Objectives: The purpose of this study was to characterize the prognosis of minimally symptomatic patients with obstructive hypertrophic cardiomyopathy (HCM).

Background: Recent data have suggested that obstruction may be present in the majority of HCM patients, irrespective of cardiac symptoms. The prognosis of minimally symptomatic obstructive HCM remains poorly defined.

Methods: We examined 544 consecutive adult patients (age 59 +/- 16 years; 55% men) with obstructive HCM documented by Doppler echocardiography who were free of severe cardiac symptoms, and we performed clinical follow-up (median 9.3 years).

Results: There was only a slight excess mortality of the cohort in comparison to the expected survival of a similar U.S. general population (10-year observed vs. expected survival, 69.3% vs. 71.9%; p = 0.04) and 46% of the deaths were attributable to noncardiac causes. However, there was a clear relation between increasing severity of the left ventricular outflow tract (LVOT) gradient and outcome. For patients with high resting gradients (Doppler peak velocity >4 m/s), survival was significantly impaired (53% at 10 years; p = 0.001 vs. expected), and death or severe symptoms occurred in 68% of these patients within 10 years after the initial evaluation. Conversely, there was no impairment of long-term survival for patients with less-severe resting obstruction. Independent predictors of mortality in the entire cohort were age, prior stroke, and LVOT gradient severity.

Conclusions: Patients with obstructive HCM and mild or no symptoms have only slight excess mortality. However, patients with markedly elevated resting LVOT gradients are at a high risk of heart failure and death. These findings may have important implications for therapy, including the timing of septal reduction therapy.