Non-invasive stroke volume assessment during cardiopulmonary exercise testing provides additional insight beyond O2-pulse in hypertrophic cardiomyopathy

In hypertrophic cardiomyopathy (HCM), cardiopulmonary exercise testing (CPET) is considered the gold standard for assessing exercise tolerance, with O2-pulse commonly used as a surrogate for stroke volume (SV). However, because SV reduction can be masked by increased oxygen extraction, direct non-invasive measurement of SV is valuable. This study involved 102 HCM patients (mean age 53 ± 16 years, 78% male), predominantly with a non-obstructive phenotype (74%), who underwent CPET with SV measurement using Physioflow (PF). Abnormal O2-pulse kinetics were observed in 12 patients, all confirmed by abnormal SV trends with PF. Additionally, PF identified another 28 patients with altered SV kinetics. Abnormal SV trends were associated with higher peak VE/VO2 ratios (42.6 [37.4–47.5] vs. 38.0 [33.6–41.3]) and lower end-tidal CO2 values (31.8 ± 4.9 vs. 34.3 ± 5.6 mmHg, p < 0.05). Patients with greater SV growth during the final 25% of exercise showed improved anaerobic threshold VO2 (49.8 ± 12.3% vs. 43.9 ± 15.2% predicted peak VO2), VO2/work slope (10.2 ± 2.0 vs. 9.3 ± 1.3 mL/min/Watt), and peak PetCO2 (34.5 ± 5.6 vs. 32.3 ± 5.2 mmHg), alongside a lower VE/VCO2 slope (28.7 [24.9–31.0] vs. 31.3 [27.3–34.2], p < 0.05). Integrating PF and CPET may enhance the detection of abnormal SV kinetics, which are associated with reduced functional capacity in HCM patients.