Thrombotic complications after valve replacement with porcine heterografts

Anticoagulation or antiplatelet therapy of bioprosthetic heart valves recipients: an unresolved issue

Improvements in the performance and longevity of biological valve prostheses have steadily increased their rates of implantation in recent years. Aortic bioprostheses, which are commonly used in the elderly or when the risks of anticoagulating are high, have generally been associated with low rates of long-term complications. Freedom from anticoagulation, therefore, represents the main theoretical advantage of biological, compared with mechanical, aortic prostheses. While a variety of anticoagulant and antiplatelet drug regimens have been described, a precise antithrombotic protocol for the early postoperative period after bioprosthetic aortic valve replacement has not been developed. There are also important differences between the international guidelines published. This review examines the clinical evidence concerning the use of vitamin K antagonist and antiplatelet therapy in the early management of the antithrombotic complications after bioprosthetic aortic valve replacement.

Comparing Warfarin With Aspirin After Biological Aortic Valve Replacement

Background— Patients with prosthetic heart valves have a higher risk of developing valve thrombosis and arterial thromboembolism. Antithrombotic therapy in the early postoperative period after biological aortic valve replacement (BAVR) is controversial. The American College of Cardiology/American Heart Association and European Society of Cardiology guidelines recommend the use of warfarin for the first 3 months after BAVR, although the American College Chest Physician guidelines suggest that the recommendations are very weak and that the risk/benefit is unclear. This prospective study investigated the efficacy of postoperative warfarin compared with aspirin in patients after aortic valve replacement.

Methods and Results— Patients undergoing BAVR between 2001 and 2002 received 2 antithrombotic therapies: 141 patients received warfarin for the first 3 months, and 108 patients received only aspirin. The major end points evaluated were the rate of cerebral ischemic events, bleeding, and survival. There were 3 and 5 postoperative cerebral ischemic events between 24 hours and 3 months for patients treated with aspirin and warfarin, respectively. After 3 months, the incidence of cerebral ischemic events did not differ between the 2 groups. The rate of major bleeding events, the stroke-free survival, and the overall survival rates were not statistically significant between the warfarin and aspirin groups.

Conclusions— There seem to be no advantages in performing early anticoagulation therapy compared with a low-antiplatelet regimen with regard to early cerebral ischemic events, bleeding, and survival. Currently there is no evidence to support the fact that warfarin is more effective than aspirin.

Heterograft valve replacement experience

Survey of implantation of porcine heterograft valves in the Dunedin Cardiac Surgical Unit has been reviewed covering 140 patients and 166 valves with a follow-up ranging from 1-55 months. The low mortality, minimal complication rate and absence of long term anticoagulants in the post operative regime are emphasized. Discussion centres on the low rate of complications and the usefulness of this valve. As with all biological valves durability is still in question.

Thromboembolic complications of current cardiac valvular prostheses

Thromboembolic complications associated with twelve different models of currently available aortic and mitral valve prostheses are reviewed. There is a need to standardize definitions of thrombotic phenomena and to report these events for valve model and anatomic location actuarially and in terms of incidence per 100 patient-years of follow-up. The incidence of thromboemboli is less than 2 per 100 patient-years for aortic biological valves without coumarin anticoagulation and for the best mechanical valves with coumarin. For mitral biological prostheses with and without coumarin, and for the best mechanical mitral valves with coumarin, the incidence approximates 4 per 100 patient years. The incidence of mortality and morbidity due to coumarin anticoagulation in patients with prosthetic valves is 0.17 and 2.2 per 100 patient-years, respectively. Omission, poor control or withdrawal of coumarin anticoagulation substantially increases the incidence of thromboemboli in patients with mechanical valves. Some reports suggest that the combination of dipyridamole and coumarin may further reduce thromboembolic complications without increasing bleeding problems. Atrial fibrillation clearly increases thromboembolic complications, but the importance of other factors such as atrial clot, large left atrial size, history of emboli, and first postoperative year is less definite.