Aficamten for Symptomatic Obstructive Hypertrophic Cardiomyopathy (SEQUOIA-HCM)

Authors, Journal, Affiliations, Type, DOI

• Authors: Martin S. Maron, Ahmad Masri, Michael E. Nassif, Roberto Barriales-Villa, et al., for the SEQUOIA-HCM Investigators
• Journal: New England Journal of Medicine
• Affiliations: Lahey Hospital and Medical Center, Burlington MA (lead); co-investigators from Brigham and Women's/Harvard, OHSU, Mayo, ESC-affiliated centres across Europe, Israel, China; sponsored by Cytokinetics
• Type: Phase 3, international, double-blind, randomized, placebo-controlled trial; 101 sites in 14 countries
• DOI: 10.1056/NEJMoa2401424 | ClinicalTrials.gov NCT05186818

Overview

SEQUOIA-HCM is the pivotal phase 3 RCT (N=282) that established aficamten's efficacy vs placebo in symptomatic obstructive HCM on a background of standard therapy (beta-blockers in 61%, disopyramide in 13%). Over 24 weeks, aficamten produced a placebo-corrected improvement in peak VO2 of +1.7 ml/kg/min (P<0.001), exceeding the pre-specified clinically important difference threshold of 1 ml/kg/min. All 10 prespecified secondary endpoints were significant, including NYHA class improvement (58.5% vs 24.3%), KCCQ-CSS (+7 points), Valsalva LVOTO gradient (−50 mmHg), NT-proBNP (80% reduction), and 78 fewer days of SRT eligibility. Safety was comparable to placebo; LVEF <50% occurred transiently in 3.5% with no heart failure exacerbations, consistent with the drug's shallow dose-response relationship.

Keywords

Hypertrophic cardiomyopathy, obstructive HCM, aficamten, cardiac myosin inhibitor, peak oxygen uptake, LVOTO gradient, NT-proBNP, exercise capacity, KCCQ, NYHA, septal reduction therapy

Key Takeaways

Background and Rationale

• HCM is the most common genetic heart disease; LVOTO — resulting from SAM of mitral valve contacting the ventricular septum — is a principal determinant of symptoms and complications
• Cardiac hypercontractility from excessive actin-myosin cross-bridge cycling is the primary mechanism promoting LVOTO; this was the mechanistic basis for aficamten development
• Established pharmacological therapies (beta-blockers, verapamil, disopyramide) have limited efficacy in reducing LVOTO gradient objectively and have not been shown to improve objective exercise capacity
• Mavacamten (first cardiac myosin inhibitor) demonstrated efficacy in EXPLORER-HCM (Lancet 2020); aficamten was designed with a shallower dose-response relationship and shorter half-life enabling more rapid dose adjustments vs mavacamten
• Prior phase 2 REDWOOD-HCM trial confirmed aficamten's hemodynamic efficacy; SEQUOIA-HCM was the phase 3 confirmatory trial

Trial Design

• Phase 3, international, double-blind, randomized, placebo-controlled trial; 101 sites in 14 countries; February 2022 – May 2023 enrollment
• N=282: 142 aficamten, 140 placebo (1:1 randomization)
• Eligibility: age 18–85; LV wall ≥15 mm; LVEF ≥60%; resting LVOTO ≥30 mmHg AND post-Valsalva LVOTO ≥50 mmHg; NYHA II–III; peak VO2 ≤90% predicted
• Background therapy: stable doses allowed >6 weeks before randomization (beta-blockers in 61.3%; disopyramide in 12.8%; AF capped ≤15%; cycle ergometer testing capped ≤50%)
• Aficamten starting dose 5 mg/day, up-titrated at weeks 2, 4, 6 to maximum 20 mg based on echo-guided algorithm (LVOTO gradient + LVEF); by week 8: 48.6% on 20 mg; 35.0% on 15 mg
• Treatment period 24 weeks followed by 4-week washout
• Core laboratory assessed all cardiopulmonary exercise testing and echocardiography

Primary Endpoint — Peak VO2 (Highly Significant)

• Aficamten: mean change from baseline +1.8 ml/kg/min (95% CI 1.2–2.3)
• Placebo: mean change 0.0 ml/kg/min (95% CI −0.5 to 0.5)
• Placebo-corrected difference: +1.7 ml/kg/min (95% CI 1.0–2.4; P<0.001)
• Exceeds the pre-specified minimal clinically important difference of 1.0 ml/kg/min
• Consistent across all prespecified subgroups, including NYHA class III, severe functional limitation (peak VO2 ≤18 ml/kg/min), background beta-blocker use or not, and presence/absence of pathogenic sarcomere variant

Secondary Endpoints — All 10 Statistically Significant

• Valsalva gradient reduction was rapid: mean difference −20 mmHg (95% CI −27.3 to −13.3) as early as week 2
• NT-proBNP (exploratory): geometric mean proportional change 0.20 aficamten vs 1.00 placebo — approximately 80% reduction; a clinically meaningful biomarker of HF severity

Pharmacokinetics and Dosing

• Shallow dose-response curve: small, incremental LVEF reductions as dose increased → wide therapeutic window for individualized titration
• Short enough half-life to allow dose adjustments every 2 weeks — faster titration than mavacamten
• Echo-guided dose adjustment at weeks 2, 4, 6 based on LVOTO gradient and LVEF thresholds

Safety

• Serious adverse events: 5.6% aficamten vs 9.3% placebo (comparable)
• Any adverse event: 73.9% aficamten vs 70.7% placebo
• LVEF <50% (core lab): 3.5% aficamten vs 0.7% placebo — transient; no patient with LVEF <50% had treatment interruption or HF exacerbation
• Per-protocol dose reduction (site echo): 4.9% aficamten
• Palpitations: 7.0% vs 2.9% (higher with aficamten)
• Hypertension: 7.7% vs 2.1% (higher with aficamten; mechanism unclear)
• Atrial fibrillation: 2.8% vs 2.9% (similar)
• 1 discontinuation from aficamten (paranoia); 2 from placebo (syncope; acute leukemia)
• After 4-week washout: LVOTO gradient, KCCQ-CSS, and LVEF returned toward baseline — confirming fully reversible pharmacodynamic mechanism

Comparison With Mavacamten (EXPLORER-HCM)

• In EXPLORER-HCM, treatment effect on peak VO2 was attenuated in patients receiving beta-blockers; in SEQUOIA-HCM, benefit was consistent regardless of beta-blocker use — a pharmacological distinction
• Both trials show the class mechanism works; aficamten's shallower dose-response may account for lower rates of LVEF reduction vs mavacamten (EXPLORER: higher LVEF <50% rates; PIONEER-HCM: 21.5%)
• No head-to-head trial between aficamten and mavacamten exists

Limitations of the Document

• Short 24-week treatment period — no data on long-term SCD prevention, HF hospitalisation, or all-cause mortality
• Limited ethnic diversity (European/North American/Chinese cohort); limited generalizability to South Asian or African populations
• The trial included patients already on beta-blockers/disopyramide — therefore reflects add-on therapy efficacy rather than monotherapy (MAPLE-HCM addressed monotherapy question in 2025)
• Not all patients had a dose response by week 8 — further dose adjustment algorithms may be refined in practice
• Impact of background LVEF variation (range 60–91%) on dose-response not fully characterized

Key Concepts Mentioned

• concepts/LVOTO — primary pathophysiology addressed; aficamten reduces dynamic LVOTO via sarcomere hypercontractility inhibition
• concepts/Septal-Reduction-Therapy — secondary endpoint: aficamten reduced SRT eligibility duration by 78 days vs placebo
• concepts/Calcium-Homeostasis-in-HCM — upstream mechanism; myosin inhibition reduces cross-bridge cycling → reduces Ca²⁺ demand

Key Entities Mentioned

• entities/Aficamten — drug under study; first phase 3 RCT evidence vs placebo in obstructive HCM
• entities/HCM — obstructive subtype; pharmacological management
• entities/Mavacamten — same drug class; comparison context

Wiki Pages Updated

• wiki/sources/aficamten-sequoiahcm-nejm-2024.md — created
• wiki/entities/Aficamten.md — SEQUOIA-HCM section added; source_count updated
• wiki/entities/HCM.md — SEQUOIA-HCM referenced in LVOTO management section
• wiki/concepts/LVOTO.md — SEQUOIA-HCM section added under pharmacological management
• wiki/concepts/Septal-Reduction-Therapy.md — SEQUOIA-HCM SRT eligibility reduction noted
• wiki/sourceindex.md — entry added
• wiki/wikiindex.md — Aficamten entity description updated