Minimal Extracorporeal Circulation vs Off-Pump CABG
Abstract & Commentary
By Michael H. Crawford, MD
Source: Mazzei V, et al. Prospective randomized comparison of coronary bypass grafting with minimal extracorporeal circulation system (MECC) versus off-pump coronary surgery. Circulation. 2007;116:1761-1767.
Off-pump CABG avoids the complications of cardiopulmonary bypass (CPB), but is technically demanding. Thus, a minimal extracorporeal circulation (MEC) system was developed and has been shown to be superior to standard CPB. In this study, MEC is compared to off-pump CABG in 300 patients selected from 395 patients who were scheduled for elective CABG alone and were deemed candidates for either operative technique. Excluded were patients with single vessel disease and those with an inflammatory disease diagnosis. The operative technique was randomly assigned. The primary end point was release of biomarkers reflecting myocardial injury or an inflammatory state (CK, IL-6, S-100). All patients had a median sternotomy. The left internal thoracic artery was used for the left anterior descending artery and its branches, and saphenous veins were used for other vessels. Operative results and outcome at one year were also noted.
Results: In-hospital mortality was similar (MEC 1.4% vs 2% off-pump), and there were no significant differences in morbidity. Biomarkers were not significantly different, but there was a trend toward lower S-100 values off-pump (0.13 vs 0.19 pg/mL, P = 0.058). Length of stay and use of blood products were similar. Long-term outcomes were not significantly different. Mazzei and colleagues concluded that post-operative morbidity and mortality with MEC is comparable to off-pump. Consequently, MEC may achieve the benefits of off-pump, but permit more complete revascularization in patients not technically suitable for off-pump surgery.
Off-pump CABG is attractive, but complete revascularization is not always possible, and long-term studies have shown higher graft conclusion rates as compared to on-pump CABG. This study suggests that MEC may be an attractive option for patients not technically suitable for off-pump CABG. Tissue injury and inflammatory markers were not significantly different, although there was a trend toward lower S-100 levels, a presumed marker of brain injury with off-pump surgery. Clinical outcomes were also not different, but the study was underpowered for these end points.
MEC is a fully heparinized, short-closed loop circuit without a cardiotomy reservoir. This minimized blood contact with air and foreign surfaces. Blood is drained from the right atrium into a centrifugal pump and membrane oxygenator and then returned to the ascending aorta. A pericardial suction line is filtered, resulting in a cell saver type system that removes debris. Also, a cardioplegic arrest line is present. The system reduces systemic heparinization by 50% and reduces inflammatory cytokines to levels seen in off-pump cases. Inflammation is thought to be a major contributor to myocardial damage with CABG. There were no differences in strokes between the 2 techniques, but neuropsychologic testing was not performed.
After 50 years of use, CPB is being challenged by newer techniques that reduce the adverse effects of this device. At this point, the newer techniques have only been applied to selected patients because of their own limitations. As attractive as off-pump surgery seems, it is just not universally applicable if complete revascularization is the goal. Thus, MEC looks very attractive, as it reduces inflammatory and microembolic organ damage. However, it still requires manipulation of the ascending aorta, a potential source of macro cerebral emboli. Large studies will be required to fully assess clinical outcomes with MEC, but we may be at the threshold of a new safer way to operate on the heart.