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One-year coronary bypass graft patency: A randomized comparison between off-pump and on-pump surgery angiographic results of the PRAGUE-4 TrialWidimsky P, Straka Z, Stros P, et al. Circulation. 2004 Nov 30; 110(22):3418-23Reviewer: Mohammed Minhaj, MD
Abstract: Off-pump coronary bypass graft surgery (OPCABG) has become a widely used technique despite the overall limited availability of data regarding graft patency with this procedure. These investigators compared one-year angiographic patency of bypass grafts done off-pump, beating heart against those done classically (on-pump). Four hundred consecutive patients were randomized into two groups by cardiologists after they had clinical indications for cardiac bypass surgery. The surgeons involved could not initially exclude patients from randomization. Group A had classical on-pump surgery (n=192), group B had off-pump procedures (n=208). Of the 400 patients randomized, 388 eventually underwent operations (the other 12 either withdrew consent, were lost to follow-up prior to surgery or change in patient preferences, etc.) 255 patients had one-year follow-up angiography (132 from Group A, 123 from Group B); 127 patients refused follow-up, most of them citing the fact they felt well. There was no difference between the two groups of patients who returned for angiography in terms of age, sex, ejection fraction (EF), hypertension, diabetes or degree of disease (single vessel, double vessel, left main involvement, etc.) Surgeries were performed by one of four cardiac surgeons, all of whom had experience in the off-pump technique. Postoperative pharmacotherapy was not standardized but rather left up to the discretion of the patient's physician and there were no differences between the two groups in pharmacotherapy. Arterial graft patency after one year was 91% in both groups, while saphenous graft patency was 59% (on-pump) versus 49% (off-pump; P=NS). Saphenous graft patency per patient was lower in the off-pump group (0.7 patent anastomosis per patient versus 1.1 patent anastamosis in the on-pump group, P<0.01). Patients in Group A also had more mean distal anastamosis done per patient (2.7 vs. 2.3, P<0.001), more mean distal anastomoses patent per patient at one-year angiography (2.0 vs. 1.6, P<0.001) and more mean distal venous graft anastomoses patent at one-year angiography (1.1 vs. 0.7, P<0.01). Of the native coronary vessels bypassed, those involving the left anterior descending (LAD) artery were 100% patent versus only 23% on other arteries (P<0.0001). Despite these significant differences in patent grafts, both groups experienced similar, non-significant improvement in terms of function as measured by Canadian Cardiovascular Society Class. The authors conclude that the patency of arterial coronary bypass grafts done off-pump is excellent and equal to grafts done on-pump. However, the off-pump procedure results in fewer patent saphenous grafts per patient. Comments: Over the past decade, OPCABG surgical techniques have increased dramatically, with some experts predicting that nearly half of all bypass surgery will be done in this fashion within the next two years. Proponents of OPCABG tout its potential benefits versus traditional bypass surgery done with cardiopulmonary bypass (CPB). These proposed benefits include the reduction of the systemic inflammatory response, lower incidence of cognitive dysfunction, better myocardial preservation, reduced incidence of renal impairment, lower blood loss and transfusions, and potentially decreased hospital stay and cost. However, there still is insufficient data regarding long-term patency of grafts with OPCABG versus traditional surgery done with CPB. Previous studies are limited because patients were selected by surgeons for OPCABG techniques. This process introduces bias (such as the exclusion of patients for OPCABG based on low EF's, recent infarction, diffuse disease, etc.) into subsequent comparisons of results between patency of grafts done OPCABG versus on-pump CABG. The advantage of this study was that the randomization was performed by cardiologists, not surgeons, although the surgeon could change the plan preoperatively and intraoperatively if necessary. Preoperative crossover between patients in the off-pump and on-pump groups occurred in 5.4% of patients in each group (not significant), and intraoperative conversion from on-pump (Group A) to off-pump (Group B) was 1.1%. The intraoperative conversion from off-pump (Group B) to on-pump (Group A) was 9.8% (this was actually reported by the investigators in a previous publication regarding this database revolving around the surgical aspects of the study). While arterial graft patency was similar between the two groups, the study demonstrated a lower saphenous vein graft patency for both OPCABG and on-pump CABG patients than has been previously reported. The authors attributed this to the changing demographics of cardiac surgery patients. With the rise of interventional techniques, surgical patients are typically older, sicker, and have had previous therapeutic interventions. Their veins may be of poorer quality for bypass grafting. This is in contrast to previous studies on vein patency collected before the advent of coronary artery stenting. These patients typically were younger, with presumably higher quality coronary arteries and veins for the purpose of grafting. While not significant, the trend towards lower patency of saphenous vein grafts in the off-pump group, and the significantly lower number of distal anastamoses performed and lower number of patent distal anastamoses in the off-pump group, should at least warrant further investigation. Critics of off-pump techniques have pointed out it is technically more demanding, and as a result, the quality of the bypasses performed may suffer. The results in this study indicate that patency of vein grafts may be suboptimal, and may validate some of these arguments. Critics also point out there still is no data regarding long-term (>3 years) patency of grafts in off-pump surgery or improvement in terms of morbidity and mortality. In a recent meta-analysis comparing morbidity and mortality between OPCABG and traditional on-pump techniques, Cheng, et al, demonstrated that mortality, stroke, myocardial infarction, and renal failure were not reduced in OPCABG.1 An important limitation to the study was the large number of patients who did not report for follow-up angiography. While the authors state most of these patients had no symptoms and this could have negatively impacted overall patency rates, their exclusion should not have altered the final comparison conclusions between the two groups (as both groups would have benefited from more patients with presumably patent grafts). Overall, the study was well-designed, one of the few that is truly randomized, and important in examining the patency rates of OPCAG versus on-pump CABG. The role of OPCABG surgery continues to evolve, but there still exists a need for more evidence in support of the quality of bypasses in OPCABG as well as its potential reduction of complications associated with CPB in order to validate its continued growth. References
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