Beyond Peak VO2: VO2T12.5% Emerges as a Cardiospecific Marker of Performance and Therapeutic Response in Obstructive HCM

Highlights

• VO2T12.5% (the time for VO2 to decline by 12.5% from peak) is established as a cardiospecific metric, correlating with exercise hemodynamics (PCWP/CO slope) rather than peripheral factors.
• Prolonged VO2T12.5% is a robust independent predictor of heart failure hospitalization and mortality, with a hazard ratio of 1.54 per 15-second increase.
• Treatment with the cardiac myosin inhibitor aficamten significantly accelerates VO2 recovery, with a mean improvement of 8 seconds compared to placebo.
• Improvements in recovery speed correlate directly with physiological markers of reduced obstruction, including lower LVOT gradients and decreased cardiac biomarkers.

Introduction

In the clinical assessment of heart failure (HF) and hypertrophic cardiomyopathy (HCM), peak oxygen uptake (pVO2) has long served as the gold standard for evaluating functional capacity. However, pVO2 is a composite metric influenced by various factors, including pulmonary function, skeletal muscle efficiency, and patient effort. The recovery phase following exercise—post-exercise oxygen uptake recovery (VO2Rec)—remains an underutilized but potentially more specific window into cardiac performance. Historically, slow VO2Rec has been associated with advanced heart failure, yet its cardiospecificity and responsiveness to disease-specific therapy have not been fully elucidated.

Obstructive hypertrophic cardiomyopathy (oHCM) presents a unique model for studying these recovery patterns. The condition is characterized by left ventricular outflow tract (LVOT) obstruction and impaired diastolic filling, both of which dynamically limit cardiac output during exertion. This substudy of the SEQUOIA-HCM trial aimed to establish a simplified recovery metric, VO2T12.5%, and evaluate its clinical utility as a marker of cardiac performance and a measure of therapeutic success with the novel cardiac myosin inhibitor, aficamten.

Study Design and Methodology

The investigation was conducted in two distinct phases. The first phase utilized the MGH-ExS (Massachusetts General Hospital Exercise Study) cohort, which included 814 patients referred for dyspnea on exertion. These participants underwent cardiopulmonary exercise testing (CPET) integrated with invasive hemodynamic monitoring. The goal was to validate the physiological relevance of VO2Rec patterns, specifically the time required for VO2 to decline by 12.5% (VO2T12.5%), 25%, and 50% of peak values.

The second phase applied these recovery metrics to the SEQUOIA-HCM trial, a pivotal Phase 3, randomized, double-blind, placebo-controlled study. This trial evaluated the efficacy of aficamten (a next-generation cardiac myosin inhibitor) in 282 patients with symptomatic oHCM. The substudy specifically analyzed 263 participants who completed CPET at both baseline and week 24. The primary objective was to determine if aficamten treatment could modify VO2T12.5% and if such changes correlated with improvements in cardiac structure and function.

Key Findings

Hemodynamic Validation of VO2T12.5%

Data from the MGH-ExS cohort provided critical evidence that the initial phase of VO2 recovery is uniquely tied to cardiac function. Patients with a prolonged VO2T12.5% (defined as 35 seconds or longer) exhibited significantly higher exercise pulmonary capillary wedge pressure (PCWP) to cardiac output (CO) slopes (P < 0.0001). This indicates that slow recovery in the first few seconds post-exercise is a marker of elevated filling pressures and impaired cardiac reserve. Notably, there was no significant difference in peripheral oxygen extraction between those with fast versus slow recovery (P = 0.11), suggesting that VO2T12.5% is more cardiospecific than other CPET variables.

Prognostic Significance

The study demonstrated that VO2T12.5% is not only a physiological marker but also a potent prognostic indicator. In the referral cohort, every 15-second increase in VO2T12.5% was associated with a 54% increase in the risk of heart failure hospitalization or all-cause death (Hazard Ratio 1.54; 95% CI, 1.35-1.76; P < 0.001). This prognostic value remained robust even after adjusting for traditional markers like pVO2 and the VE/VCO2 slope.

Impact of Aficamten on VO2 Recovery

In the SEQUOIA-HCM trial, the baseline mean VO2T12.5% was 45 seconds. At 24 weeks, patients treated with aficamten showed a significant improvement, with recovery times shortening by an average of 8 seconds relative to placebo (95% CI, -12 to -5 seconds; P < 0.001). Furthermore, participants in the aficamten group were 3.7 times more likely to achieve a clinically significant improvement of 15 seconds or more in their recovery time. The calculated number needed to treat (NNT) to achieve this 15-second improvement was only 4.8, highlighting the high therapeutic efficacy of the drug.

Expert Commentary and Mechanistic Insights

The findings from this substudy provide a physiological bridge between the mechanism of action of cardiac myosin inhibitors and functional recovery. By reducing excessive actin-myosin cross-bridge formation, aficamten alleviates LVOT obstruction and improves myocardial relaxation. This study suggests that these cellular changes translate into a faster return to baseline metabolic states after exertion.

The correlation between shortened VO2T12.5% and reductions in NT-proBNP and high-sensitivity cardiac troponin I is particularly telling. These biomarkers are surrogates for myocardial wall stress and injury, respectively. The fact that faster VO2 recovery tracks with these markers reinforces the theory that VO2T12.5% is a direct reflection of reduced cardiac strain. From a clinical perspective, the simplicity of calculating VO2T12.5%—requiring only standard CPET data without the need for invasive catheters—makes it an attractive candidate for routine clinical practice.

Conclusion

The SEQUOIA-HCM substudy successfully identifies VO2T12.5% as a novel, cardiospecific metric that captures aspects of exercise performance often missed by peak VO2 alone. Its ability to predict clinical outcomes and its responsiveness to aficamten therapy underscore its value in the management of obstructive hypertrophic cardiomyopathy. As clinicians look for more nuanced ways to assess patient progress and therapeutic response, the integration of VO2T12.5% into standard CPET protocols offers a promising, evidence-based approach to monitoring cardiac performance.

Funding and Clinical Trial Information

The SEQUOIA-HCM trial was supported by Cytokinetics, Inc. The study is registered at ClinicalTrials.gov with the identifier NCT05186818.

References

1. Campain J, et al. Characterization and Application of Novel Exercise Recovery Patterns That Reflect Cardiac Performance: A Substudy of the SEQUOIA-HCM Trial. Circulation. 2025 Oct 7;152(14):990-1002.
2. Maron MS, et al. Aficamten for Symptomatic Obstructive Hypertrophic Cardiomyopathy: SEQUOIA-HCM Main Results. J Am Coll Cardiol. 2024.
3. Lewis GD, et al. Standardized Reporting of Exercise Variables in Heart Failure. Circulation. 2017;136(21):e399-e423.