Abraham, Theodore P.

Background: MARVEL-HCM is a US multicenter study assessing the safety and effectiveness of mavacamten in real-world academic and community practices. Mavacamten is a first-in-class cardiac myosin inhibitor (CMI) and the only CMI currently approved in over 50 countries for use in patients with symptomatic obstructive hypertrophic cardiomyopathy (oHCM). Modest evidence exists describing the effectiveness and safety of mavacamten monotherapy. Aims: To describe the real-world outcomes of patients using mavacamten as monotherapy for oHCM. Methods: Patient-level data from medical records at 5 sites were analyzed to describe mavacamten monotherapy, defined as monotherapy at baseline or after background HCM therapy (beta-blockers [BB], calcium channel blockers [CCB], disopyramide) discontinuation within 12 weeks(wks) of mavacamten initiation and without reinitiation, up to 60 wks. A minimum of 12 wks follow-up was required for inclusion. Patient characteristics, echocardiographic data, and safety are reported at baseline and follow-up visits. Results: The monotherapy cohort comprised 13.4% (32/239) of patients: 24 were on mavacamten monotherapy at initiation, and 8 discontinued background therapy. Baseline characteristics included: NYHA Class II (46.9%) and III (53.1%), female (66%), hypertension (50%), and atrial fibrillation (AF) (18%) (Table 1). Median follow-up and duration of mavacamten monotherapy were 48 wks (range 12-60 wks) and 57 wks (range 14-60 wks), respectively. Resting left ventricular outflow tract gradient (LVOTg) was ≤ 30 mmHg in 93%, 91% and 100% of patients at Wk 24, 36, and 60. Valsalva LVOTg was ≤ 30 mmHg in 61%, 77% and 86% of patients at Wk 24, 36, and 60 (Fig 1). No patients were in NYHA Class III at wk 60, and ~50% of patients were NYHA Class I by wk 48 (Fig 2). Mean reduction in LVEF was 4.8% over 60 wks. One patient had LVEF < 50% at Wk 20, resulting in a dose reduction (10 to 7.5 mg). Safety events included 3 hospitalizations due to AF ablation (n=1), viral gastrointestinal illness (n=1) and heart failure (n=1). Demographic, clinical characteristics, and outcomes were similar across the mavacamten monotherapy cohort, mavacamten in combination with background HCM therapy (n=207), and the overall cohort of MARVEL-HCM (N=239). Conclusions: Mavacamten monotherapy was effective, safe, and consistent with the overall MARVEL cohort, as well as previously reported monotherapy cohorts from pivotal, long-term, and real-world evidence.

Background: Mavacamten was approved by the US Food and Drug Administration (FDA) in April 2022 for the treatment of adults with New York Heart Association (NYHA) class II-III symptomatic obstructive hypertrophic cardiomyopathy (HCM). Few studies have reported on the long-term real-world effectiveness and safety of mavacamten. We evaluated clinical outcomes in patients on mavacamten in multiple health centers across the United States. Research Questions: This study assessed the real-world effectiveness and safety of mavacamten in patients with symptomatic obstructive HCM. Methods: In this multi-center observational study, we evaluated patient characteristics at baseline, NYHA class, left ventricular outflow tract gradients (LVOTg) at rest and Valsalva, and left ventricular ejection fraction (LVEF) in patients with symptomatic obstructive HCM treated with mavacamten for up to 72 weeks. Results: Mavacamten was initiated in 172 patients across 4 US centers (UCSF, Mayo Arizona, Stanford, and Atlantic Health System/Morristown Medical Center). Baseline characteristics included: 56% female, mean age 64 (standard deviation ±13) years, 47% NYHA class III, mean resting LVOTg of 47 mmHg and mean Valsalva LVOTg of 89 mmHg, and 23% non-White. Comorbidities included hypertension (56%) and atrial fibrillation (25%) at baseline (Table). Patients experienced a notable early response to mavacamten in resting and Valsalva gradients by week 4, which was sustained through week 72 (Figure A). No patients were NYHA class III at week 72, compared to 47% at baseline (Figure B). Mean LVEF did not change substantially between baseline and week 72. No patients experienced an LVEF of <40% and 2% experienced an LVEF of <50%. Conclusions: This is the largest observational study to date demonstrating the effectiveness and safety of mavacamten with substantial sustained reductions in resting and Valsalva LVOTg, and progressive improvements in NYHA class without considerable changes in mean LVEF up to 72 weeks.

Background— Onset of myocardial relaxation is highly energy dependent. Perfusion and therefore energy substrate delivery are predominantly reduced in the subendocardial myocardium in the early stages of progressive ischemia. We hypothesized that delayed onset of subendocardial diastolic thinning will functionally identify regionally hypoperfused resting myocardium. Methods and Results— Progressive left anterior descending coronary artery stenosis was induced by an ameroid occluder and maintained for 1 or 2 weeks (end point) in 12 dogs. M-mode tissue Doppler images of the anterior apical and middle segments (testing region) and middle inferior segment (control region) were acquired selectively in the subendocardium and subepicardium. The time to the onset of thinning was measured with the use of tissue Doppler velocity (TOTv) and a thickness function (TOTt). At the end point in the testing region, myocardial flow was significantly lower in the subendocardial layer ( P <0.05) in all animals, whereas viability staining showed preserved transmural viability in 10 dogs and thin subendocardial necrosis in 2 dogs. Both TOTv and TOTt were significantly ( P <0.01) prolonged in the testing region. The mean difference between subendocardial and subepicardial TOTv values versus that in the control region identified the ischemic region, even when only dogs with hypoperfused but transmurally viable myocardium were considered ( P <0.05). Systolic and diastolic myocardial velocities did not identify subendocardial hypoperfusion. Conclusions— In resting myocardium subtended to progressive coronary stenosis, a delayed onset of subendocardial thinning suggests an early stage of hypoperfusion, before the development of local wall motion abnormalities.