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ORIGINAL ARTICLE |
Section of Cardiac Surgery Department of Surgery, Washington Hospital Center Washington DC, USA
Jorge M Garcia, MD Tel: +1 202 291 1430 Fax: +1 202 291 1436 Email: Jorge.m.garcia{at}medstar.net, Section of Cardiac Surgery, Department of Surgery, Washington Hospital Center, 110 Irving Street NW, Suite 1E3, Washington DC 20010-2975, USA.
ABSTRACT
Outcomes of off-pump multivessel coronary artery bypass were compared with those of the on-pump procedure. From July 2001 to June 2006, 3,637 patients with multivessel coronary disease underwent off-pump coronary artery bypass, and 3,586 patients had on-pump coronary artery bypass in our center. The rates of operative mortality, permanent stroke, renal failure and perioperative myocardial infarction were significantly lower in the off-pump group, and these patients required fewer blood transfusions, shorter durations of ventilatory support, and shorter hospital stays. However, the patients who underwent on-pump coronary artery bypass were considered more high-risk and tended to have more complex procedures.
Key Words: Off-pump Coronary Artery Bypass
INTRODUCTION
Coronary artery bypass grafting (CABG) without cardiopulmonary bypass (CPB) has been performed for more than 20 years in our hospital.1–3 Although many studies have compared outcomes of off-pump coronary artery bypass (OPCAB) with on-pump CABG, no definitive conclusion has been reached regarding the benefits of OPCAB vs. on-pump CABG.4–8 Graft patency and incomplete revascularization have been the major concerns with the off-pump procedure. We report our experience of multivessel CABG in a recent 5-year period.
PATIENTS AND METHODS
Patients who underwent isolated off-pump and on-pump CABG with 2–10 grafts from July 1, 2001 to June 30, 2006 were included in this study. All preoperative, intraoperative, and postoperative data were collected, using the Society of Thoracic Surgeons’ definitions, in a computerized database registry in the Section of Cardiac Surgery, Washington Hospital Center. The Medstar Research Institute Review Board approved the study. The major clinical outcomes including operative mortality, perioperative myocardial infarction (MI), permanent stroke, transient stroke, and renal failure were analyzed.
All surgeons in our hospital have significant experience of on-pump and off-pump CABG, and the type of operation chosen was according to the individual surgeon’s preference. The indications for OPCAB comprised patients who were considered at high risk for on-pump CABG because of medical comorbidities such as renal failure, diffuse cerebrovascular and peripheral vascular disease, aortic arteriosclerosis, chronic obstructive pulmonary disease, and religious convictions that precluded blood transfusions. Contraindications to OPCAB included inadequate exposure and aberrant coronary artery anatomy such as poorly visualized target vessels on angiography, extremely small, heavily calcified, or extensively intramyocardial vessels. Preoperative hemodynamic instability was also a contra-indication to OPCAB.
Data are expressed as percentages, mean value ± standard deviation, or median and range. Continuous variables were compared using Student’s t test for normally distributed data and the Wilcoxon rank-sum test for nonparametric data. Dichotomous variables were compared via a chi-squared test of general association. Ordinal data were compared using the Cochran-Armitage test for trends. A p value of 0.05 or less was considered significant. All statistical analyses were performed with SAS for Windows version 9.1 (SAS Institute, Cary, NC, USA).
RESULTS
During the study period, 3,637 patients underwent OPCAB (50.4% of the CABG patient population; Figure 1
). The patients’ demographics, operative status, and risk factors are listed in Table 1. Patients who were smokers, diabetic, or obese were more likely to undergo on-pump CABG. Patients with left main coronary artery stenosis, MI within 24 h, preoperative cardiogenic shock, intraaortic balloon pump insertion, low left ventricular ejection fraction, and prior CABG were also more likely to undergo an on-pump procedure. OPCAB was more frequently performed in female and elderly patients (Table 1). The number of grafts per patient used in the on-pump CABG group was more than in the OPCAB group (Table 2). In patients requiring 2–3 grafts, OPCAB was performed more often, while in those requiring 4 or more grafts, on-pump CABG was the procedure of choice. Both procedures used similar arterial grafts, but the on-pump group used more saphenous vein grafts. The proportion of arterial grafts was significantly higher in the OPCAB group (Table 2). Figure 2 shows the usage of arterial grafts in both procedures during the study period. In 2001, fewer arterial grafts tended to be utilized in the OPCAB group than in the on-pump CABG group (44.3% vs. 47.2%, p > 0.1). During 2002 and 2003, the number of arterial grafts was similar in both groups. Since 2004, OPCAB has surpassed on-pump CABG in utilizing more arterial grafts. The number of saphenous vein grafts remained the same over these 5 years (Figure 3). On-pump CABG surgery utilized more saphenous vein grafts than OPCAB (p <0.001). Since 2002, the proportion of arterial grafts used in OPCAB has been significantly higher than in on-pump CABG (44.7% vs. 38.8%, p <0.001; Figure 4). The incidences of postoperative MI, stroke, renal failure, and operative mortality (in-hospital including 30 days after discharge) were significantly lower in OPCAB vs. on-pump CABG surgery. OPCAB was also associated with fewer blood transfusions in the perioperative period, and required shorter hospital stays (Table 3).
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In the mid 1980s, we started performing off-pump CABG in selected patients. We restricted this procedure to patients who needed grafts to the anterolateral coronaries or the right coronary artery. We also limited the procedure to those with certain comorbidities such as advanced age, calcified aorta, renal failure, severe cerebrovascular disease, and repeat surgery, as well as Jehovah’s Witnesses and other cases where the use of CPB might be contraindicated. Our 1985–1990 OPCAB data have been reported previously.1 Since the mechanical stabilizer was introduced into clinical practice in 1996, our percentage of OPCAB patients increased to 58.5% in 2002, and remained at 47%–50% over the next 5 years. According to the 2004–2007 Society of Thoracic Surgeons’ National Database, the national percentages of OPCAB volumes were 20.4%, 19.7%, and 19.1%, respectively.9 We reported the results of 220 OPCAB operations in 1992 and showed that OPCAB reduced blood product requirements and decreased the incidence of postoperative low cardiac output syndrome, but there was no significant difference in mortality compared with on-pump CABG.1 In 2002, with 3,322 OPCAB patients including more elderly, females, left main disease, chronic obstructive pulmonary disease, recent MI, and preoperative intraaortic balloon pumping, we found a lower incidence of major complications compared to on-pump CABG patients.2 These complications included perioperative MI, reoperation for bleeding, blood transfusion, prolonged ventilation, renal failure, length of hospital stay, and operative mortality. Age >80 years, cardiogenic shock, renal failure requiring dialysis, previous CABG, and low left ventricular ejection fraction were associated with higher mortality, controlling for CPB; CPB was independently associated with increased risk of operative mortality. In the current study, we found similar results when comparing risk variables between the 2 groups.
We have continued to demonstrate a lower postoperative stroke incidence associated with OPCAB compared to on-pump CABG throughout our 11 years of practice.10,11 Both our OPCAB and on-pump CABG stroke rates (1.1% vs. 2%) are consistent with those of other studies.5,12 We identified on-pump CABG surgery to be associated with a higher risk of early stroke. A new multicenter large-scale study found similar stroke rates for both procedures.5 Another large retrospective study compared more than 68,000 CABG patients and found significantly higher rates of stroke in the on-pump CABG groups.12 According to the Society of Thoracic Surgeons’ National Database, the predictive risk of mortality was 2.56% ± 4.24% for on-pump CABG vs. 2.14% ± 3.44% for OPCAB (p = 0.064).9 The mortality rates in our hospital are lower than in this for OPCAB, but higher for on-pump CABG. In reviewing recent reports, similar mortality rates for both procedures have been found in a risk-adjusted study, propensity-matched patients, prospective studies, and meta-analyses.12–17 The unadjusted mortality and high-risk patients’ mortality were significantly higher with on-pump CABG than with OPCAB.2,3,18,19
Incomplete revascularization by OPCAB has been a major concern for many years. Palmer and colleagues5 compared the number of vessels with at least one lesion occluded 
75% with the number of anastomoses performed. The ratio of anastomoses to vessels with lesions was 1.06 ± 0.44 in on-pump CABG and 1.02 ± 0.49 in OPCAB (p = 0.23). This indicates that the difference in numbers of grafts was a patient-selection issue and not due to incomplete revascularization. Sabik and colleagues14 at the Cleveland Clinic reviewed 812 propensity-matched patients with both procedures. The on-pump CABG group had more lesions bypassed and more complete revascularization than patients who underwent OPCAB. They found similar rates of operative mortality, stroke, and MI in both groups. The survival rates and freedom from MI and coronary re-intervention (3.8 vs. 2.6 years) for on-pump CABG and OPCAB were also not different. They concluded that mid-term outcomes with OPCAB and on-pump CABG were the same. According to our study, on-pump CABG patients received significantly more grafts than OPCAB patients (3.5 vs. 3.9), this difference arose mainly among those who received 4–6 grafts. Off-pump CABG patients received fewer grafts overall, but had a higher percentage of arterial grafts. Arterial grafts have better long-term patency than saphenous vein grafts; internal mammary artery grafts rarely develop arteriosclerosis. This is probably one of the reasons why OPCAB yields equal mid- and long-term outcomes to those of CABG.14 In addition, several studies compared the graft patency of both groups one year after surgery and also showed similar graft patency rates. As expected, the patency of saphenous vein grafts was lower than that of internal mammary artery grafts in both groups.20
In recent years, OPCAB has demonstrated better short-term outcomes in terms of atrial fibrillation, blood transfusion, and length of hospital stay in mixed-risk patient populations.6,20 OPCAB also improved mortality, morbidity, and resource utilization compared to on-pump CABG in high-risk patients.6,20 Our results are consistent with these studies. Our volume of OPCAB reached a plateau over these 5 years. Surgeon assessment of individual patients, surgeon training, hospital characteristics, patients’ consideration for both procedures, and other unmeasured variables could have influenced the choice of either OPCAB or on-pump CABG. Unfavorable coronary anatomy (diffuse, small, calcified, and deeply intramyocardial coronaries) may play a critical role in preoperative evaluation. Preoperative and intraoperative hemodynamic instability also may increase the rate of conversion from off-pump to on-pump CABG. Because our study was based on experience from a single institution, generalizing these results should be undertaken with caution. However, it was concluded that off-pump CABG yielded excellent outcomes, equal to those of on-pump CABG in our hospital. Outcomes depended more on patient characteristics than on the type of procedure. Operative complications and hospital mortality were reduced in the OPCAB group, including less usage of blood products and a shorter hospital stay.
REFERENCES
Asian Cardiovasc Thorac Ann 2009;
17:362-367
© 2009 by SAGE Publications
DOI: 10.1177/0218492309341710
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