Off-pump versus on-pump coronary artery bypass: does number of grafts performed represent a selection bias in comparative studies? Results from a matched cohort comparison.

Background: Several retrospective studies comparing off-pump and on-pump coronary surgery and the largest randomized studies published to date showed a lower number of grafts performed in patients submitted to off-pump coronary artery bypass surgery (OPCAB). These findings bring about the question of the general applicability of the results. We eliminated the selection bias correlated with the number of grafts per patient by comparing the short-term outcomes of patients undergoing OPCAB and standard coronary artery bypass grafting (CABG) matched for number of grafts.

Methods: Eighty-seven consecutive patients undergoing OPCAB (group A) were selected from the database of our Institution during a 2-year period. Matching was performed by iterative selection prioritizing, in the following sequence: number of grafts, EuroSCORE, and age. A total of 87 patients operated upon with the on-pump technique represented the control group (group B).

Results: There were no significant differences in preoperative characteristics between the two groups. The number of grafts per patient was 2.2 +/- 0.5 in group A and 2.2 +/- 0.5 in group B. Early mortality did not differ between the two groups and it was 2.2% (2 patients) in group A and 3.4% (3 patients) in group B (p = NS). The incidence of myocardial infarction did not differ between the two groups. No patient in either group had stroke or coma. Five (5.7%) patients in group A and 7 (8.0%) patients in group B had atrial fibrillation (p = NS).

Conclusions: We were unable to demonstrate any significant differences in short-term mortality or morbidity outcome between OPCAB and standard CABG patients Our findings suggest that excellent results can be obtained with both surgical approaches.