Antithrombogenicity of ventricular assist devices for postoperative myocardial dysfunction

Antithrombogenicity of pneumatic ventricular assist devices (VAD) for postoperative ventricular failure was evaluated macroscopically and microscopically in relation to VAD flow, coagulation parameters, and other potentially thrombogenic factors. A total of 12 sack type pumps were used in nine cases after operations for ischemic heart diseases (4 cases), valvular diseases (3 cases), and congenital anomalies (2 cases). Durations of pumping of each device ranged from 18 hours to 37 days (mean, 10.9 days). The clinical protocol for antithrombogenicity of the device indicates maintenance of ACT around 150 sec and keeping VAD flow more than 2.0 L/min. In our clinical series, however, heparin was given only in most cases to maintain activated clotting times (ACT) at 120-140 sec for the first three postoperative days. Minute ringlike thrombi were noted at connectors of cannula in two pumps after low flow (1.5 L/min) pumping for 5 days or after frequent on/off studies for weaning. A small thrombus (2 x 2 mm) and fine granular thrombi were noted on actuating bladders in two pumps that were used with frequent on/off studies or in a patient with severe sepsis during VAD pumping. Other VAD pumps were macroscopically free of thrombus. SEM analyses on surfaces of actuating bladders demonstrated mild to moderate platelet adhesions, which were correlated with platelet count, but not with other coagulation parameters including platelet agglutination and pumping duration. In cases with leucocytosis during VAD uses, leucocyte adhesion was noted as well without correlation to the coagulation parameters.