HCM Treatment Advances: Why Patient Outcomes Lag Behind

The promise of disease modification in hypertrophic cardiomyopathy (HCM) has hit a snag. The highly anticipated ODYSSEY-HCM trial, evaluating mavacamten in patients with non-obstructive HCM (nHCM), demonstrated striking improvements in cardiac biomarkers and structural remodeling, yet failed to translate into meaningful clinical benefit as measured by exercise capacity or patient-reported symptoms. This disconnect underscores a critical challenge in HCM: targeting the underlying myocardial dysfunction isn’t always enough to alleviate the complex constellation of symptoms patients experience.

For decades, treatment of HCM has been largely palliative, focused on symptom management with beta-blockers and calcium channel blockers. The success of cardiac myosin inhibitors like mavacamten in obstructive HCM (oHCM) – dramatically reducing the left ventricular outflow tract obstruction – sparked hope for a disease-modifying therapy in the more common nHCM. The logic was compelling: nHCM often presents with diastolic dysfunction, impaired exercise capacity, and biomarker elevations suggestive of cardiac stress. Mavacamten, by reducing myocardial contractility, was hypothesized to alleviate these issues. The earlier MAVERICK-HCM phase 2 study provided encouraging signals, demonstrating biomarker improvements, which fueled the optimism leading into ODYSSEY-HCM.

However, ODYSSEY-HCM revealed a crucial difference. While mavacamten demonstrably altered the underlying cardiac biology – reducing wall thickness, left atrial size, and improving diastolic parameters – these changes didn’t translate into improved peak VO₂ or Kansas City Cardiomyopathy Questionnaire Clinical Summary Scores (KCCQ-CSS). Importantly, the placebo arm also showed improvement in these clinical endpoints, diluting the treatment effect. Several factors likely contributed to this. The complex pathophysiology of nHCM, involving diastolic dysfunction, microvascular ischemia, and impaired energetics, means that simply reducing hypercontractility may not be sufficient. Furthermore, the study population had a mean disease duration of 10 years, suggesting that significant structural remodeling and comorbidities may have already limited the potential for reversal.

The observed decline in LVEF in a substantial portion of mavacamten-treated patients (21.5% vs. 1.7% in placebo) also presents a clinical hurdle. This necessitated dose interruptions, potentially hindering the sustained sarcomere modulation needed for clinical benefit. Interestingly, aficamten, another myosin inhibitor, has shown a more favorable safety profile in early trials, and the ongoing ACACIA-HCM trial will be critical in determining if it can overcome the challenges faced by mavacamten in nHCM.

The Forward Look

The ODYSSEY-HCM results are not a dead end, but a course correction. The clear biologic response to mavacamten in nHCM validates the concept of sarcomere modulation, but highlights the need for a more nuanced approach. Several key areas warrant further investigation. First, better patient phenotyping is crucial. Identifying subgroups of nHCM patients most likely to benefit from myosin inhibition – perhaps those with less advanced disease or specific patterns of diastolic dysfunction – could improve trial outcomes. Second, combination therapies targeting multiple aspects of the disease pathophysiology, such as microvascular dysfunction or myocardial energetics, may be necessary. Finally, earlier intervention, before irreversible structural remodeling occurs, could maximize the potential for disease modification. The focus will likely shift towards identifying biomarkers that predict response to therapy, and potentially utilizing cardiac MRI to assess myocardial fibrosis and guide treatment decisions. The success of aficamten in the REDWOOD-HCM trial, and the ongoing ACACIA-HCM trial, will be pivotal in shaping the future of nHCM treatment. For now, guideline-directed medical therapy remains the standard of care, but the search for a truly disease-modifying therapy continues, informed by the lessons learned from ODYSSEY-HCM.