title: Left ventricular distensibility does not explain impaired exercise capacity in pediatric heart transplant recipients.
abstract: BACKGROUND
  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.
  
  
  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 VO(2 peak).
  
  
  RESULTS
  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).
  
  
  CONCLUSIONS
  LV distensibility does not appear to be a major determinant of exercise intolerance in young HTR.
authors.affiliation: Stollery Children's Hospital, University of Alberta, Edmonton, Alberta, Canada. luis.altamiranodiaz@lhsc.on.ca
authors.forename: Luis A
authors.initials: LA
authors.lastname: Altamirano-Diaz
authors.forename: Michael D
authors.initials: MD
authors.lastname: Nelson
authors.forename: Lori J
authors.initials: LJ
authors.lastname: West
authors.forename: Nee S
authors.initials: NS
authors.lastname: Khoo
authors.forename: Ivan M
authors.initials: IM
authors.lastname: Rebeyka
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Haykowsky
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D017079:Exercise Tolerance; D005260:Female; D016027:Heart Transplantation; D006352:Heart Ventricles / Q000503:physiopathology*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male