Circadian variability in the occurrence of sudden cardiac death in patients with hypertrophic cardiomyopathy

Cardiovascular Research Division, Minneapolis Heart Institute Foundation, Minnesota 55407.

OBJECTIVES. The present study examined whether sudden death in patients with hypertrophic cardiomyopathy occurred with a particular pattern of frequency throughout the day. BACKGROUND. Previous investigators have shown a circadian distribution in the occurrence of sudden death and other cardiovascular events in patients with atherosclerotic coronary artery disease. Sudden death is also an important feature of the natural history of patients with hypertrophic cardiomyopathy. METHODS. The study group comprised 94 patients with a time of death (or cardiac arrest) that could be ascertained accurately to the nearest hour. This hourly distribution was analyzed by harmonic regression. RESULTS. Sudden death did not occur uniformly or randomly throughout the day. Rather, it was distributed in a bimodal pattern that conformed to a two-harmonic regression model. A disproportionate number of sudden deaths (43 [46%] of 94) occurred in the first peak in midmorning between 7 AM and 1 PM. The second peak of sudden death was less distinct but was in the early evening, between 8 PM and 10 PM. This periodicity in occurrence of sudden cardiac death was not evident for the days of the week or months of the year and, furthermore, did not appear to be influenced by other clinical variables, such as age, gender, severity of symptoms, subaortic gradient or left ventricular wall thickness. Sudden death occurred most commonly during periods of severe exertion (37 [39%] of 94). CONCLUSIONS. Sudden death in hypertrophic cardiomyopathy demonstrates a bimodal pattern of circadian variability over the 24-h day, with a prominent midmorning peak similar to that described in patients with coronary artery disease, and a less striking early-evening peak of occurrence. These findings suggest that temporally related physiologic changes, possibly in the electrical vulnerability of the myocardial substrate, may play a role in the sudden death of patients with hypertrophic cardiomyopathy.

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