Apoptotic myocardial degeneration in thrombotic thrombocytopenic purpura

The objective of this study was to determine whether the known myocardial degeneration in TTP is due to apoptosis. In TTP the heart is often involved, including the cardiac conduction system. Despite many platelet occlusions of small coronary arteries, there is little myocardial necrosis. Why the intermittent clinical episodes begin or end is unknown. Six hearts of patients dying with TTP were examined with routine and immunohistochemical stains. In addition to ventricular and atrial myocardium we examined the cardiac conduction system and coronary chemoreceptor. Numerous small coronary arteries were occluded with platelet thrombi in all these sites, including especially the sinus node, AV node and His bundle. The myocardial degeneration we found was conspicuously devoid of inflammation and the myocytes were relatively intact. These characteristics combined with TUNEL-positivity in the degenerating cells are typical of apoptosis. The focal degeneration in TTP is primarily apoptotic. Because circulating serotonin is carried by platelets and is released during aggregation, and because serotonin can cause a powerful cardiogenic hypertensive chemoreflex, we suggest that such a response may dislodge early platelet aggregations. Lessons from TTP may have special relevance for better understanding of myocardial reperfusion problems associated with angioplasty, thrombolysis and ischemic preconditioning.