Title: What factors influence exercise capacity (VO2peak) in adolescents with Tetralogy of Fallot?
Thesis Supervisor: Dr. William Sheel
Committee members: Ms. Astrid De Souza, Dr. David Wright, Dr. Kathryn Armstrong
Defence Chair: Dr. Cameron Mitchell
Abstract:
BACKGROUND: Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart defect. Infants with TOF typically receive surgical correction shortly after birth. Despite undergoing surgery, their exercise capacity (VO2peak) remains reduced. PURPOSE: This study explores the interplay between surgical, physiological and behavioural factors in adolescents with TOF.
HYPOTHESIS: We hypothesized that a worse surgical course – indicated by having postoperative complication and extended hospital stay – along with left and right ventricular systolic dysfunction and lower levels of recreational physical activity would result in reduced % predicted VO2peak.
METHODS: A single-centre, retrospective review (January 2016 – September 2024) of TOF patients aged 11-18 who completed a maximal cardiopulmonary exercise test (CPET) within 6 months of their most recent resting echocardiogram (echo). Additional prospective data was collected: TOF adolescents aged 11 – 18 were recruited between May 2024 – October 2024. Along with standard echo, CPET, recreational physical activity levels, and sports participation data, adolescent participants also completed a motor skills (BOT-2 SF) assessment, and their parents filled out two questionnaires on their own physical activity levels.
RESULTS: The median age at primary repair was 7.6 months (5.3-11.7), with the transannular patch surgical technique accounting for 65%. Participants (15.8 years, 14.2-17.5) had a lower % predicted VO2peak (93, 64-91) compared to healthy adolescents, HRpeak (181bpm, 177-191), O2pulse peak (10.2ml/beat, 8.7-13.4) and OUESkg (36.5,28.3—42.9). VE/VCO2 slope was elevated (36.5,34.8 – 40.1). 64% of participants participated in recreational activity at least 2 days per week, and 18% participated in competitive sports. Statistical analysis identified the following predictor variables for % predicted VO2peak: the occurrence of postoperative complications, hospital length of stay (LOS), body mass index (BMI), mitral valve (MV) A wave velocity, the number of recreational physical activity participation days and involvement in competitive sports. The final model explained for 80.3% of the variance in % predicted VO2peak, where BMI (p<0.001), MV A wave velocity (p=0.0003) and competitive sports (<0.001) were significant predictors.
CONCLUSION: Adolescents with TOF have a lower VO2peak which can be explained by body composition, left ventricular compliance, and involvement in competitive sports.