The assumption that a mild presentation of hypertrophic cardiomyopathy means a benign trajectory is overdue for revision. For the estimated one-in-500 adults carrying this genetic cardiac condition, a classification of "phenotypically mild" has often provided false reassurance — this large registry study reframes that complacency with hard outcome data.
Drawing on the Sarcomeric Human Cardiomyopathy Registry (SHaRe), investigators prospectively tracked 2,500 individuals meeting strict criteria for phenotypically mild hypertrophic cardiomyopathy (HCM): disease duration under ten years or age 30 or younger, no prior major adverse cardiovascular events (MACE), NYHA functional class I status, and a left ventricular maximal wall thickness below 25 mm. Despite this seemingly favorable profile, 534 participants — roughly one in five — developed MACE over a mean follow-up of seven years. Atrial fibrillation accounted for the largest share, with 289 cases, while malignant ventricular arrhythmia, heart failure progression, stroke, and all-cause mortality also emerged. Cox regression modeling identified discrete predictors of incident MACE, and latent class mixed modeling revealed distinct left ventricular remodeling trajectories and risk clusters within this ostensibly uniform population.
What makes this finding particularly consequential is the timing: the field of HCM is actively debating when to deploy emerging disease-modifying therapies — cardiac myosin inhibitors like mavacamten — before overt symptoms develop. A 21% MACE incidence in the mildest disease stratum suggests the window for early intervention may be narrower than previously appreciated. The registry's trajectory modeling is especially valuable, as it implies that remodeling patterns observable before symptoms develop could stratify who needs accelerated monitoring. Key limitations include the observational registry design, which precludes causal inference, and potential selection bias toward academic HCM centers. Still, the 2,500-participant cohort is among the largest prospective mild-HCM datasets assembled. This is a confirmatory but clinically urgent finding: apparent stability in HCM deserves active, data-driven surveillance rather than watchful waiting.