Background: Idiopathic dilated cardiomyopathy is often familial, and apparently healthy relatives may have latent, early, or undiagnosed established disease. Objective: To determine the prevalence and natural history of asymptomatic cardiac abnormalities among sampled relatives of unselected patients referred for management of dilated cardiomyopathy. Design: Prospective cohort study. Patients: 767 asymptomatic relatives of 189 consecutive unselected patients with dilated cardiomyopathy. Measurements: Clinical evaluation, including history, physical examination, electrocardiography, and echocardiography, was performed. Participants were classified in accordance with published echocardiographic criteria. Sampled relatives who did not have evidence of dilated cardiomyopathy at the initial evaluation were followed for a median of 57 months(range, 1 to 133 months). Results: Of the 767 patients evaluated, 592(77.2%) were assessed as healthy, 35(4.6%[95%CI, 3.7%to 7.6%]) had dilated cardiomyopathy, 119(15.5%[CI, 12.5%to 18.8%]) had left ventricular enlargement without systolic dysfunction, and 21(2.7%[CI, 1.9%to 4.9%]) had depressed fractional shortening without ventricular dilatation. At follow-up, progression to dilated cardiomyopathy occurred in 13(10%) relatives with left ventricular enlargement or depressed fractional shortening versus 3(1.3%) healthy relatives. In a multivariate model, only left ventricular enlargement or depressed fractional shortening independently predicted progression to dilated cardiomyopathy(hazard ratio, 10.0[CI, 2.8 to 35.5]; P< 0.001). Limitations: Because relatives had to be willing to participate and be available geographically, selection bias may have occurred. Conclusion: Treatable asymptomatic dilated cardiomyopathy was identified in 4.6%of asymptomatic relatives. In addition, left ventricular enlargement and depressed fractional shortening were common in asymptomatic relatives of patients with dilated cardiomyopathy and were associated with a statistically significant medium-term risk for disease progression. Evaluation of relatives of patients with cardiomyopathy is recommended.
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