This study aimed to determine whether clinicians are encountering a phenotype of hypertrophic cardiomyopathy that is evolving from the disease recognized several years ago.

A total of 3161 consecutive patients with established hypertrophic cardiomyopathy were encountered (2003-2020) and studied clinically with imaging.

Patients were identified as progressively older now (average 56 ± 15 years) compared with previously (44 ± 17 years; P < .001), and with an increasing frequency of outflow obstruction (from 46% to 61% of patients; P < .001), albeit without more advanced heart failure symptoms. Notably, maximum left ventricular wall thickness (usually ventricular septum) decreased progressively over the same period (20.4 ± 5.7 to 17.5 ± 3.4 mm).

These novel observations are counter-intuitive to practitioners (expecting hypertrophic cardiomyopathy to be associated with particularly substantial hypertrophy), and potentially impact disease recognition, while also highlighting emergence of symptomatic obstructive patients with mild septal thickness < 15 mm, requiring modification of the traditional myectomy operation. While a primary change in the phenotypic expression of hypertrophic cardiomyopathy cannot be excluded by our data, these observations most likely reflect evolving referral practice patterns including greater diagnostic suspicion for the disease in the community particularly at advanced ages, and/or with less substantial left ventricular hypertrophy.