Coronary flow reserve as a marker of cardiac function, functional capacity and events in hypertrophic cardiomyopathy

Aim We examined the relationship between non-invasive coronary flow reserve (CFR) of the left anterior descending artery (LAD) and key echocardiographic and cardiopulmonary exercise testing (CPET) parameters, along with its predictive value for cardiac events in patients with hypertrophic cardiomyopathy (HCM). Methods Echocardiography along with CFR for LAD and CPET were performed in patients with symptomatic non-obstructive HCM during phase II, randomized, open-label multicentre study within two days in-between. CFR was calculated as the ratio of hyperaemic (after 140 mcg/kg/min adenosine) to baseline flow velocity. Patients were followed for 36 months through hospital and outpatient chart reviews to track cardiac events. The primary endpoint was to assess the association of CFR with 1) echo parameters [left ventricular outflow tract gradient, LV end-systolic volume (LVVs), and diastolic septal thickness (IVSd)]; and 2) CPET parameters [peak oxygen consumption (peak VO2)]; oxygen pulse, minute ventilation (VE)/carbon-dioxide (CO2) production slope]. The secondary endpoint was to evaluate the predictive value of CFR for cardiac deaths and the composite outcome of death and cardiac hospitalizations. Results Of 115 screened patients, 61 (52±14 years, 43% women) were included. CFR correlated with IVSd, LVVs, peak VO2, oxygen pulse, VE/VCO2 slope (r=-0.3, 0.1, 0.4, 0.4, -0.2; p=0.03, 0.01, 0.001, 0.001, 0.02, 0.03 respectively). In multivariate regression analysis, among all relevant echo and CPET variables, only oxygen pulse and CFR remained in the predictive equation for the occurrence of the composite outcome (Chie square=9.9, p=0.02), whereas VE/VCO2 slope remained the best predictor of cardiac deaths (Chie square=5.7, p=0.017). Conclusion CFR assessed by echocardiography is linked to LV systolic function, functional capacity, and ventilatory efficiency, and offers predictive value for composite cardiac event occurrence in patients with HCM, surpassing traditional prognostic markers.