Mechanical Ventricular Assistance Rescues Endocardial Thrombomodulin Expression and May Restore Thromboresistance.

Heart failure is associated with a significant risk for thrombosis and an increased risk for thromboembolic events. Disturbance in blood flow, endothelial dysfunction or injury, and a hypercoagulable state are each present in heart failure and may contribute to the prothrombotic milieu. More recent evidence has linked heart failure with an active thrombogenic state, as demonstrated by elevated levels of thrombin-antithrombin complexes, prothrombin fragment F1+2, and fibrinopeptide A, all indices of thrombin activation. Thrombomodulin (TM), an integral membrane protein found on the endocardial endothelium (EE), is a potent thrombin inhibitor via activation of the protein C pathway. We hypothesized that the loss of thromboresistance on the ventricular endocardium, which has previously been described in cardiomyopathy, would be restored by placement of a temporary ventricular assistance device (VAD). Using left ventricular apical tissue obtained from heart failure subjects (CHF) undergoing a VAD as a bridge to heart transplant (n=4), and then from apical tissue of the same subjects at the time of explantation (post-VAD), we quantified TM protein expression using an anti-human TM antibody on EE by digital immunohistochemical analysis. TM expression levels were expressed as arbitrary units (AU) reaching signal intensity threshold per millimeter (mm) of left ventricular (LV) perimeter (AU/mm). Control TM staining of LV endocardial segments (n=2) obtained from the apex of normal hearts not used for transplantation after being excised from potential donors was 1482 and 1587 AU/mm (avg=1534 AU/mm). In CHF cardiac tissue obtained at the time of VAD placement (pre-VAD), TM protein expression on the ventricular EE of the LV apex was markedly decreased compared to control (275±67 AU/mm, p<0.01 vs. control LV, using unpaired t-test). Endocardial TM protein expression returned to near baseline levels (1182±32 AU/mm) in post-VAD cardiac samples explanted at the time of transplant from the same subjects (following VAD placement of 1–4 months in all subjects). The post-VAD TM level represented a highly significant rise over pre-VAD TM level (p<0.01 using paired t-test). Persistent staining of adjacent tissue sections in all cardiac samples for von Willebrand factor, an endothelial marker, provided clear evidence that endocardial integrity was maintained and endocardial cell loss was not responsible for the reduction of TM expression. The present study demonstrates that TM protein expression on the endocardial surface is reduced by greater than 80% in heart failure patients. Mechanical ventricular assistance restores endocardial TM levels up to 77% of control LV. The observable restoration of endocardial TM by mechanical ventricular assistance may rescue the loss of thromboresistance that is characteristic in heart failure.