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Patients who undergo off-pump coronary artery bypass grafting (CABG) surgery experience nearly one-third fewer postoperative strokes than those who receive standard surgery using cardiopulmonary bypass. However, the 2 procedures yield similar rates of early mortality and myocardial infarction, according to an updated meta-analysis published online October 10, 2011, ahead of print in the European Heart Journal.

Jonathan Afilalo, MD, and colleagues at McGill University (Montreal, Canada) performed a meta-analysis of 59 randomized trials pulled from the medical literature and multiple databases through January 2011 that reported in-hospital or 30-day clinical outcomes. The pooled data comprised 8,961 patients randomized to off-pump (n = 4,461) or on-pump (n = 4,500) CABG. 

Stroke Protection Stands Out 

No difference was seen in rates of postoperative mortality or MI between the on- and off-pump groups. However, stroke occurred 30% less often in patients who underwent off-pump CABG (table 1).

Table 1. Postoperative Outcomes

In sensitivity analyses, the beneficial effect of off-pump bypass surgery on stroke was preserved after incorporating the trials with no events. In addition, the proportion of patients with a history of stroke did not affect the relative risk of post-CABG stroke.

In meta-regression analysis, the effect of both treatments on all clinical outcomes was similar regardless of mean age, proportion of women in the trial, number of grafts per patient for on- vs. off-pump surgery, and trial publication date.

According to the authors, the findings from this meta-analysis are bolstered by the fact that the pooled sample size is threefold larger than previously published meta-analyses, translating into greater statistical power and narrower confidence intervals.

Stroke Advantage Plausible 

The proposed ability of off-pump CABG to reduce stroke risk has been controversial, Dr. Avilalo and colleagues say, noting that even the largest randomized study to date, the ROOBY trial (Shroyer AL, et al. N Engl J Med. 2009;361:1827-1837), was underpowered to detect a difference in this infrequent event.

Nonetheless, they add, the multiple manipulations of the ascending aorta required by conventional bypass surgery, which promote embolization, provide a plausible mechanism for the increased stroke risk. Depending on the particular technique used, off-pump CABG eliminates 2 or 3 such manipulations, the investigators point out. 

The authors acknowledge a number of limitations. For one, their meta-regression technique, which reflects trial-level characteristics, is inferior to individual patient data for evaluating potential treatment interactions with patient factors. In addition, a considerable percentage of the underlying trials recorded no or few accrued clinical events or featured suboptimal ascertainment of events. This fact could have had a particular impact on stroke incidence, they add. Finally, differences in operative technique and surgeon volume could have influenced outcomes.  

Are Some Patients More Likely to Benefit Than Others? 

Nonetheless, “[g]iven the apparent reduction in stroke, the use of [off-pump CABG] should be pursued, especially in patients at higher risk of this complication,” the authors conclude, adding that factors such as aortic atheroma are promising candidates for predicting which patients will benefit most from the off-pump procedure. 

Robert A. Guyton, MD, of the Emory University School of Medicine (Atlanta, GA), agreed that this meta-analysis should prompt skeptical surgeons and cardiologists to reconsider the merits of off-pump surgery.

“The fact that this meta-analysis derives nearly one-quarter of its data from the ROOBY trial, which was fairly negative for off-pump CABG, and still ends up being supportive of off-pump surgery speaks well of the procedure,” he told TCTMD in a telephone interview.

Dr. Guyton added that although in this study patient subgroups were underpowered to detect a difference in treatment effect, experience at his own institution suggests that women and older patients in particular benefit from the off-pump strategy. 

Study Details

 The mean age was 63.4 years and the proportion of women was 16 ± 8%. The mean number of grafts was 2.8 ± 0.6 in the off-pump group and 3.0 ± 0.6 in the on-pump group, for a graft differential of -0.2 grafts.

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