Changes in standard of care (SOC) medication during long-term mavacamten treatment for obstructive hypertrophic cardiomyopathy (HCM): results from the EXPLORER cohort of MAVA-Long-Term Extension (LTE)

Abstract Introduction Mavacamten is efficacious and well tolerated in patients with obstructive HCM in the ongoing MAVA-LTE study (NCT03723655) as shown in previous interim analyses. Here, we present exploratory data from the EXPLORER cohort of MAVA-LTE investigating the effect of changes in SOC treatment on the efficacy and safety of mavacamten. Methods Patients who completed EXPLORER-HCM (NCT03470545) could enroll in MAVA-LTE and comprised the EXPLORER cohort. All patients in the EXPLORER cohort received mavacamten. Patients could receive beta blockers or nondihydropyridine calcium channel blockers (verapamil/diltiazem) as SOC treatment. After 24 weeks on study, SOC treatment could be adjusted. A cumulative interim analysis (data cut-off: May 31, 2022) was performed on patients who: received no SOC, discontinued SOC, had any reduction in SOC and had ≥50% reduction in SOC from baseline to data cut-off. Results In total, 231 patients (mean age, 60 years; 39% female) comprised the EXPLORER-LTE cohort (median time on study: 101 weeks at data cut-off). At baseline, 176 patients (76.2%) received beta blockers and 38 (16.5%) received nondihydropyridine calcium channel blockers. At data cut-off, 12 (5.2%) patients had received no SOC treatment from baseline, 11 (4.8%) patients had discontinued SOC, 27 (11.7%) patients had any dose reduction in SOC, 18 (7.8%) patients had a ≥50% reduction in SOC and 14 (6.1%) patients had an increase in SOC. In the no SOC subgroup, mavacamten treatment was associated with improvements from baseline to last visit in resting and Valsalva left ventricular outflow tract (LVOT) gradients, left atrial volume index (LAVI), and N-terminal pro B-type natriuretic peptide (NT-proBNP) levels (Table 1). Improvements in these parameters were also observed in the SOC discontinuation and SOC dose reduction subgroups (Table 1). In the SOC discontinuation subgroup, improvements in resting and Valsalva LVOT gradients, LAVI, and NT-proBNP levels from baseline were maintained after SOC discontinuation (Table 1). SOC medications were discontinued or reduced over a mean (range) period of 63 (9–96) and 62 (3–133) weeks, respectively. At data cut-off, left ventricular ejection fraction remained within the normal range for all patients regardless of the SOC subgroup. Patients who reduced SOC medication had small increases in heart rate (within normal range) from baseline to last visit (Table 2). Overall, blood pressure remained stable across subgroups thr