Sickle cells and sudden death: morphologic abnormalities of the cardiac conduction system.

Sudden unexpected death has become increasingly recognized as an important clinical feature of both homozygous and heterozygous sickling syndromes, but the exact nature of its cause has remained unexplained. We have conducted special postmortem examinations of the cardiac conduction system and a coronary chemoreceptor from the hearts of two black males who had sickled erythrocytes. There were abundant foci of old and recent degeneration in the sinus node, atrioventricular node, and His bundle, as well as the coronary chemoreceptor. Many capillaries and small arteries were packed with sickled erythrocytes, among which small groups of aggregated platelets were also present. Focal fibromuscular dysplasia caused moderate to severe narrowing of many small coronary arteries, including those supplying the conduction system and chemoreceptor. These abnormalities are suggestive of electrical instability of the heart as at least one component of the lethal terminal events in some individuals with sickled erythrocytes. Both the foci of fibrosis and the focal fibromuscular dysplasia of small coronary arteries cannot be simply terminal or recent events but more likely take months or years in developing. For individuals with sickled erythrocytes, as in other examples of sudden death, there is a major element of chance concurrence of numerous otherwise independently less significant factors, but lethal cardiac electrical instability may be the final common pathway.