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Of 77 University of Tokyo ventricular assist devices used in a total of 70 patients at 21 institutions, 13 pumps were found to have macroscopic thrombus formations. Because 19 devices that were used for less than 24 hours showed no thrombus deposition, they were considered not to have been sufficiently exposed to the thrombogenic environment for macroscopic thrombus deposition and were removed from the subsequent multivariate study. A total of eight potential risk factors were assessed in relation to thrombosis. Prevalences of thrombus formation were compared between two groups with or without each of the risk factors. In a univariate analysis, the following categoric variables were demonstrated to be significantly associated with complications, in descending order of significance: use of gabexate mesilate (protease inhibitor) as an anticoagulant (p = 0.005), normal platelet count (p = 0.010), duration of support (p = 0.038), leukocytosis (p = 0.042), and minimum pumping flow (p = 0.042). Use of heparin and the consequent increase in activated clotting time showed no relationship. Multivariate discriminant analysis, which was done to identify risk factors rejecting cross correlation between each variable, demonstrated platelet count (p = 0.006), use of gabexate mesilate (p = 0.007), and minimum flow (p = 0.008) to have significant and independent risks. These results indicate the importance of maintaining pumping flow above a certain minimum level, addition of antiplatelet drugs to the antithrombogenic regimen, and nonuse of gabexate mesitate.

A total of 61 VASs developed in Tokyo University were evaluated at 21 institutions in the period 1985-1989 for determination of its reliability and effectiveness. The system is comprised of a pneumatic sack-type pump (Nippon Zeon Co.), and its driving console (Aishin Seiki Co.). The stroke volume of the pump is 40 ml and blood contacting surfaces are coated with Cardiothane. Ages of the patients (pts) ranged from 12-82 yrs (mean 58 yrs). VASs were used in the assist mode of LVAD (54 pts), RVAD (5 pts) and BVAD (2 pts). Most of the cases (58 pts) included postocardiotomy cardiogenic shock after surgery for ischemic (28 pts), valvular (22 pts), both ischemic and valvular (7 pts) and congenital (1 pt) heart diseases. Average duration of the assist ranged from 1 hr-20 days (mean 5.6 dys). The VADs could be weaned in 34 cases (56%) and among these, 13 cases (21%) survived to discharge from the hospital. Causes of death in cases which could be weaned from the VAD included multiple organ failure/due to delayed institution of adequate circulatory support, renal failure and systemic infection. Small and minute thrombus formations were noted in 7 cases however, no pump originated thromboembolism were complicated. No troubles of the pump including leakage nor breakage, no mechanical failures of the driving consoles were experienced in any of the cases. Thus, it is concluded that the system was proved to be clinically effective and reliable.

We began applying of our VAD system clinically in 1982 and have subsequently obtained good results. The first case treated with the VAD returned to normal life. In a total of 70 cases of clinical applications this system there has been instance of apparatus dysfunction. Confirming the reliability and safety promised by the results of biological experiments. Here, we report the results of clinical application of the system in a total of 61 cases between August, 1985 and March, 1989. The following conclusions were reached: 1) Satisfactory weaning and survival rates were obtained i.e. 18 cases out of 61 cases (30%) survived over one month and 13 cases (21%) are currently surviving, even in elderly patients of 60 years of age or older. 2) The weaning rate and survival rates were good after approximately 1 week of support. Detailed evaluation of the recovery of the heart and functions of other major organs has led to the conclusion that the results can be improved further when the weaning period is carefully determined. 3) With regard to surgical factors, good findings were obtained when the artificial heart-lung bypass time was less than 6 hours. The VAD can be used in the early stages without vainly attempting weaning from the artificial heart-lung bypass. 4) There were no mechanical problems with the hardware of the blood pump drive assembly, etc., or noteworthy side effects.