A practical approach for bridging anticoagulation after mechanical heart valve replacement

Following mechanical heart valve replacement, patients may require a form of 'bridging' anticoagulation to prevent valve-associated thromboembolism until oral vitamin K antagonists take effect. In 2000, the present authors changed their bridging protocol to a fixed dose of 40 mg enoxaparin twice daily (b.i.d., subcutaneous), regardless of the patient's body weight and renal function. The study aim was to evaluate the feasibility of this protocol with regards to thromboembolism, hemorrhage and other valve-associated adverse effects.

Between April 2000 and December 2004, a total of 256 consecutive patients who had undergone mechanical heart valve replacement were enrolled into this retrospective study. All patients received 40 mg enoxaparin b.i.d., subcutaneously, as bridging anticoagulation for a mean of 6.7 days, commencing at a mean of 3.8 days (range: 2-42 days) after surgery. This was approximately 55% (range: 32-95%) of the recommended dose considered to be safe in this setting.

A total of 18 (7%) minor bleeding events and two (0.7%) arterial thromboses were seen to arise from previously existing high-grade (>90%) stenosis of the affected vessels. At discharge, all prosthetic valves showed regular, echocardiographically confirmed, function. The mean follow up was 38.6 days (range: 8-106 days). Mitral valve replacement (p = 0.005) was shown to be a significant risk factor for minor bleeding, but not for thromboembolism. None of the other risk factors reached significance when testing for minor bleeding or major thromboembolic events.

Within the special setting of postoperative cardiac surgery, this modified anticoagulation protocol appears feasible and safe, with efficacy equivalent to that of full-dose protocols reported elsewhere using either low-molecular-weight or unfractionated heparin. By using this protocol, the effort required to bridge patients to effective oral anticoagulation was greatly reduced as there was no requirement for repeated laboratory measurements and dose adjustments. A prospective multi-center study should be conducted to confirm the hypothesis that the first bridging period after prosthetic heart valve replacement with extracorporeal circulation is different, and permits the use of a bridging protocol with a lower anticoagulation dose.