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

Abstract

Despite improved ventricular function after heart transplantation, the aerobic capacity, as measured by peak oxygen consumption (VO(2 peak)) 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 VO(2 peak) in younger HTRs is due to reduced left ventricular (LV) distensibility. 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 VO(2 peak). As expected, VO(2 peak) 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 VO(2 peak) 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). LV distensibility does not appear to be a major determinant of exercise intolerance in young HTR.