The Threshold for a Clinically Meaningful Improvement in Cardiopulmonary Exercise Testing Measures for Patients With Symptomatic Obstructive Hypertrophic Cardiomyopathy

BACKGROUNDPeak oxygen uptake (pVO2) is a strong, independent predictor of adverse cardiovascular outcomes, supporting cardiopulmonary exercise testing as a primary end point assessing efficacy of novel drug therapies in obstructive hypertrophic cardiomyopathy (oHCM) clinical trials. However, characterizing changes in pVO2 that patients perceive as beneficial or meaningful (ie, minimal important difference [MID]) has not been determined. METHODSData from patients with symptomatic oHCM enrolled in SEQUOIA-HCM and MAPLE-HCM were pooled. A total of 282 patients were randomized 1:1 to aficamten (5-20 mg daily) or matching placebo in SEQUOIA-HCM, and 175 patients were randomized 1:1 to aficamten (5-20mg daily) or to metoprolol (50-200 mg) in MAPLE-HCM; follow-up in both trials was 24 weeks. Primary outcome was change from baseline to week 24 ({Delta}) in pVO2 using Patient Global Impression of Change with anchor-based analysis to define MID. RESULTSAt week 24, {Delta}pVO2 (mL/kg/min) that corresponded to no change, one-category improvement, and one-category worsening were -0.05 (95% CI, -0.58 to 0.48), +0.35 (95% CI, -0.22 to 0.91), and -0.61 (95% CI, -1.36 to 0.13), respectively. Similarly, minute ventilation to carbon dioxide production ratio (VE/VCO2) slope that corresponded to no change, one-category improvement, and one-category worsening were 0.16 (95% CI, -0.59 to 0.90), -1.15 (95% CI, - 1.89 to -0.42), and 0.88 (95% CI, -0.42 to 2.19), respectively. In a responder analysis using this new threshold for pVO2, 60% of patients receiving aficamten achieved a {Delta}pVO2 [&ge;]0.35 versus 31% of patients on placebo or metoprolol (odds ratio, 3.4 [95% CI, 2.3-4.9], P<0.001). Consistent findings were seen with VE/VCO2 responder analysis. CONCLUSIONSChanges in pVO2 of +0.35 and -0.61 mL/kg/min were associated with a small but perceptible clinical improvement and worsening, respectively, in patients with oHCM. Applying this newly defined threshold resulted in excellent differentiation of treatment effect in a clinical trial. These novel data provide a measure of clarity to patients and clinicians regarding the interpretation of changes in pVO2 following therapeutic interventions, with potential impact on HCM management strategies and future clinical trials. Clinical Trial RegistrationSEQUOIA-HCM (NCT05186818; https://clinicaltrials.gov/study/NCT05186818?term=sequoia-hcm&rank=1); MAPLE-HCM (NCT05767346; https://clinicaltrials.gov/study/NCT05767346?term=maple-hcm&rank=1) Clinical PerspectiveO_ST_ABSWhat Is New?C_ST_ABSO_LIUsing pooled data from over 440 patients with symptomatic obstructive hypertrophic cardiomyopathy enrolled in two phase 3 clinical trials, we define, for the first time, the minimally important difference for peak oxygen uptake (pVO2) and ventilatory efficiency (VE/VCO2) using patient-anchored and distribution-based methodologies. C_LIO_LIA change in pVO2 of +0.35 mL/kg/min and a change in VE/VCO2 of -1.15 represent the minimal thresholds associated with patient-perceived clinical improvement. C_LIO_LIResponder analyses using these thresholds demonstrated robust differentiation between aficamten and placebo/metoprolol, with an odds ratio exceeding 3 for achieving a meaningful improvement in pVO2. C_LI What Are the Clinical Implications?O_LIThese newly defined thresholds bridge the gap between statistically significant changes in cardiopulmonary exercise testing measures and clinically meaningful benefit as perceived by patients with obstructive hypertrophic cardiomyopathy. C_LIO_LIClinicians can use these benchmarks to contextualize individual patient responses to medical therapy, informing shared decision-making regarding treatment continuation or modification. C_LIO_LIThese data provide a standardized, patient-centered framework for designing and interpreting primary end points in future hypertrophic cardiomyopathy clinical trials. C_LI