In a significant advancement for cardiovascular medicine, the cardiac myosin inhibitor aficamten (Myqorzo) has demonstrated a clear clinical benefit for patients suffering from symptomatic nonobstructive hypertrophic cardiomyopathy (HCM). The findings, derived from the pivotal Phase III ACACIA-HCM trial, represent a landmark moment for a patient population that has historically lacked targeted, FDA-approved pharmacological interventions.
The results, presented at the European Society of Cardiology’s annual meeting and published simultaneously in the New England Journal of Medicine (NEJM), indicate that aficamten significantly improves both exercise capacity and patient-reported quality of life compared to a placebo.
The Clinical Landscape: Addressing a Therapeutic Gap
Hypertrophic cardiomyopathy is a complex, often genetic, condition characterized by the thickening of the heart muscle, which can impede the heart’s ability to pump blood effectively. While obstructive HCM—where the thickened muscle physically blocks blood flow—has seen therapeutic breakthroughs with myosin inhibitors, the nonobstructive form has remained a persistent challenge for clinicians.
"You have multiple domains of benefit that are reflecting on the patients, from symptoms, to patient-reported health status, exercise, and biomarkers," said Ahmad Masri, MD, of the Oregon Health & Science University Medical Group, who led the research. "Every way, shape, or form you look at this, there was benefit from aficamten in a disease that has no treatments available right now."
The ACACIA-HCM trial sought to determine whether the mechanism of aficamten—a selective cardiac myosin inhibitor designed to modulate heart contractility—could provide relief to the millions of patients living with the nonobstructive phenotype of this debilitating disease.
Chronology: From Concept to Clinical Milestone
The journey to this discovery began with the successful development of aficamten for the obstructive form of the disease. Following the drug’s FDA approval last December—buoyed by the positive data from the SEQUOIA-HCM trial—researchers pivoted to the nonobstructive cohort.
- Trial Design and Enrollment: The ACACIA-HCM trial enrolled 517 patients diagnosed with symptomatic nonobstructive HCM. Inclusion criteria were rigorous: participants required a left ventricular (LV) end-diastolic wall thickness of at least 15 mm (or 13 mm with a genetic predisposition or family history), a resting LV outflow tract gradient of less than 30 mm Hg, and a baseline left ventricular ejection fraction (LVEF) of 60% or higher.
- Methodology: The trial employed a double-blind, placebo-controlled design. Participants were randomized to receive either a placebo (n=259) or aficamten (n=258), beginning with a 5 mg dose that was titrated up to a maximum of 20 mg based on clinical response.
- Monitoring and Evaluation: The primary endpoints were measured at week 36. Patients were followed for a total of 72 weeks, concluding with a 4-week washout period.
- Data Presentation: The 36-week results were unveiled at the European Society of Cardiology meeting, marking the first time a therapy in this class has reached its dual primary endpoints for the nonobstructive population.
Supporting Data: Quantitative Evidence of Efficacy
The ACACIA-HCM trial was designed with dual primary endpoints to capture both objective physiological performance and the subjective patient experience.
Primary Endpoints
At the 36-week mark, the data showed statistically significant improvements for those on aficamten:
- Peak Oxygen Uptake: Patients in the treatment group showed a mean change in peak oxygen uptake of 0.64 mL/kg/min, compared to a slight decline of -0.03 mL/kg/min in the placebo group. The least-squares mean difference of 0.67 mL/kg/min (P=0.003) confirms a meaningful improvement in exercise capacity.
- Patient-Reported Outcomes: Using the Kansas City Cardiomyopathy Questionnaire clinical summary score (KCCQ-CSS), researchers recorded an average increase of 11.4 points in the aficamten group versus 8.4 points in the placebo group. The difference of 3.0 points (P=0.02) highlights the tangible relief patients experienced in their day-to-day symptoms.
Secondary Endpoints and Biomarkers
Beyond the primary metrics, the drug demonstrated consistent performance across secondary measures. Improvements were noted in New York Heart Association (NYHA) functional class, a comprehensive exercise Z-score, and levels of N-terminal pro-B-type natriuretic peptide (NT-proBNP), a key biomarker for wall stress and cardiac strain. A separate analysis, published in Circulation, further detailed the drug’s effectiveness across various domains, including diastolic function and symptom burden.
Safety Profile and Clinical Management
As with any therapeutic that modulates cardiac contractility, safety remains a paramount concern. Dr. Masri noted that while there were no unexpected safety signals, the nature of the drug requires careful monitoring.
- Adverse Events: Serious adverse events were reported in 20.2% of the aficamten group compared to 14.7% in the placebo group.
- Heart Failure Considerations: Heart failure occurred in 4.7% of the treatment group versus 1.2% in the placebo group. Notably, all such events occurred during the initial 12-week titration period and were successfully managed with diuretics.
- Ejection Fraction Monitoring: A reversible reduction in LVEF to below 50% was observed in 10.5% of the treatment group. Because aficamten works by modulating contractility, clinical protocols mandated down-titration of the drug if a patient’s LVEF dropped between 40% and 50%. Most patients were able to remain on the therapy at a lower dose.
Given the current FDA labeling for aficamten in obstructive HCM—which includes a boxed warning regarding LVEF reductions and the potential for systolic dysfunction—the trial reinforces the necessity of the existing Risk Evaluation and Mitigation Strategy (REMS). Clinicians must continue to perform echocardiograms prior to and during treatment to ensure patient safety.
Official Responses and Medical Implications
The medical community has greeted the ACACIA-HCM results with a mix of celebration and cautious scientific optimism.
Peer Perspective
Nosheen Reza, MD, of the University of Pennsylvania, served as the trial discussant and was quick to congratulate the research team. "This is a milestone; the first definitively positive trial in this population," she stated. However, she also provided essential context, noting that the magnitude of benefit in nonobstructive patients appears more modest than that observed in obstructive HCM cohorts.
Defining the Path Forward
Dr. Reza highlighted that the next phase of research must move beyond broad categories. "The opportunity now for us is to understand how treating nonobstructive HCM is not a single phenotype," she explained. "We must move towards better defining the mechanisms, patients, and therapeutic targets that determine clinical response."
The trial report acknowledged that while the KCCQ-CSS scores indicated a growing advantage over time, the long-term durability of these benefits beyond 36 weeks remains to be fully solidified. Researchers are currently looking to the ongoing FOREST-HCM open-label extension trial to provide more comprehensive data on the long-term impact of the therapy.
Conclusion: A New Era for HCM Patients
The ACACIA-HCM trial represents a watershed moment for cardiology. By proving that cardiac myosin inhibition can benefit patients with nonobstructive HCM, the trial has effectively expanded the reach of precision medicine in cardiology.
For patients who have long lived with the breathlessness, fatigue, and chest pain associated with this condition, aficamten offers more than just a reduction in biomarkers—it offers the potential for an improved quality of life. As clinicians continue to refine patient selection and titration protocols, the focus will shift from simply identifying that the drug works to understanding exactly who benefits most, ensuring that this innovative therapy is deployed safely and effectively across the diverse spectrum of hypertrophic cardiomyopathy.
With the data now published in the NEJM and the Circulation analysis providing deeper insights, the cardiology community has a robust foundation upon which to build. The future of HCM treatment is no longer limited to managing symptoms; it is now actively targeting the underlying molecular drivers of the disease.
