Natural History of Nonobstructive Hypertrophic Cardiomyopathy
What is the natural history of left ventricular outflow tract (LVOT) gradients in nonobstructive hypertrophic cardiomyopathy (HCM)?
The authors prospectively studied 573 consecutive patients with HCM (mean age 44 ± 17 years, 66% male) with mild New York Heart Association (NYHA) class I/II symptoms at study entry. These included 249 patients in whom LVOT obstruction was absent both at rest and following physiological exercise (<30 mm Hg). They then retrospectively assembled clinical data. They utilized a multivariate Cox proportional hazards model to identify independent predictors. The Kaplan-Meier method was used for survival analysis.
The median period of follow-up was 6.5 years. During the study period, 90% of the cohort (n = 225) remained NYHA class I/II, whereas 10% (n = 24) developed progressive heart failure NYHA class III/IV. When they compared the nonobstructive (n = 249) with the obstructive HCM patients (n = 324), they found they were less likely to progress to NYHA class III/IV (1.6% per year vs. 7.4% per year for rest obstruction, vs. 3.2% per year for provocable obstruction; p < 0.001). Among the 24 patients with nonobstructive HCM who developed class III/IV heart failure, 12 declined or did not qualify and 2.8% (n = 7) underwent cardiac transplant when compared to none of the obstructive patients. The 24 patients who progressed when compared to other nonobstructive patients were more likely to be symptomatic at baseline in class II (62% vs. 24%; p < 0.0010); also to have larger left atria (46 ± 8 mm vs. 39 ± 7 mm; p < 0.001), more frequent history of atrial fibrillation (58% vs. 15%; p < 0.001), lower ejection fraction (60 ± 8 vs. 63 ± 6, p = 0.04), and more extensive late gadolinium enhancement (15 ± 14% vs. 6 ± 9%; p = 0.008). Multivariate analysis predicted that left atrial size and class II symptoms at study were independent predictors for progression to class III/IV heart failure. Mortality related to HCM was low in nonobstructive patients (n = 8; 0.5% per year) with 5- and 10-year survival rates of 99% and 97%, respectively, and this was not different from expected all-cause mortality in the age- and gender-matched US population (p = 0.15).
The authors concluded that nonobstructive HCM is a relatively benign disease and only a small minority of patients progress to requiring cardiac transplantation.
This is an important study because the findings indicate that nonobstructive HCM (which comprises a third of all HCM patients) is a relatively benign condition with a low risk (0.5% per year) of developing complications such as sudden death, progressive heart failure, or embolic stroke. These data should be reassuring for patients with nonobstructive HCM.
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