Ten RCTs with a total of 4,180 patients were included in the review.
There was no indication of publication bias.
Four studies were rated as high quality and 6 studies as low quality.
Arterial thromboembolism (9 studies).
The incidence of arterial thromboembolism was significantly lower in the aspirin-OAC therapy group than in the OAC therapy alone group (OR 0.66, 95% CI. 0.52, 0.84). This represented an absolute risk reduction of 2.5% and a NNT to prevent one incident of 40. Statistically significant heterogeneity was detected (chi-squared 18.97, p0.02; I-squared 57.8%). An analysis using a random-effects model did not alter the results. Results from the sensitivity analysis, which included only high-quality studies, supported this finding. The subgroup analyses showed that a significant difference between the groups was only present for patients with a mechanical heart valve (OR 0.27, 95% CI: 0.15, 0.49).
Fatal arterial thromboembolism (9 studies).
There was no difference between the groups in the incidence of fatal arterial thromboembolism (OR 1.08, 95% CI: 0.76, 1.53).
Mortality (10 studies).
There was no significant difference between the groups in all-cause mortality (OR 0.98, 95% CI: 0.77, 1.25). No statistically significant heterogeneity was detected. Results from the sensitivity analysis, which included only high-quality studies, supported this finding. The subgroup analyses found no difference between the treatments in any patient group.
Major bleeding (10 studies).
The incidence of major bleeding was significantly higher in patients receiving combined aspirin OAC therapy than in those receiving OAC therapy alone (OR 1.43, 95% CI: 1.00, 2.02; absolute risk increase 1%; NNH 100). The sensitivity analysis, which included only high-quality studies, found no difference between the groups. The subgroup analyses demonstrated a significantly greater incidence of major bleeding only in patients with a mechanical heart valve.