Should off-pump CABG be abandoned?

J. Am. Coll. Cardiol. 2004;43:557-64

NO

Should off pump bypass be abandoned? Absolutely not, but let’s do it well.

The rationale for why off-pump CABG should be the preferred strategy is simple: cardiopulmonary bypass (CPB) entails extracorporeal circulation, aortic cannulation and clamping, global MI, hypothermia, and hemodilution, among other potentially deleterious phenomena. There are morbidities that can be attributed to these entities, and off-pump bypass avoids those effects by mechanically stabilizing each coronary artery target individually, while the rest of the heart beats and supports normal physiologic circulation. There is an important caveat to this, however, and that is if – and perhaps only if – a complete revascularization with precise anastomoses can be accomplished off pump, then the patient will in fact benefit.

At Emory University in Atlanta, we did a prospective, randomized trial on my own patients, which we called SMART (Surgical Management of Arterial Revascularization) trial. What we found was that in 200 unselected, consecutive patients undergoing either off- or on-pump CABG, we had lower myocardial enzyme release, fewer transfusions, more rapid extubation, and a shorter length of stay in hospital with off-pump CABG.

Completeness of revascularization is a very important issue. In SMART, the number of grafts per patient was exactly the same: 3.39 per patient with off-pump CABG and 3.4 with on-pump CABG. We coined the phrase "Index of Completeness of Revascularization," which we defined as the number of grafts we planned to do in examining the arteriogram prior to randomization and surgery divided by the number of grafts we actually did. We found no difference here, meaning we were able to do the operation we planned to do (1.00 vs. 1.01; P = not significant). Moreover, for the lateral wall, which is technically more difficult to reach in a beating heart, the number was similar in the off- and on-pump groups (0.97 vs. 0.98; P = not significant). We also used a similar percentage of arterial grafts in both groups.

CPB was an independent predictor of the need for transfusion by multivariate analysis with an odds ratio of 2.42 (P = .0073) and was associated with a longer length of stay by 1 day (5.1 days for off-pump and 6.1 for on-pump; P = .005 Wilcoxon).

Creatine phosphokinase of muscle band and troponin I release was about half as much in the off-pump group as in the on-pump group (P less than .001 Wilcoxon), and the rates of death, stroke, MI, angina, and reintervention were similar at both 30 days and 1 year, as was graft patency and quality of life. Off-pump CABG costs at 1 year were $1,955 less than on-pump, but this difference was not statistically significant (P = .08).

At 8 years, survival in SMART was still similar between groups (P = .33), as was graft patency in the small number of patients who had CT angiograms. PET scan results similarly showed no significant difference in ischemia between these two groups (P = .62). One patient in each group has had a percutaneous reintervention, and none have had a repeat coronary bypass in 10 years.

To see if these results could be replicated nationally, we turned to the STS database and looked at North American centers that performed more than 100 on-pump CABGs and more than 100 off-pump surgeries. This gave us 42,477 patients (16,245 off pump and 26,232 on pump) at 63 North American centers. We included the 2.2% of off-pump cases that were converted to on-pump cases in the off-pump group.

After risk adjustment for 32 variables, for the outcomes of death, stroke, MI, and major adverse cardiac events, off-pump bypass outperformed on-pump bypass in this huge cohort of patients from around the country. Looking at less-significant outcomes – renal failure, dialysis, sternal infection, reoperation, atrial fibrillation, prolonged ventilation, and length of stay greater than 14 days – all of them favored off-pump bypass.

We then looked at the Emory dataset (14,766 consecutive patients, 48% of whom had off-pump CABG and 52% on-pump) to see which patients benefitted more. For patients in the two lower quartiles of predicted risk, there was no difference in operative mortality. In the higher two risk quartiles, there was a mortality benefit with off-pump CABG, with a risk reduction for operative mortality of about 55% in the highest risk patients (P less than 0.001).

Logistic regression confirmed that there was an interaction between surgery type and predicted risk, and we now know that low-risk patients do not have the survival benefit of avoiding CPB. They do fine with on-pump CABG, but higher risk patients have a benefit from avoiding CPB and the higher the predicted risk, the greater the benefit to the patient.