Claims that off-pump coronary artery bypass (OPCAB) carries a lower risk of short-term stroke than conventional on-pump coronary artery bypass grafting (CABG) have been the subject of contradicting evidence, mostly because of the small size of the studies that showed a benefit, but European investigators published a meta-analysis involving more than 19,000 cases that showed what they called a “significant reduction” in the odds of a stroke.
“OPCAB was associated with a significant (28%) reduction in the odds of stroke compared with CABG,” said lead author Dr. Mariusz Kowalewski of Copernicus University in Bydgoszcz, Poland, and coauthors. The meta-analysis appeared in the January issue of the Journal of Thoracic and Cardiovascular Surgery (2016;151:60-77).
The coauthors represent 10 different centers throughout Europe. Dr. Kowalewski and three other coauthors are also with the Systemic Investigation and Research on Interventions and Outcomes MEDICINE Research Network based in Düsseldorf, Germany.
Dr. Kowalewski and colleagues said this is the largest meta-analysis of randomized clinical trials comparing short-term outcomes of the two approaches to coronary bypass. “By its unique design, this analysis is the first report to investigate the causal relationship between underlying patient risk profile and the benefits of off-pump coronary revascularization,” they noted.
The meta-analysis looked at results of three primary outcomes: death within 30 days of the operation (2.25% overall, 2% in the OPCAB group and 2.04% in the CABG group); MI 30 days after surgery (4.49% overall, 4.3% for OPCAB and 4.67% for CABG); and 30-day occurrence of stroke (1.67% overall, 1.34% for OPCAB group and 2% for CABG).
In the meta-analysis, the researchers evaluated 100 studies for potential bias and conducted three separate analyses: one of all studies; and then separate analyses of studies of more than 50 and 100 subjects, respectively. Their goal was to check if small studies were driving the results.
Dr. Kowalewski and the study team acknowledged the conflicting science surrounding the benefits of the off-pump vs. conventional bypass. They pointed out that a host of randomized studies failed to show significant differences in stroke rates between the two approaches, and that conflicting European and American guidelines on the role of off-pump surgery to provide a better neurologic outcome do not help to clarify the relative risk.
“This apparent contradiction with the available registries’ data reporting a significantly decreased incidence of stroke with OPCAB may be explained by the fact that cerebral stroke represents a relatively rare entity after CABG, and thus even the largest randomized studies are underpowered to prove a possible advantage of one technique over the other,” Dr. Kowalewski and colleagues said.
They cited the CORONARY trial (N Engl J Med. 2012;366:1489-97), the largest trial to date, with 4,752 patients, which found no difference in the rate of stroke between the two groups. Three previous meta-analyses demonstrated 30%-50% reductions in stroke, but a systemic review called those results into question (Cochrane Database Syst. Rev. 2012;3:CD007224).
The “most important” finding of their study may be the confirmation of what large registries have reported: that OPCAB is safer and more effective than conventional bypass surgery in older and sicker patients. But they acknowledged that why this is the case “remains a subject of ongoing debate.”
Dr. Kowalewski and coresearchers acknowledged a number of limitations of their meta-analysis, namely that sensitivity analysis may have missed clinically important differences in patient results and broad patient inclusion criteria. However, the random-effects model they used accounted for study variations. “The findings on significant risk profile meta-regression are further corroborated in the analysis of MI and stroke,” they said.
Coauthor Dr. Eliano Pio Navarese disclosed honoraria from Eli Lilly. The other coauthors had no relationships to disclose.