Lower-intensity anticoagulation for mechanical heart valves: a new concept with the ATS bileaflet aortic valve. 
The design of the bileaflet ATS mechanical valve incorporates an open pivot at the hinge mechanism.  Total washout of blood at the pivot area seen using three-dimensional computational fluid dynamics modeling may make the valve less vulnerable for clot formation in patients without major thromboembolic risk factors.  Between January 1993 and June 1999, the ATS valve was implanted in the aortic position in 286 consecutive patients.  Patients were allocated prospectively to two groups: group 1 comprised patients in regular sinus rhythm with good left ventricular (LV) function (n = 144); group 2 included patients in non-sinus rhythm and/or with large hypocontractile left ventricles (n = 142).  The anticoagulation regime in group 1 was to achieve an INR of 1.5-2.5, rather than to maintain INR strictly at 2.5-3.5 for mechanical valves (as in group 2).  Follow up was 99% complete and ranged from 50 to 120 months.  Survival (Kaplan-Meier) was respectively 95% and 90% and 90% and 83% at 2 and 5 years in favor of group 1 (p = 0.0055).  Multivariate analysis selected advanced age, poor LV function and 'erratic' INR as risk factors for death.  Log rank analysis failed to detect any statistical difference in thromboembolism.  Bleeding occurred more frequently in group 2 (p = 0.018); independent risk factors for bleeding were the presence of aspirin (p = 0.0164) and advanced age (p = 0.02).  The excellent group 1 data and outcome encouraged continuation of the low-intensity anticoagulation regime, and should be regarded as a new concept for the treatment of mechanical valve patients.