Prevention of thromboembolism in patients with mitral stenosis and associated atrial fibrillation: effectiveness of low intensity (INR target 2) oral anticoagulant treatment.

Mitral stenosis (MS) in association with atrial fibrillation (AF) is a clinical condition at high risk for systemic thromboembolism. Although oral anticoagulants greatly reduce the incidence of thromboembolism in these patients, the optimal intensity of treatment has never been tested in specific clinical trials, and current recommendations are derived from studies of nonrheumatic AF. In this study we tested the effectiveness of two different intensities. The study design was carried out as an open randomized prospective study in an anticoagulation clinic. We randomized 103 patients with MS and AF to a low (target INR = 2) or moderate (target INR = 3) anticoagulation regimen. The primary end points were systemic thromboembolism, major bleeding and vascular death. During a mean follow-up of 4.5 years, 1 systemic embolism occurred in the low intensity group (0.41 per 100 pt/yrs, CI 0.01-2.3), and 1 minor stroke occurred in the moderate intensity group (0.40 per 100 pt/yrs, CI 0.01-2.3; p = ns). Major bleeding occurred in 8 patients, with 3 in the low intensity (1.25 per 100 pt/yrs) and 5 in the moderate intensity group (2.0 per 100 pt/yrs, Incidence Rate Ratio 0.6, CI 0.1-3.1; p = ns). Total events (systemic embolism, major bleeding and vascular death) occurred in 7 low intensity patients and 8 moderate intensity patients. As expected, minor bleeding was more frequent in the moderate intensity group of patients, who actually had more intense treatment and required closer monitoring of oral anticoagulant treatment. These data suggest that low intensity anticoagulation, as performed in an anticoagulation clinic, is effective and safe in high risk patients with MS and AF.

A comparison between six- and four-week intervals in surveillance of oral anticoagulant treatment.

We determined whether international normalized ratio (INR) monitoring at 6 weeks rather than 4 weeks would benefit patients and reduce costs. Patients receiving stable oral anticoagulation treatment (target INR, 3.0) with a prosthetic mechanical heart valve for more than 6 months were randomized for a maximum interval between INR determinations of 6 weeks (group 1, n = 59) or 4 weeks (group 2 [control], n = 65). Patients were followed up for 2 years. The primary end point of the study was the biologic risk of overanticoagulation or underanticoagulation, estimated as the rate of values at risk (INR, < 1.5 and > 5). The rates of INR values at risk for hemorrhagic (INR, > 5) or thromboembolic (INR, < 1.5) complications were 3.27% in group 1 and 3.09% in group 2 (P = .81). The INRs of patients in group 1 trended toward higher values, but no difference between groups was observed in time spent at various INR ranges by using the method of linear change. The mean time between INR determinations was 24.9 +/- 18.1 days (1.20 per month) in group 1 and 22.5 +/- 9.5 days (1.33 per month) in group 2 (P < .0003). For patients in stable condition with a prosthetic heart valve who are monitored at an anticoagulation clinic, a 6-week interval between INR determinations does not increase the biologic risk of thromboembolic or hemorrhagic events.