Mavacamten in Obstructive Hypertrophic Cardiomyopathy-A First Australian Experience

Mavacamten, a first-in-class, cardiac-specific myosin inhibitor, has recently been approved in Australia as second-line therapy in patients with obstructive hypertrophic cardiomyopathy (oHCM) and New York Heart Association (NYHA) class II-III symptoms. Mavacamten reduces left ventricular (LV) outflow tract (LVOT) gradients and improves angina and heart failure symptoms. Several international studies have demonstrated the profound clinical benefit of mavacamten in patients with oHCM. However, there has been no reported "real-world" Australian data. This study aimed to assess the impact and safety of mavacamten in an Australian cohort with symptomatic oHCM.

In this single-centre observational study, we assessed baseline characteristics, at rest and Valsalva LVOT gradients, LV ejection fraction (LVEF), LV global longitudinal function, and NYHA class in patients with symptomatic oHCM treated with mavacamten over 24 weeks.

A total of 23 patients received mavacamten. Baseline characteristics are the following: mean age was 63±11 years, 52% were male, and 21 of 23 (91%) were on beta blockers. The mean gradients across the LVOT were 56±28 mmHg at rest and 92±29 mmHg with Valsalva manoeuvre. The mean LVEF was 66%, and 52% of patients reported NYHA class III symptoms at entry. At 24 weeks, mean at rest and Valsalva LVOT gradients showed statistically significant reduction (at rest, 16±13 mmHg; Valsalva, 37±36 mmHg; both p<0.001). Although statistically significant, the LVEF drop does not appear clinically significant (66% to 62%; p=0.02). LV global longitudinal function remained largely static across 24 weeks (-15.3% to -15.6%; p=0.6). A total of 70% of patients experienced at least one NYHA class improvement. Patient adherence was high, with 99% of all scheduled appointments attended. A total of 39 treatment-emergent adverse events occurred, of which 38% were cardiac-related. Over 24 weeks, three of 23 (13%) patients permanently discontinued mavacamten.

Our results provide novel real-world Australian data on the use of mavacamten in patients with oHCM. Approximately 70% of patients experienced significant clinical and echocardiographic improvement in first 6 months after drug initiation, with a tolerable safety profile.