Functional capacity by cardiopulmonary exercise testing is not related to health status in obstructive hypertrophic cardiomyopathy

Abstract Background In obstructive hypertrophic cardiomyopathy (HCM), the primary goal of therapy is to improve patient quality of life by decreasing symptom burden. Increasingly, cardiopulmonary exercise testing (CPET), with peak oxygen consumption (pVO2) and ventilator efficacy (VE/VCO2), is used to assess efficacy of novel therapies in clinical studies and selectively in clinical practice to determine treatments. However, the relationship of CPET variables to symptom burden in HCM is not well established. Therefore, we examined the relationship between CPET variables and health status measured by Kansas City Cardiomyopathy Questionnaire (KCCQ) and NYHA functional classification in a cohort of obstructive HCM patients. Methods Consecutive patients with HCM and resting left ventricular outflow tract (LVOT) obstruction (≥50 mmHg) underwent CPET between October 2022 to January 2024. Patients with a peak RER <1.0 were excluded (n=4). To investigate distribution of patient reported health status (KCCQ) and NYHA functional classification, patients were stratified into groups for pVO2 (<14, 14-20, and >20 mL/kg/min) to reflect moderate to severe, mild to moderate, and little to no functional limitation, respectively. Results Of 58 patients, clinical evaluation was at 59 ± 13 years of age, 55% male, with LVOT gradient of 83 ± 28 mmHg at rest with 84% NYHA class II or III and 76% with KCCQ overall summary (OS) <75. Both pVO2 and VE/VCO2 had significant but weak correlation with NYHA class and KCCQ scores (Table 1), with the strongest correlation observed with pVO2 and KCCQ-OS (R2= 0.13, p=0.004). In contrast, % predicted pVO2 was not significantly correlated with NYHA or KCCQ. Notably, despite 14 patients being classified as having little to no limitations by pVO2, 29% of these patients had mild to moderate disability and 29% had moderate to severe disability by KCCQ-OS (Figure 1). Conclusion In patients with symptomatic obstructive HCM, objective measures of exercise performance, including pVO2 and VE/VCO2, correlate poorly with measurements of health status. These data suggest that CPET results should not be considered a surrogate marker of heart failure symptom burden in obstructive HCM.