Abstract 4140424: Early Insights on Mavacamten Usage in Canada: A Retrospective Cohort Study of the Patient Support Program

Introduction: Mavacamten is a first-in-class cardiac myosin inhibitor initially approved in the US for treating obstructive hypertrophic cardiomyopathy (oHCM) under the FDA-mandated Risk Evaluation Mitigation Strategy (REMS). Subsequently, mavacamten was approved in Canada with less restrictions. A patient support program (PSP) was implemented, offering a unique opportunity to generate data on mavacamten utilization in the Canadian population. Aims: The objective of the study was to obtain real-world insights into the demographic and clinical characteristics, including dosing and treatment duration of patients treated with mavacamten for oHCM in Canada. Methods: This was an observational retrospective study of 683 adult patients with symptomatic oHCM enrolled in the Canadian mavacamten PSP between January 4, 2023 to April 12, 2024. Baseline demographic and clinical data were collected for age, gender, NYHA class, vLVOT gradient, LVEF and change in mavacamten dose. Results: The baseline clinical characteristics of the 683 patients are summarized in Table 1. Patients were distributed across several provinces with a median age of 65 years and a similar distribution between the male and female populations. The majority (N=458: 67.1%) were classified as NYHA class II. Nearly all patients were initiated at 5 mg of mavacamten as per the Canadian product monograph. Most (63.7%) of patients were on β-blockers alone (Table 1). The median follow-up time was 27.4 weeks (range 1.6-70.1). Notably, at the time of data cut off, 13.2% of patients were receiving mavacamten alone compared to 10.5% at initiation. The median treatment duration was 24.6 weeks, censored at data cut-off, with a discontinuation rate of 7.9%, primarily due to adverse events (2.5%) and lack of efficacy (0.9%). Conclusions: Mavacamten has been widely adopted across Canada with low discontinuation rates indicating good tolerability. The current risk management strategies in Canada are sufficient and obviate the need for a stricter approach. These early results provide the largest dataset on mavacamten utilization in the Canadian HCM population, adding to the accruing evidence of its safe and effective use in the real world.