The End of the Beta-Blocker Era in oHCM?
For more than 60 years, the pharmacological management of symptomatic obstructive hypertrophic cardiomyopathy (oHCM) has relied heavily on beta-blockers as first-line therapy. Despite this long-standing clinical tradition, the evidence supporting beta-blockers for improving exercise capacity or altering the disease course in oHCM has been surprisingly limited. The emergence of cardiac myosin inhibitors has fundamentally shifted the therapeutic paradigm, moving away from non-specific negative inotropy and toward targeted molecular intervention. The MAPLE-HCM trial, a Phase 3 head-to-head comparison, marks a pivotal moment in this evolution, positioning aficamten not just as an alternative, but as a potentially superior primary treatment option over metoprolol.
The MAPLE-HCM Study Design and Multidomain Methodology
The MAPLE-HCM trial was a multicenter, randomized, double-blind study that enrolled 175 patients with symptomatic oHCM. Participants were required to have a left ventricular outflow tract gradient (LVOT-G) of at least 30 mm Hg at rest or 50 mm Hg during the Valsalva maneuver. Patients were randomized to receive either aficamten (n = 88) or metoprolol succinate (n = 87). Dose titration was performed meticulously over several weeks, guided by vital signs and echocardiographic monitoring of the left ventricular ejection fraction (LVEF) and LVOT gradients.
What sets this specific analysis apart is its multidomain, patient-level approach. Recognizing that oHCM is a complex disease affecting hemodynamics, functional capacity, biomarkers, and quality of life, the investigators evaluated five key clinical response domains:
1. Hemodynamic relief: Achieving an LVOT-G <30 mm Hg at rest and <50 mm Hg with Valsalva.
2. Functional/Quality of Life improvement: At least one NYHA class improvement or a 10-point increase in the Kansas City Cardiomyopathy Questionnaire-Clinical Summary Score (KCCQ-CSS).
3. Biochemical markers: A reduction of 50% or more in N-terminal pro-B-type natriuretic peptide (NT-proBNP).
4. Exercise capacity: An increase in peak oxygen consumption (pVO2) of 1.0 mL/kg/min or more.
5. Cardiac remodeling: A reduction of 10% or more in the left atrial volume index (LAVI).
Patients were categorized based on how many of these efficacy outcomes they achieved: nonresponders (0), limited (1-2), positive (3-4), or complete (all 5).
Results: Unprecedented Clinical Response
The baseline characteristics of the cohort reflected a typical symptomatic oHCM population, with a mean age of 58 years and a significant portion (30%) in NYHA functional class III. After 24 weeks of treatment, the results revealed a stark contrast between the two therapies. Aficamten treatment was associated with significantly greater benefits across every efficacy outcome measure evaluated.
The most compelling finding was the proportion of patients achieving a high-level clinical response. In the aficamten group, 78% of patients were classified as either positive or complete responders, compared to a mere 3% in the metoprolol group (P < 0.001). This massive delta underscores the limitations of beta-blockade in addressing the multifaceted burden of oHCM. Furthermore, the number needed to treat (NNT) for aficamten relative to metoprolol was remarkably low, ranging from 1.5 to 5.0 across the various domains. In clinical practice, an NNT of 1.5 for a primary endpoint is almost unheard of, suggesting that for nearly every patient switched from or started on aficamten instead of metoprolol, a tangible clinical benefit is realized.
Hemodynamic and Functional Superiority
Aficamten’s ability to relieve the LVOT gradient was superior and more rapid than that of metoprolol. By reducing the number of active actin-myosin cross-bridges, aficamten directly addresses the hypercontractility that drives the obstruction. This translated into significant improvements in pVO2, a critical measure of aerobic exercise capacity that strongly correlates with long-term prognosis in heart failure. While beta-blockers can sometimes limit peak heart rate and thus blunt pVO2, aficamten allowed for functional improvement without the negative chronotropic limitations of metoprolol.
From a patient-centric perspective, the KCCQ-CSS data demonstrated that those on aficamten felt significantly better. The rapid reduction in NT-proBNP—a marker of myocardial wall stress—further supports the hypothesis that aficamten provides systemic relief to the heart, potentially slowing the long-term adverse remodeling associated with chronic obstruction.
Safety and Mechanistic Insights
Safety is a paramount concern with cardiac myosin inhibitors, as excessive inhibition can lead to a reduction in LVEF below the normal range. In MAPLE-HCM, dose titration based on echocardiography proved to be an effective strategy for maintaining safety while maximizing efficacy. The incidence of treatment-emergent adverse events was comparable between the two groups, and the protocol-defined titration ensured that hemodynamic relief was achieved without compromising systemic perfusion.
Mechanistically, metoprolol acts as a blunt instrument, slowing the heart and potentially lengthening diastole to improve filling, but it does nothing to correct the underlying sarcomeric overactivity. Aficamten, as a next-generation myosin inhibitor, offers a more refined approach with a shorter half-life and faster steady-state achievement than its predecessors, allowing for more nimble dose adjustments and a quicker onset of action.
Expert Commentary and Clinical Implications
The findings from MAPLE-HCM challenge the current guidelines that mandate a trial of beta-blockers before considering more advanced therapies. If a drug like aficamten can provide a “positive or complete” response in nearly 80% of patients while the current gold standard does so in only 3%, the ethical and clinical rationale for delaying myosin inhibitor therapy becomes increasingly difficult to maintain.
However, some experts note that cost and access remain significant hurdles. Beta-blockers are inexpensive and widely available, whereas novel myosin inhibitors represent a significant financial investment for healthcare systems. Nevertheless, the multidomain analysis provided by Wang et al. suggests that the comprehensive benefit of aficamten—ranging from symptomatic relief to improved exercise capacity and favorable remodeling—may offset these costs by reducing the need for septal reduction therapies (alcohol septal ablation or myectomy) and decreasing heart failure-related hospitalizations.
Conclusion
The MAPLE-HCM trial provides robust, multidomain evidence that aficamten monotherapy is superior to metoprolol in patients with symptomatic obstructive hypertrophic cardiomyopathy. By achieving rapid and comprehensive improvements in hemodynamics, functional capacity, and patient-reported outcomes, aficamten establishes itself as a formidable candidate for first-line therapy. As the medical community moves toward a more personalized and pathophysiology-driven approach to HCM, aficamten represents a significant leap forward in our ability to reduce the heavy disease burden carried by these patients.
Funding and Clinical Trial Information
The MAPLE-HCM trial was funded by Cytokinetics, Inc. ClinicalTrials.gov Identifier: NCT05767346.
References
1. Wang A, Garcia-Pavia P, Masri A, et al. Aficamten in Obstructive Hypertrophic Cardiomyopathy: A Multidomain, Patient-Level Analysis of the MAPLE-HCM Trial. J Am Coll Cardiol. 2025 Nov 18. doi: 10.1016/j.jacc.2025.10.057.
2. Maron MS, Hellawell JL, Lucove JC, et al. Improvement in Exercise Capacity and Patient-Reported Outcomes With Aficamten in Obstructive Hypertrophic Cardiomyopathy. J Am Coll Cardiol. 2024.
3. Semsarian C, Ingles J, Maron MS, et al. New Era of Management for Hypertrophic Cardiomyopathy. J Am Coll Cardiol. 2023.
