Long-Term Efficacy and Safety of Mavacamten in Chinese Patients With Obstructive Hypertrophic Cardiomyopathy: Week 78 Results From the EXPLORER-CN Study.
Tian Z, Li X, et al. • Journal of the American Heart Association • 2026
78-week mavacamten treatment appeared well-tolerated and was associated with numerical improvements from baseline in echocardiographic parameters, New York Heart Association class, patient-reported health status, and cardiac biomarkers in Chinese patients with obstructive hypertrophic cardiomyopathy.
Key Findings
Results
Mavacamten-mavacamten group maintained substantial reductions in Valsalva left ventricular outflow tract (LVOT) peak gradient through week 78.
Mean change from baseline in Valsalva LVOT peak gradient was -73.0 mm Hg (95% CI, -86.4 to -59.5) at week 78
Mean change from baseline in resting LVOT peak gradient was -56.3 mm Hg (95% CI, -67.1 to -45.5) at week 78
These improvements were described as 'maintained through week 78' in the mavacamten-mavacamten group (n=54)
Analyses were descriptive with no between-group hypothesis testing performed
Results
Patients who switched from placebo to mavacamten at week 30 showed numerical improvements in echocardiographic and clinical parameters from week 30 to week 78.
The placebo-mavacamten group (n=25) started mavacamten at an initial dose of 2.5 mg once daily at week 30
Numerical improvements were noted from week 30 to week 78 in LVOT peak gradients, New York Heart Association class, Kansas City Cardiomyopathy Questionnaire Clinical Summary Score, and cardiac biomarkers
The pattern of improvement after switching from placebo mirrored the trajectory seen in the original mavacamten group
Results were descriptive and no formal statistical comparisons between groups were performed
Results
Long-term mavacamten treatment was associated with numerical improvements in New York Heart Association functional class through week 78.
NYHA functional class improvement was observed in both the mavacamten-mavacamten and placebo-mavacamten groups
Improvements were maintained through week 78 in the mavacamten-mavacamten group
The placebo-mavacamten group showed improvements from week 30 onward after initiating mavacamten
Analyses were descriptive in nature
Results
Patient-reported health status, as measured by the 23-item Kansas City Cardiomyopathy Questionnaire Clinical Summary Score (KCCQ-23 CSS), showed numerical improvements through week 78.
KCCQ-23 CSS improvements were observed in the mavacamten-mavacamten group and maintained through week 78
The placebo-mavacamten group showed KCCQ-23 CSS improvements after initiating mavacamten at week 30
Results represent patient-reported outcomes alongside objective echocardiographic and biomarker measures
No formal between-group statistical testing was conducted
Results
Cardiac biomarkers showed numerical improvements with mavacamten through week 78 in both treatment groups.
Cardiac biomarker improvements were observed in the mavacamten-mavacamten group and maintained through week 78
The placebo-mavacamten group showed improvements in cardiac biomarkers after switching to mavacamten at week 30
Specific biomarker types assessed were not enumerated in the abstract but are standard measures used in hypertrophic cardiomyopathy trials (e.g., NT-proBNP, troponin)
Results were descriptive
Results
Left ventricular ejection fraction (LVEF) below 50% was rare during 78 weeks of mavacamten treatment, indicating an acceptable long-term safety profile.
LVEF <50% was described as 'rare' in this long-term extension cohort
Long-term mavacamten treatment 'appeared well tolerated' over the 48-week extension period (total 78 weeks including the original 30-week double-blind period)
79 patients entered the long-term extension period (mavacamten-mavacamten, n=54; placebo-mavacamten, n=25)
Only patients who completed the 30-week double-blind period with no active safety concerns were eligible to enter the extension
Methods
The EXPLORER-CN long-term extension enrolled 79 Chinese patients with obstructive hypertrophic cardiomyopathy who had completed the 30-week double-blind phase.
Mean age of participants was 51.6 years; 27.8% were women
54 patients were in the mavacamten-mavacamten group and 25 were in the placebo-mavacamten group
The long-term extension consisted of 48 weeks of open-label mavacamten treatment following the 30-week double-blind, placebo-controlled period
Patients previously on placebo started mavacamten at 2.5 mg once daily; those previously on mavacamten continued at their week 30 dose
The study was registered at ClinicalTrials.gov (NCT05174416)
What This Means
This research examined the long-term effects of mavacamten, a medication for a heart condition called obstructive hypertrophic cardiomyopathy (HCM), in Chinese patients over 78 weeks total. HCM causes the heart muscle to thicken abnormally, which can obstruct blood flow and cause symptoms like breathlessness and reduced exercise capacity. The study followed 79 patients who had already completed a 30-week controlled trial: one group continued mavacamten for an additional 48 weeks, while another group switched from a placebo to mavacamten at the 30-week mark.
This research suggests that the benefits of mavacamten seen in the initial 30-week trial were maintained over the longer 78-week period. Patients who took mavacamten throughout showed continued reductions in the pressure gradient within the heart (a key measure of obstruction), as well as improvements in heart function measures, symptom classifications, patient-reported quality of life, and blood markers of heart stress. Patients who switched from placebo to mavacamten at week 30 began showing similar improvements after starting the drug. Importantly, a serious side effect — the heart's pumping function dropping too low (ejection fraction below 50%) — was uncommon, suggesting the drug was generally safe over this longer period.
These findings are notable because they represent the first long-term data on mavacamten specifically in Chinese patients with HCM, a population that may differ from those studied in earlier global trials. This research suggests that the drug's benefits persist and remain tolerable over nearly 18 months of treatment, which is relevant for patients with a chronic condition like HCM who would need long-term therapy. However, the study was exploratory and descriptive — without a control group comparison at the extension stage — so conclusions about efficacy should be interpreted with caution.
Tian Z, Li X, Li L, Zhang Q, Wang J, Shi Y, et al.. (2026). Long-Term Efficacy and Safety of Mavacamten in Chinese Patients With Obstructive Hypertrophic Cardiomyopathy: Week 78 Results From the EXPLORER-CN Study.. Journal of the American Heart Association. https://doi.org/10.1161/JAHA.125.046251