O2pulse Trajectory As An Indicator Of Cardiorespiratory Fitness In Adults With Congenital Heart Disease

Peak oxygen pulse (O2pulse) obtained with cardiopulmonary exercise testing (CPET) is defined as the ratio of oxygen uptake to heart rate (HR) at peak exercise. A surrogate for exercise stroke volume and arteriovenous O2 difference, O2pulse has prognostic value in adults with congenital heart disease (ACHD), but less is known about the significance of the O2pulse trajectory, an analysis of its kinetic response during CPET. PURPOSE: Determine significance and correlates of abnormal O2pulse trajectory in ACHD. METHODS: A retrospective analysis of ACHD patients who underwent CPET (including pre-exercise spirometry) and cardiac magnetic resonance (CMR) within ≤1-year apart as part of clinical evaluation at an ACHD specialty center. The O2pulse trajectory was defined as normal (normal curvilinear pattern) or abnormal (flat or decreasing trajectory) throughout the entire exercise period by visual assessment of a CPET expert. The results are reported as mean [SD] or number (%). Group differences (normal vs. abnormal O2pulse trajectory) were evaluated with independent samples T-tests for continuous variables or chi-square tests for nominal variables. RESULTS: CPET data of N = 217 ACHD patients included the following characteristics: 57% female, 75% white race, 36.2 [12.2] years of age, and body mass index (BMI; 28.4 [6.9] kg/m2). Within this group, a cohort of 132 patients (61%) had CMR within 1-year. 46% had abnormal O2pulse trajectory with Tetralogy of Fallot (n = 42 [19] %) being the most common lesion type. The CPET parameters of VO2peak (24.1 [9.9] vs. 20.5 [5.7] mL·kg-1·min-1) and peak O2pulse (13.1 [4.1] vs. 10.5 [3.0] mL/beat) were significantly lower in the abnormal O2pulse trajectory cohort with P < 0.001. Pre-exercise spirometry results of FVC-% and FEV1-% were lower in abnormal O2pulse trajectory cohort; P = 0.012, P = 0.010 respectively. Similarly, LV cardiac output (LVCO; P = 0.015), LV and RV ejection fraction (LVEF; P = 0.017 and RVEF; P < 0.001) were significantly lower. Age, sex, race, lesion type, BMI, hemoglobin levels, O2 saturations (SpO2), or use of beta-blocker was not different between groups (all P > 0.05). CONCLUSIONS: An abnormal O2pulse trajectory in ACHD is associated with lower cardiorespiratory fitness and reduced cardiac function and may have clinical significance in CPET interpretation. Dr. Canada is supported by a K23HL159270 grant from the National Heart, Lung, and Blood Institute.