Recurrence of thrombosis in patients with primary antiphospholipid syndrome: emphasis on arterial events.

OBJECTIVES

To assess risk factors for rethrombosis, the intensity and maintenance of anticoagulation in primary antiphospholipid syndrome (APS).

METHODS

We retrospectively included 81 patients with thrombotic APS under VKAs with ≥4 INR determinations per year in at least 1 year. We defined an index period as the time between the first available INR value and the next thrombotic event, or the time between the first and last available INR if rethrombosis-free. We recorded demographic and clinical/serologic variables, mean INR, mean INR-AUC, and anticoagulation intensity (INR<2.5, INR 2.5-3.5, and INR>3.5). For the statistical analysis we used Cox survival analysis, hazard function (H(t)) curves and AUC.

RESULTS

The median follow-up time was 6.4 years. 64 patients had no rethrombosis, whereas 17 did (15 arterial, 2 venous). The risk factors for rethrombosis were number of previous rethrombosis (RR 7.3 95% CI 2.3-322.7, p=0.007) and INR intensity (RR 0.03, 95% CI 0.002-0.367, p=0.001). Results were similar when only arterial events were analysed. At the H(t) curves, the cumulative risk was higher in patients with an INR <2.5 than those in an INR of 2.5-3.5. A mean INR of 2.2 identified patients at risk of rethrombosis (SE=0.82, SP=0.20, AUC=0.42).

CONCLUSIONS

The number of previous thrombotic events and the intensity of anticoagulation are rethrombosis risk factors. An INR ranging 2.5-3.5 protects against re-thrombosis, including arterial events.