Exercise oxygen pulse kinetics in patients with hypertrophic cardiomyopathy

19Objectives Reduced cardiac output (CO) has been considered crucial in symptoms' genesis in hypertrophic cardiomyopathy (HCM). Absolute value and temporal behaviour of O-2-pulse (oxygen uptake/heart rate (VO2/HR)), and the VO2/work relationship during exercise reflect closely stroke volume (SV) and CO changes, respectively. We hypothesise that adding O-2-pulse absolute value and kinetics, and VO2/work relationship to standard cardiopulmonary exercise testing (CPET) could help identify more exercise-limited patients with HCM. Methods CPETs were performed in 3 HCM dedicated clinical units. We retrospectively enrolled non-end-stage consecutive patients with HCM, grouped according to left ventricle outflow tract obstruction (LVOTO) at rest or during Valsalva manoeuvre (72% of patients with LVOTO = 50 mm Hg). We evaluated the CPET response in HCM focusing on parameters strongly associated with SV and CO, such as O-2-pulse and VO2, respectively, considering their absolute values and temporal behaviour during exercise. Results We included 312 patients (70% males, age 49 +/- 18 years). Peak VO2 (percentage of predicted), O-2-pulse and ventilation to carbon dioxide production (VE/VCO2) slope did not change across LVOTO groups. Ninety-six (31%) patients with HCM presented an abnormal O-2-pulse temporal behaviour, irrespective of LVOTO values. These patients showed lower peak systolic pressure, workload (106 +/- 45 vs 130 +/- 49 W), VO2 (21.3 +/- 6.6 vs 24.1 +/- 7.7 mL/min/kg; 74%+/- 17% vs 80%+/- 20%) and O-2-pulse (12 (9-14) vs 14 (11-17) mL/beat), with higher VE/VCO2 slope (28 (25-31) vs 27 (24-31)) (p