Left ventricular distensibility does not explain impaired exercise capacity in pediatric heart transplant recipients

BACKGROUND: Despite improved ventricular function after heart transplantation, the aerobic capacity, as measured by peak oxygen consumption (VO2peak) of pediatric heart transplant recipients (HTRs), remains 30% to 50% lower than age-matched healthy individuals. Research in adult HTRs suggests that diastolic dysfunction is a major determinant of exercise intolerance; however, it is unknown whether the impaired VO2peak in younger HTRs is due to reduced left ventricular (LV) distensibility. METHODS: Eight HTRs (mean age, 15 years; mean time post-transplant, 7 years) and 8 matched healthy controls were studied. To evaluate LV distensibility, echocardiographic measurements of ventricular volumes were obtained in 3 positions: supine, head-up tilt, and head-down tilt. Subsequently, participants underwent exercise stress testing to evaluate VO2peak. RESULTS: As expected, VO2peak was 26% lower in HTRs (p < 0.05). Ventricular volumes in each position were small in HTRs (p = 0.01); however, the percentage change in LV end-diastolic volume indexed (EDVi) to body surface area after the transition from supine to head-up tilt and from head-up tilt to head-down tilt were similar between HTRs (p = 0.956) and controls (p = 0.801). The change in EDVi during the transition from head-up tilt to head-down tilt (LV distensibility) strongly predicted VO2peak in patients (R-2 = 0.614, p = 0.021) and controls (R-2 = 0.510, p = 0.047). Importantly, the slope of this relationship did not differ between HTRs (1.01) and controls (0.977; p = 0.951). CONCLUSIONS: LV distensibility does not appear to be a major determinant of exercise intolerance in young HTR. J Heart Lung Transplant 2013;32:63-69 (C) 2013 International Society for Heart and Lung Transplantation. All rights reserved.