Asian Cardiovasc Thorac Ann 2003;11:285-288
© 2003 Asia Publishing EXchange Ltd
Off-Pump Surgery: a Choice in Unstable Angina
Vijay Kohli, MCh,
Mukesh Goel, MCh,
Vijay Kumar Sharma, MCh,
Yugal Mishra, MD,
Rajneesh Malhotra, MCh,
Yatin Mehta, MD,
Naresh Trehan, MD
Escorts Heart Institute and Research Centre, New Delhi, India
For reprint information contact: Vijay Kohli, MCh Tel: 91 11 6825000 Fax: 91 11 6825013 email: vijay_K22{at}yahoo.com Escorts Heart Institute & Research Centre, Okhla Road, New Delhi – 110 025, India.
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ABSTRACT
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The benefit and safety of off-pump coronary artery bypass surgery in patients with unstable angina was assessed retrospectively. From February 1996 to October 2001, 5,306 patients underwent multivessel off-pump coronary artery bypass, of whom 920 (17%) had unstable angina. In these 920 patients, ejection fractions ranged from 15% to 70%, 203 (22%) had an ejection fraction of 20%–35%, and 11 (1%) had an ejection fraction < 20%. Triple-vessel disease was present in 625 patients. Preoperative intraaortic balloon pump support was used in 28 patients. Operative approaches included mid sternotomy (86%), lower partial sternotomy (9%), and left anterior thoracotomy (2%). The number of grafts ranged from 1 to 5 with a mean of 2.43 ± 0.86, and 92.3% of patients received a left internal mammary artery graft. Twenty-two patients need intraoperative intraaortic balloon pumping. Ten patients (1%) suffered perioperative myocardial infarction. The mean hospital stay was 7.8 ± 4.3 days. Hospital mortality was 2/920 (0.22%). Intraaortic balloon pumping was helpful in these cases of unstable angina refractory to medical therapy. Off-pump coronary artery surgery was found to be safe and beneficial in these patients.
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INTRODUCTION
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Unstable angina is one of the most common life-threatening medical emergencies. It may result in death or nonfatal myocardial infarction (MI) in up to 20% of patients within 30 days of an ischemic event. In the past, there has been considerable controversy regarding optimum treatment of this cardiac condition. Both conservative and invasive treatments of unstable angina are effective in reducing the risk of death or MI, but the FRISC II trial recommended invasive treatment.1 Technical advances in surgical procedures, anesthesia, and postoperative care have improved the results of surgery for unstable angina.2,3 Recently, the benefits of off-pump coronary artery bypass grafting (CABG) have been increasingly reported.4,5 Off-pump CABG was initially applied in cases requiring revascularization of 1 or 2 anterior vessels, but it has now been extended to treat all involved vessels.6 Off-pump CABG seems to be emerging as a safer alternative to conventional CABG, especially in high-risk cases such as redo surgery, advanced age, severe left ventricular (LV) dysfunction, and unstable angina.7 As previous studies have examined mixed groups of high-risk patients, this study was undertaken to assess the benefits of CABG without cardiopulmonary bypass (CPB) specifically in cases of unstable angina.
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PATIENTS AND METHODS
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From February 1996 to October 2001, 5,306 patients underwent isolated off-pump CABG at Escorts Heart Institute and Research Centre. Of these, 920 (17%) had unstable angina. The ages of these 920 patients varied from 29 to 88 years with a mean age of 59.15 ± 9.4 years. Other demographic and baseline characteristics are listed in Table 1
. Ejection fraction (EF) ranged from 15% to 70% with a mean EF of 47.46%; 11 patients (1%) had EF less than 20% and 203 (22%) had an EF of 20%–35%. Preoperative insertion of an intraaortic balloon pump (IABP) was required in 28 (3%) patients for intractable angina, hemodynamic instability, and electrocardiographic changes.
The operative approaches included a median sternotomy in 792 (86%) patients, a lower partial sternotomy in 83 (9%), and a left anterior thoracotomy in 15 (2%). Three patients had a lateral thoracotomy. A median sternotomy was used for multivessel revascularization. For single-vessel disease, a left anterior small thoracotomy was employed initially but it was later replaced by a lower partial sternotomy from the 3rd interspace to the xiphisternum, in order to bypass the left anterior descending artery. The Octopus II epicardial retraction device (Medtronic, Inc., Minneapolis, MN, USA) was used to stabilize the target vessel. For the posterior circumflex territory, 2–4 deep pericardial sutures were placed at the base of the heart, less than 1 cm from the pericardial reflection, interspersed in a fan-shaped arrangement between the left superior pulmonary vein and the inferior vena cava. The right pleura was widely opened to allow the heart to herniate through it during the procedure on the posterior circumflex territory. A Starfish suction device (Medtronic, Inc., Minneapolis, MN, USA) helped to maintain the heart in a vertical position without rotation of its base. This was found to be very useful for large dilated hearts with a low EF and hypertrophic hearts, which do not yield easily to conventional techniques. To maintain coronary perfusion, intracoronary shunts (Baxter Healthcare Corp., Irvine, CA, USA) were used for all vessels > 1.5 mm, except those that were diffusely diseased. Deteriorating hemodynamics prompted the use of an IABP or CPB, or both, to stabilize the patient and complete the revascularization. Adverse events such as intraoperative IABP use, perioperative MI, and conversion to on-pump surgery were noted. An adverse outcome was defined as prolonged intensive care unit (ICU) stay (> 4 days), prolonged inotropic or ventilatory support, hospital stay > 14 days, or hospital mortality.
Values are presented as mean ± standard deviation. Clinical data were compared by the two-sample t test, chi-squared test, or Fisher’s exact test, where appropriate. Multivariate analysis of the prediction of adverse outcome was carried out by logistic regression with backward selection of variables, using the Wald test at the 0.05 level. Statistical analysis was performed with SPSS version 10.0 software (SPSS, Inc., Chicago, IL, USA).
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RESULTS
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Details of grafts are given in Table 2. The mean number of grafts per patient was 2.43 ± 0.86. An IABP was inserted intraoperatively in 22 (2%) patients because of hemodynamic instability (low blood pressure, low cardiac output, high pulmonary arterial pressure, or arrhythmias). Perioperative MI occurred in 10 (1%) patients, detected by ST-segment changes on the electrocardiogram, a plasma creatine kinase-MB level of more than 50 U•L-1, and a new regional wall motion abnormality on echocardiography. Twenty (2%) patients had to be put on CPB during the course of revascularization, because of arrhythmias and rapid deterioration in hemodynamics. Univariate analysis of patient characteristics was performed for adverse events (Table 3). Redo surgery and low EF emerged as predictors of an adverse event. Further multivariate logistic regression analysis showed these two factors to be strong independent predictors of an adverse event (Table 4). Age, sex, history of previous or recent MI, congestive heart failure, hypertension, diabetes mellitus, left main stenosis, and the number and type of conduit had no effect on the occurrence of an adverse event. The ICU stay varied from 12 hours to 25 days with a mean of 48 hours. Hospital stay varied from 5 to 56 days with a mean of 7.8 ± 4.3 days. Older age (64.2 ± 9.2 vs. 58.9 ± 9.4 years), poor LV function (EF < 35%), redo surgery, and use of an IABP were found to be associated with longer ICU and hospital stays (Table 5). Multivariate logistic regression analysis revealed that age and IABP use were independent predictors of an adverse outcome (Table 6). Female sex and the presence of congestive heart failure tended to be associated with increased morbidity, but these findings were not statistically significant. History of past or recent MI, hypertension, diabetes mellitus, left main stenosis, number of grafts, or types of conduit were not associated with increased morbidity.
Two patients died in the hospital (mortality, 0.22%). One of these had poor LV function and was on IABP support preoperatively. The other patient had undergone an emergency operation with ischemic changes in the electrocardiogram, and had to be switched to on-pump surgery because of hemodynamic instability.
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DISCUSSION
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Off-pump CABG is easily adopted by surgeons conversant with CABG on CPB, without any adverse effect on the quality of anastomosis or a learning curve.8 An off-pump procedure has been noted to be particularly beneficial in high-risk patients such as redo cases, the elderly, and those with poor LV function.7 Off-pump CABG has been performed in our center since 1995, and from 1999, more than 90% of CABG patients have undergone surgery without CPB. In patients with unstable angina, CABG has been associated with higher risks than in those with stable coronary artery disease.9 Mortality rates of 1.2% to 8.5% (mean, 3.7%) have been reported, although safety has steadily improved due to better perioperative management.3 Aortic crossclamp time, age, perioperative MI, compromised LV function, urgent surgery, female gender, redo coronary operation, and left main stenosis are associated with a high risk of unstable angina requiring surgery.10,11 Off-pump CABG mitigates the effect of aortic crossclamping. Unstable angina acts as an ischemic preconditioning stimulus and lowers the extent of perioperative hemodynamic changes and myocardial enzyme release.12 The incidence of perioperative MI following CPB has been reported to be 3.5%.13 The low rate of 1% in this series is attributed to avoidance of global ischemia, use of intracoronary shunts, and maintenance of adequate perfusion pressure and cardiac output when rotating the heart for posterior revascularization. The use of an IABP has been noted to be beneficial during off-pump CABG.14 A preoperative IABP reduces myocardial ischemia, avoids progressive cardiac dysfunction, and minimizes low-flow episodes, thus improving the surgical outcome in high-risk patients. An intraoperative IABP maintains favorable hemodynamics during the cardiac manipulations required for posterior vessel anastomosis, and facilitates complete revascularization without CPB in high-risk patients.
The findings in this study generally agree with previous reports. Off-pump redo CABG was shown to be associated with higher early mortality than first-time CABG (12.5% vs. 3.4%).15 In this series, 13.6% of patients undergoing redo surgery needed an intraoperative IABP compared to 3.3% of first-time CABG patients. Furthermore, 10.4% of redo patients needed prolonged ICU and hospital stays compared to 3.2% of first-time patients. In reports comparing off-pump with on-pump redo CABG, the on-pump groups needed twice the postoperative transfusion volume and duration of ventilatory support compared to the off-pump groups.16,17 Older age emerged as a strong predictor of prolonged ICU and hospital stay. In elderly patients (> 70 years), off-pump CABG has been shown to result in reduced need for intraoperative transfusions, ventilatory support (1% vs. 12%), hospital stay, and incidence of atrial fibrillation compared to on-pump CABG.18 In this series, poor LV function (EF < 35%) resulted in increased use of an IABP perioperatively, but it did not prolong ICU or hospital stay. Increased perioperative mortality is associated with CABG in patients with poor LV function compared to those with normal LV function.19 Suboptimal outcomes in such cases might be due to the damaging effect of CPB on the myocardium. In addition, the change in LV geometry of the empty heart during CPB has been shown to impede the coronary collateral flow that supplies potentially ischemic areas of the myocardium. Cardiomegaly, frequently encountered in these patients, renders manipulation and rotation of the heart more difficult and potentially dangerous. Preoperative and intraoperative IABP use was very useful in these patients.
The risk factors in conventional CABG for unstable angina (left main disease, history of recent MI, and female gender) were found to be of no significance in our analysis.10,11 This is attributed to a combination of factors including avoidance of CPB and aortic crossclamping, timely use of an IABP, and improved perioperative management. Maintenance of adequate coronary perfusion pressure with inotropics (if needed) and use of intracoronary shunts have contributed to the low incidence of perioperative MI or conversion to CPB. It was concluded that these favorable results of off-pump CABG in patients with unstable angina were encouraging.
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ACKNOWLEDGMENTS
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We thank Mr. Sudhir Shekhawat for providing assistance in statistical analysis.
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ABSTRACT
INTRODUCTION
