCAB.
2. Materials and methods
2.1. Patients and data
Between April 2001 and June 2004, 616 consecutive patients were planned for OPCAB at our hospital. Six hundred and two patients (97.7%) underwent OPCAB without conversion and 14 patients (2.3%) required emergency conversion to CPB. All procedures were performed by a single experienced surgeon (S.T.). Anesthesia was exclusively managed by two experienced cardiac anesthesiologists in all cases. In-hospital outcomes were collected from patient medical records. Recent myocardial infarction (MI) was defined as an MI that occurred within 72 h prior to surgery. Previous MI was defined as MI that was not a recent MI. Postoperative renal insufficiency was defined as a new hemodialysis or hemofiltration. Respiratory failure was defined as pulmonary insufficiency requiring ventilatory support and any cases ventilated more than 48 h after surgery. The other variables were defined based on the Society of Thoracic Surgeons database definitions. Preoperative transthoracic echocardiography (TTE) was performed for all patients and the median duration between the echocardiographic examination and surgery was 4 days (range 0–32 days). Quantitative analysis was conducted by a single experienced echocardiographer and reviewed by cardiologists. The grade of mitral regurgitation (MR) was recorded as none, trivial, mild, moderate and severe (grades 0–4+, respectively). Intraoperative transesophageal echocardiography (TEE) was performed for all patients with more than mild MR on preoperative TTE and the severity of MR was reassessed. Preoperative, intraoperative and postoperative variables were compared between the conversion and non-conversion groups. Predictors of emergency conversion were determined with multivariable regression analysis.
2.2. Surgical procedures
OPCAB was performed through a median sternotomy. Deep pericardial sutures were used in our early experience before March 2001 (n=130). After that, the Starfish (Medtronic, Inc, Minneapolis, MN) was used to position the heart (n=486). Seven of 130 patients (5.4%) had emergency conversion before the introduction of the Starfish and 7 of 486 patients (1.4%) did since then (P=0.013). The Octopus III and IV (Medtronic, Inc, Minneapolis, MN) were used to stabilize the beating heart. A bloodless field of distal anastomosis was obtained with proximal silastic snare suture. A carbon dioxide blower was used for better visualization of target vessels. In most cases, the right coronary artery (RCA) territory was grafted first, which was followed by a circumflex artery and then left anterior descending artery (LAD) territories grafting. LAD was grafted first if the patient had a left main disease. Our indication of concomitant mitral valve repair for MR was severe MR on any echocardiographic study or moderate MR on intraoperative TEE.
2.3. Emergency conversion
We defined emergency conversion as a conversion to CPB after mobilization of the heart for anastomosis because of hypotension, hemorrhage, ischemia, critical arrhythmias (e.g. ventricular tachycardia/fibrillation) and cardiac arrest. Exclusions to the study were conversions related to difficult exposure of target vessels without evidence of hemodynamic compromise. The reasons of emergency conversion in 14 patietns are shown in Table 1. Two converted patients with bleeding were excluded from the multivariable analysis to determine the predictors of emergency conversion because bleeding is unpredictable.
2.4. Statistical analysis
Values of continuous variables were expressed as mean±standard deviation and/or median in case that the distribution of values is skewed. To analyze continuous variables we used the unpaired t-test. Chi-squared tests were used to analyze categorical variables. A logistic regression model was used to determine significant predictors of emergency conversion. Explanatory variables included all variables in Table 1 and the Starfish use, and they were selected with a backward stepwise method. A value of P was considered statistically significant when it was <0.05. Statistical analyses were performed with SPSS version 11.5J (SPSS, Inc, Chicago, IL).
3. Results
3.1. Preoperative characteristics
The mean age was 66.7±9.3 years. One hundred and fifty-five patients (25.2%) were women. On preoperative TTE, 91 patients (14.8%) had mild (2+) MR and 12 patients (1.9%) had moderate (3+) MR. All of these patients presented annular dilatation and/or leaflet tethering without prolapse, myxomatous change, chordal or papillary muscle rupture, vegetations and mitral stenosis. Preoperative patient characteristics are shown in Table 2.
3.2. Operative outcomes
The mean number of grafts was 3.6±1.4. Two hundred and twenty-one patients (35.9%) had a blood transfusion. Operative mortality was 1.5%. The mean length of intensive care unit (ICU) stay was 2.6±1.8 days.
There was no significant difference in the number of grafts and blood transfusion rates between the conversion and non-conversion groups. The complete revascularization index was 85.7% in the conversion group and 96.8% in the non-conversion group (P=0.023). Operative mortality was 14.3% in the conversion group and 1.2% in the non-conversion group (P<0.001). The incidence of reoperation for bleeding, respiratory failure and intraoperative/postoperative intra-aortic balloon pump (IABP) placement was significantly higher in the conversion group than non-conversion group. The mean length of ICU stay was significantly longer in the conversion group than the non-conversion group. Operative and postoperative variables are shown in Table 3.
3.3. Predictors of emergency conversion
Independent predictors of emergency conversion were mild to moderate MR (odds ratio [OR] 7.7 [95% confidence interval CI 2.3–25.5], P=0.001) and COPD (OR 7.0 [95%CI 1.3–38.3], P=0.024). Independent predictors of emergency conversion during anastomosis of the circumflex artery territory were mild to moderate MR (OR 5.7 [95%CI 1.3–25.4], P=0.024) and no use of the Starfish (OR 7.0 [95%CI 1.3–37.2], P=0.022).
4. Discussion
Conversion in OPCAB has been shown to increase mortality and morbidity, and operative mortality has been reported to range from 8.5 to 18% [1–4]. Some studies included elective conversions while others did not. Elective conversion without hemodynamic compromise has been reported not to increase mortality and morbidity [1,5]. In our emergently converted OPCAB group, the operative mortality was 14.3% and the incidence of respiratory failure and reoperation for bleeding was significantly higher than OPCAB without conversion. Two patients died from low output syndrome and multiple organ failure. Interestingly, the complete revascularization index was significantly lower than the non-conversion group, which might influence late outcomes.
Knowing predictors of emergency conversion is very important to establish the safe indication of OPCAB as well as to improve the surgical and anesthetic techniques used to avoid emergency conversion. Edgerton et al. showed that a surgeon who is early in experience of OPCAB techniques is an independent predictor of conversion [1]; a finding also confirmed by Soltoski and associates [5]. Although no study has shown that anesthetic skill is correlated to the incidence of conversion, it seems apparent that experienced anesthetic management is essential for successful OPCAB [6]. In our study, these biases were minimized since all surgical procedures and anesthetic managements were performed by a single experienced surgeon and two experienced anesthesiologists, respectively. Patel et al. concluded that emergency conversion is an unpredictable event and that the incidence of conversion decreases with increasing OPCAB experience of surgeons and use of the heart positioning device [3]. In our study, no use of a heart positioning device was an independent predictor of emergency conversion during anastomosis of the circumflex artery territory. Chang et al. have shown, in a randomized controlled study, that an apical suction device provides less hemodynamic compromise than the deep pericardial sutures during the exposure of the posterior descending artery and the obtuse marginal artery [7]. This finding has been also shown in other animal studies [8]. However, as Patel et al. [3] described, the reduction in the conversion after the introduction of a heart positioning device could also be due to the increasing experience of surgeons.
In our study, MR and COPD were independent predictors of emergency conversion with all causes except for bleeding. Intraoperative TEE showed an example of worsening MR during the dislocation of the heart (Fig. 1). George et al. supported this finding via TEE and showed distortion of the mitral annulus with enlargement of the left atrium and pulmonary veins while positioning the heart in OPCAB [9]. Omae et al. showed that MR worsened during left coronary artery anastomosis (most prominently during the circumflex artery territory anastomosis) and that patients with MR had more hemodynamic compromise (decreased cardiac index and increased mean pulmonary artery pressure) than those without MR during left coronary anastomosis. They also showed that milrinone was useful to stabilize hemodynamics for patients with MR [10]. Regarding COPD, pulmonary hypertension or poor oxygenation might contribute to hemodynamic compromise although we do not have those data.
Congestive heart failure [1,11], redo surgery [1], low EF [11], recent MI [11] have been reported to predict conversion although they were not significant predictors in our study. Furthermore, body mass index has been shown to predict conversion [4], intracoronary shunt use has been shown to reduce temporary hemodynamic compromise during the distal anastomosis in OPCAB [12], and coronary collaterals were reported to protect against perioperative MI in OPCAB [13]. These factors were not investigated in our study. Further investigation is needed to clarify the effect of these factors on emergency conversion.
Once knowing predictors of emergency conversion, how to prevent emergency conversion in high-risk patients should be considered. Elective on-pump CABG may be a good option when the risk of conversion outweighs the benefit of OPCAB. Otherwise prophylactic use of pharmacologic or mechanical support may be beneficial to avoid emergency conversion. Retrospective studies have shown that IABP is also a useful adjunct when trying to maintain hemodynamic stability in high-risk OPCAB patients [14]. Craver et al. have reported that elective IABP use for high-risk patients provided improved hemodynamic stability and eliminated the need for inotropic support during the dislocation of the heart in OPCAB [15]. In our study, preoperative IABP was not an independent predictor of emergency conversion. A randomized prospective study is needed to assess the effect of elective IABP placement on the avoidance of emergency conversion in OPCAB.
Additionally, judicious use of cardiac monitoring could provide an insight into predicting emergency conversion. Early changes in patient hemodynamics could be noticed before serious compromise and elective conversion could be chosen in such cases. Continuous myocardial pH monitoring, continuous mixed venous oxygen saturation monitoring or continuous wall motion monitoring with TEE might be beneficial for this purpose. Further investigation is required to know the effect of these monitoring interventions on the prevention of emergency conversion in OPCAB.
An important limitation of this study is that it is a retrospective study. Another limitation is the small patient number in the conversion group. A larger study is needed, but the bias of surgical and anesthetic skills should be adjusted even in large studies. The influence of emergency conversion on the late outcome needs to be investigated. We did not compare the outcomes between converted OPCAB and elective on-pump CABG because our number of elective CABG patients was low and selection bias was difficult to adjust for.
When considering the indication for OPCAB patients with mild to moderate ischemic MR, one has to consider not only the risk of conversion but also the need to perform a concomitant mitral valve repair; this remains controversial, so we have elected to omit it from this discussion. Currently we perform OPCAB in patients with mild to moderate MR if there is no indication of mitral valve repair (our indication for doing a concomitant mitral valve repair is outlined above); additionally, during the procedure we carefully monitor the pulmonary artery pressure, the severity of MR via a TEE and other vital parameters, and electively convert to CPB if they become worse.
In conclusion, emergency conversion to CPB increases operative mortality and morbidity in off-pump coronary artery bypass grafting. Mild to moderate MR and COPD are risk factors for emergency conversion. Use of a heart positioning device might decrease emergency conversion due to hemodynamic compromise during anastomosis in the circumflex artery territory.
References
Edgerton JR, Dewey TM, Magee MJ, Herbert MA, Prince SL, Jones KK, Mack MJ. Conversion in off-pump coronary artery bypass grafting: an analysis of predictors and outcomes. Ann Thorac Surg 2003; 76:1138–1143.
Calafiore AM, Mauro MD, Canosa C, Giammarco GD, Iacò AL, Continti M. Myocardial revasculariation with and without cardiopulmonary bypass: advantages, disadvantages and similarities. Eur J Cardiothorac Surg 2003; 24:953–960.
Patel NC, Patel NU, Loulmet DF, McCabe JC, Subramanian VA. Emergency conversion to cardiopulmonary bypass during attempted off-pump revascularization results in increased morbidity and mortality. J Thorac Cardiovasc Surg 2004; 128:655–661.
Legare JF, Buth KJ, Hirsch GM. Conversion to on pump from OPCAB is associated with increased mortality: results from a randomized controlled trial. Eur J Cardiothorac Surg 2005; 27:296–301.
Soltoski P, Salerno T, Levinsky L, Schmid S, Hasnain S, Diesfeld T, Huang C, Akhter M, Alnoweiser O, Bergsland J. Conversion to cardiopulmonary bypass in off-pump coronary artery bypass grafting. J Card Surg 1998; 13:328–334.
Michelsen LG, Horswell J. Anesthesia for off-pump coronary artery bypass grafting. Semin Thorac Cardiovasc Surg 2003; 15:71–82.
Chang WI, Kim KB, Kim JH, Ham BM, Kim YL. Hemodynamic changes during posterior vessel off-pump coronary artery bypass: comparison between deep pericardial sutures and vacuum-assisted apical suction device. Ann Thorac Surg 2004; 78:2057–2062.
Grundeman PF, Verlaan CW, van Boven WJ, Borst C. Ninety-degree anterior cardiac displacement in off-pump coronary artery bypass grafting: the Starfish cardiac positioner preserves stroke volume and arterial pressure. Ann Thorac Surg 2004; 78:679–684.
George SJ, Al-Ruzzeh S, Amrani M. Mitral annulus distortion during beating heart surgery: a potential cause for hemodynamic disturbance – a three-dimensional echocardiography reconstruction study. Ann Thorac Surg 2002; 73:1424–1430.
Omae T, Kakihana Y, Mastunaga A, Tsuneyoshi I, Kawasaki K, Kanmura Y, Sakata R. Hemodynamic changes during off-pump coronary artery bypass anastomosis in patients with coexisting mitral regurgitation: improvement with milrinone. Anesth Analg 2005; 101:2–8.
Mishra M, Shrivastava S, Dhar A, Bapna R, Mishra A, Meharwal ZS, Trehan N. A prospective evaluation of hemodynamic instability during off-pump coronary artery bypass surgery. J Cardiothorac Vasc Anesth 2003; 4:452–458.
Yeatman M, Caputo M, Narayan P, Ghosh AK, Ascione R, Ryder I, Angelini GD. Intracoronary shunts reduce transient intraoperative myocardial dysfunction during off-pump coronary operations. Ann Thorac Surg 2002; 73:1411–1417.
Nathoe HM, Buskens E, Jansen EW, Suyker WJ, Stella PR, Lahpor JR, van Boven WJ, van Dijk D, Diephuis JC, Borst C, Moons KG, Grobbee DE, de Jaegere PP. Role of coronary collaterals in off-pump and on-pump coronary bypass surgery. Circulation 2004; 110:1738–1742.
Suzuki T, Okabe M, Handa M, Yasuda F, Miyake Y. Usefulness of preoperative intraaortic balloon pump therapy during off-pump coronary artery bypass grafting in high-risk patients. Ann Thorac Surg 2004; 77:2056–2060.
Craver JM, Murrah P. Elective intraaortic balloon counterpulsation for high-risk off-pump coronary artery bypass operations. Ann Thorac Surg 2001; 71:1220–1223.(Minoru Tabata, Shuichiro )
Abstract
Emergency conversion to cardiopulmonary bypass in off-pump coronary artery bypass grafting is recognized to increase operative mortality and morbidity. We conducted a retrospective review of 616 consecutive patients who were planned for offpump coronary artery bypass grafting from April 2001 to July 2004. Fourteen patients (2.3%) required emergency conversion to cardiopulmonary bypass. Operative mortality was 13.3% in the conversion group and 1.2% in the non-conversion group (P<0.001). The incidence of reoperation for bleeding was 7.1% and 1.0%, respectively (P=0.032) and that of respiratory failure was 35.7% and 3.3%, respectively (P<0.001). Multivariable analysis showed that mitral regurgitation and chronic obstructive pulmonary disease were predictors of emergency conversion with all causes except for bleeding, and that mitral regurgitation and no use of a heart positioning device were predictors of emergency conversion due to hemodynamic compromise during distal anastomosis of the circumflex artery territory. In conclusion, emergency conversion in off-pump coronary artery bypass grafting increases operative mortality and morbidity. Mitral regurgitation and chronic obstructive pulmonary disease are risk factors for emergency conversion. Use of a heart positioning device decreases hemodynamic compromise during anastomosis of the circumflex artery territory.
Key Words: Coronary artery bypass surgery; Hemodynamics; Off-pump
1. Introduction
Off-pump coronary artery bypass grafting (OPCAB) has been shown to be a safe procedure with similar or better outcomes to conventional coronary artery bypass grafting (CABG). However, emergency conversion to cardiopulmonary bypass (CPB) is occasionally required due to hemodynamic compromise, bleeding and arrhythmias. It has been recognized to increase operative mortality and morbidity [1–4]. Identifying predictors of emergency conversion is essential to establish the safe indication of OPCAB as well as to improve the surgical and anesthetic techniques used to avoid emergency conversion. The aim of this study is to analyze outcomes and predictors of emergency conversion in OPCAB.
2. Materials and methods
2.1. Patients and data
Between April 2001 and June 2004, 616 consecutive patients were planned for OPCAB at our hospital. Six hundred and two patients (97.7%) underwent OPCAB without conversion and 14 patients (2.3%) required emergency conversion to CPB. All procedures were performed by a single experienced surgeon (S.T.). Anesthesia was exclusively managed by two experienced cardiac anesthesiologists in all cases. In-hospital outcomes were collected from patient medical records. Recent myocardial infarction (MI) was defined as an MI that occurred within 72 h prior to surgery. Previous MI was defined as MI that was not a recent MI. Postoperative renal insufficiency was defined as a new hemodialysis or hemofiltration. Respiratory failure was defined as pulmonary insufficiency requiring ventilatory support and any cases ventilated more than 48 h after surgery. The other variables were defined based on the Society of Thoracic Surgeons database definitions. Preoperative transthoracic echocardiography (TTE) was performed for all patients and the median duration between the echocardiographic examination and surgery was 4 days (range 0–32 days). Quantitative analysis was conducted by a single experienced echocardiographer and reviewed by cardiologists. The grade of mitral regurgitation (MR) was recorded as none, trivial, mild, moderate and severe (grades 0–4+, respectively). Intraoperative transesophageal echocardiography (TEE) was performed for all patients with more than mild MR on preoperative TTE and the severity of MR was reassessed. Preoperative, intraoperative and postoperative variables were compared between the conversion and non-conversion groups. Predictors of emergency conversion were determined with multivariable regression analysis.
2.2. Surgical procedures
OPCAB was performed through a median sternotomy. Deep pericardial sutures were used in our early experience before March 2001 (n=130). After that, the Starfish (Medtronic, Inc, Minneapolis, MN) was used to position the heart (n=486). Seven of 130 patients (5.4%) had emergency conversion before the introduction of the Starfish and 7 of 486 patients (1.4%) did since then (P=0.013). The Octopus III and IV (Medtronic, Inc, Minneapolis, MN) were used to stabilize the beating heart. A bloodless field of distal anastomosis was obtained with proximal silastic snare suture. A carbon dioxide blower was used for better visualization of target vessels. In most cases, the right coronary artery (RCA) territory was grafted first, which was followed by a circumflex artery and then left anterior descending artery (LAD) territories grafting. LAD was grafted first if the patient had a left main disease. Our indication of concomitant mitral valve repair for MR was severe MR on any echocardiographic study or moderate MR on intraoperative TEE.
2.3. Emergency conversion
We defined emergency conversion as a conversion to CPB after mobilization of the heart for anastomosis because of hypotension, hemorrhage, ischemia, critical arrhythmias (e.g. ventricular tachycardia/fibrillation) and cardiac arrest. Exclusions to the study were conversions related to difficult exposure of target vessels without evidence of hemodynamic compromise. The reasons of emergency conversion in 14 patietns are shown in Table 1. Two converted patients with bleeding were excluded from the multivariable analysis to determine the predictors of emergency conversion because bleeding is unpredictable.
2.4. Statistical analysis
Values of continuous variables were expressed as mean±standard deviation and/or median in case that the distribution of values is skewed. To analyze continuous variables we used the unpaired t-test. Chi-squared tests were used to analyze categorical variables. A logistic regression model was used to determine significant predictors of emergency conversion. Explanatory variables included all variables in Table 1 and the Starfish use, and they were selected with a backward stepwise method. A value of P was considered statistically significant when it was <0.05. Statistical analyses were performed with SPSS version 11.5J (SPSS, Inc, Chicago, IL).
3. Results
3.1. Preoperative characteristics
The mean age was 66.7±9.3 years. One hundred and fifty-five patients (25.2%) were women. On preoperative TTE, 91 patients (14.8%) had mild (2+) MR and 12 patients (1.9%) had moderate (3+) MR. All of these patients presented annular dilatation and/or leaflet tethering without prolapse, myxomatous change, chordal or papillary muscle rupture, vegetations and mitral stenosis. Preoperative patient characteristics are shown in Table 2.
3.2. Operative outcomes
The mean number of grafts was 3.6±1.4. Two hundred and twenty-one patients (35.9%) had a blood transfusion. Operative mortality was 1.5%. The mean length of intensive care unit (ICU) stay was 2.6±1.8 days.
There was no significant difference in the number of grafts and blood transfusion rates between the conversion and non-conversion groups. The complete revascularization index was 85.7% in the conversion group and 96.8% in the non-conversion group (P=0.023). Operative mortality was 14.3% in the conversion group and 1.2% in the non-conversion group (P<0.001). The incidence of reoperation for bleeding, respiratory failure and intraoperative/postoperative intra-aortic balloon pump (IABP) placement was significantly higher in the conversion group than non-conversion group. The mean length of ICU stay was significantly longer in the conversion group than the non-conversion group. Operative and postoperative variables are shown in Table 3.
3.3. Predictors of emergency conversion
Independent predictors of emergency conversion were mild to moderate MR (odds ratio [OR] 7.7 [95% confidence interval CI 2.3–25.5], P=0.001) and COPD (OR 7.0 [95%CI 1.3–38.3], P=0.024). Independent predictors of emergency conversion during anastomosis of the circumflex artery territory were mild to moderate MR (OR 5.7 [95%CI 1.3–25.4], P=0.024) and no use of the Starfish (OR 7.0 [95%CI 1.3–37.2], P=0.022).
4. Discussion
Conversion in OPCAB has been shown to increase mortality and morbidity, and operative mortality has been reported to range from 8.5 to 18% [1–4]. Some studies included elective conversions while others did not. Elective conversion without hemodynamic compromise has been reported not to increase mortality and morbidity [1,5]. In our emergently converted OPCAB group, the operative mortality was 14.3% and the incidence of respiratory failure and reoperation for bleeding was significantly higher than OPCAB without conversion. Two patients died from low output syndrome and multiple organ failure. Interestingly, the complete revascularization index was significantly lower than the non-conversion group, which might influence late outcomes.
Knowing predictors of emergency conversion is very important to establish the safe indication of OPCAB as well as to improve the surgical and anesthetic techniques used to avoid emergency conversion. Edgerton et al. showed that a surgeon who is early in experience of OPCAB techniques is an independent predictor of conversion [1]; a finding also confirmed by Soltoski and associates [5]. Although no study has shown that anesthetic skill is correlated to the incidence of conversion, it seems apparent that experienced anesthetic management is essential for successful OPCAB [6]. In our study, these biases were minimized since all surgical procedures and anesthetic managements were performed by a single experienced surgeon and two experienced anesthesiologists, respectively. Patel et al. concluded that emergency conversion is an unpredictable event and that the incidence of conversion decreases with increasing OPCAB experience of surgeons and use of the heart positioning device [3]. In our study, no use of a heart positioning device was an independent predictor of emergency conversion during anastomosis of the circumflex artery territory. Chang et al. have shown, in a randomized controlled study, that an apical suction device provides less hemodynamic compromise than the deep pericardial sutures during the exposure of the posterior descending artery and the obtuse marginal artery [7]. This finding has been also shown in other animal studies [8]. However, as Patel et al. [3] described, the reduction in the conversion after the introduction of a heart positioning device could also be due to the increasing experience of surgeons.
In our study, MR and COPD were independent predictors of emergency conversion with all causes except for bleeding. Intraoperative TEE showed an example of worsening MR during the dislocation of the heart (Fig. 1). George et al. supported this finding via TEE and showed distortion of the mitral annulus with enlargement of the left atrium and pulmonary veins while positioning the heart in OPCAB [9]. Omae et al. showed that MR worsened during left coronary artery anastomosis (most prominently during the circumflex artery territory anastomosis) and that patients with MR had more hemodynamic compromise (decreased cardiac index and increased mean pulmonary artery pressure) than those without MR during left coronary anastomosis. They also showed that milrinone was useful to stabilize hemodynamics for patients with MR [10]. Regarding COPD, pulmonary hypertension or poor oxygenation might contribute to hemodynamic compromise although we do not have those data.
Congestive heart failure [1,11], redo surgery [1], low EF [11], recent MI [11] have been reported to predict conversion although they were not significant predictors in our study. Furthermore, body mass index has been shown to predict conversion [4], intracoronary shunt use has been shown to reduce temporary hemodynamic compromise during the distal anastomosis in OPCAB [12], and coronary collaterals were reported to protect against perioperative MI in OPCAB [13]. These factors were not investigated in our study. Further investigation is needed to clarify the effect of these factors on emergency conversion.
Once knowing predictors of emergency conversion, how to prevent emergency conversion in high-risk patients should be considered. Elective on-pump CABG may be a good option when the risk of conversion outweighs the benefit of OPCAB. Otherwise prophylactic use of pharmacologic or mechanical support may be beneficial to avoid emergency conversion. Retrospective studies have shown that IABP is also a useful adjunct when trying to maintain hemodynamic stability in high-risk OPCAB patients [14]. Craver et al. have reported that elective IABP use for high-risk patients provided improved hemodynamic stability and eliminated the need for inotropic support during the dislocation of the heart in OPCAB [15]. In our study, preoperative IABP was not an independent predictor of emergency conversion. A randomized prospective study is needed to assess the effect of elective IABP placement on the avoidance of emergency conversion in OPCAB.
Additionally, judicious use of cardiac monitoring could provide an insight into predicting emergency conversion. Early changes in patient hemodynamics could be noticed before serious compromise and elective conversion could be chosen in such cases. Continuous myocardial pH monitoring, continuous mixed venous oxygen saturation monitoring or continuous wall motion monitoring with TEE might be beneficial for this purpose. Further investigation is required to know the effect of these monitoring interventions on the prevention of emergency conversion in OPCAB.
An important limitation of this study is that it is a retrospective study. Another limitation is the small patient number in the conversion group. A larger study is needed, but the bias of surgical and anesthetic skills should be adjusted even in large studies. The influence of emergency conversion on the late outcome needs to be investigated. We did not compare the outcomes between converted OPCAB and elective on-pump CABG because our number of elective CABG patients was low and selection bias was difficult to adjust for.
When considering the indication for OPCAB patients with mild to moderate ischemic MR, one has to consider not only the risk of conversion but also the need to perform a concomitant mitral valve repair; this remains controversial, so we have elected to omit it from this discussion. Currently we perform OPCAB in patients with mild to moderate MR if there is no indication of mitral valve repair (our indication for doing a concomitant mitral valve repair is outlined above); additionally, during the procedure we carefully monitor the pulmonary artery pressure, the severity of MR via a TEE and other vital parameters, and electively convert to CPB if they become worse.
In conclusion, emergency conversion to CPB increases operative mortality and morbidity in off-pump coronary artery bypass grafting. Mild to moderate MR and COPD are risk factors for emergency conversion. Use of a heart positioning device might decrease emergency conversion due to hemodynamic compromise during anastomosis in the circumflex artery territory.
References
Edgerton JR, Dewey TM, Magee MJ, Herbert MA, Prince SL, Jones KK, Mack MJ. Conversion in off-pump coronary artery bypass grafting: an analysis of predictors and outcomes. Ann Thorac Surg 2003; 76:1138–1143.
Calafiore AM, Mauro MD, Canosa C, Giammarco GD, Iacò AL, Continti M. Myocardial revasculariation with and without cardiopulmonary bypass: advantages, disadvantages and similarities. Eur J Cardiothorac Surg 2003; 24:953–960.
Patel NC, Patel NU, Loulmet DF, McCabe JC, Subramanian VA. Emergency conversion to cardiopulmonary bypass during attempted off-pump revascularization results in increased morbidity and mortality. J Thorac Cardiovasc Surg 2004; 128:655–661.
Legare JF, Buth KJ, Hirsch GM. Conversion to on pump from OPCAB is associated with increased mortality: results from a randomized controlled trial. Eur J Cardiothorac Surg 2005; 27:296–301.
Soltoski P, Salerno T, Levinsky L, Schmid S, Hasnain S, Diesfeld T, Huang C, Akhter M, Alnoweiser O, Bergsland J. Conversion to cardiopulmonary bypass in off-pump coronary artery bypass grafting. J Card Surg 1998; 13:328–334.
Michelsen LG, Horswell J. Anesthesia for off-pump coronary artery bypass grafting. Semin Thorac Cardiovasc Surg 2003; 15:71–82.
Chang WI, Kim KB, Kim JH, Ham BM, Kim YL. Hemodynamic changes during posterior vessel off-pump coronary artery bypass: comparison between deep pericardial sutures and vacuum-assisted apical suction device. Ann Thorac Surg 2004; 78:2057–2062.
Grundeman PF, Verlaan CW, van Boven WJ, Borst C. Ninety-degree anterior cardiac displacement in off-pump coronary artery bypass grafting: the Starfish cardiac positioner preserves stroke volume and arterial pressure. Ann Thorac Surg 2004; 78:679–684.
George SJ, Al-Ruzzeh S, Amrani M. Mitral annulus distortion during beating heart surgery: a potential cause for hemodynamic disturbance – a three-dimensional echocardiography reconstruction study. Ann Thorac Surg 2002; 73:1424–1430.
Omae T, Kakihana Y, Mastunaga A, Tsuneyoshi I, Kawasaki K, Kanmura Y, Sakata R. Hemodynamic changes during off-pump coronary artery bypass anastomosis in patients with coexisting mitral regurgitation: improvement with milrinone. Anesth Analg 2005; 101:2–8.
Mishra M, Shrivastava S, Dhar A, Bapna R, Mishra A, Meharwal ZS, Trehan N. A prospective evaluation of hemodynamic instability during off-pump coronary artery bypass surgery. J Cardiothorac Vasc Anesth 2003; 4:452–458.
Yeatman M, Caputo M, Narayan P, Ghosh AK, Ascione R, Ryder I, Angelini GD. Intracoronary shunts reduce transient intraoperative myocardial dysfunction during off-pump coronary operations. Ann Thorac Surg 2002; 73:1411–1417.
Nathoe HM, Buskens E, Jansen EW, Suyker WJ, Stella PR, Lahpor JR, van Boven WJ, van Dijk D, Diephuis JC, Borst C, Moons KG, Grobbee DE, de Jaegere PP. Role of coronary collaterals in off-pump and on-pump coronary bypass surgery. Circulation 2004; 110:1738–1742.
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