Multivariate analysis of risk factors for thrombus formation in University of Tokyo ventricular assist device

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.