Results:

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).