Heart rate response during exercise predicts exercise tolerance in adults with transposition of the great arteries and atrial switch operation.

BACKGROUND: To assess the relationship between heart rate response and exercise tolerance in adults with systemic right ventricle (sRV) after atrial switch repair for Transposition of the Great Artery (TGA) in addition to other physiological parameters.

METHODS: All patients with a sRV after atrial switch repair for TGA followed in our institution between June 2015 and April 2018 who underwent cardiopulmonary exercise testing (CPET) were analyzed. Cardiac imaging performed within a six-month time period of the CPET were also collected. Chronotropic incompetence was defined as the inability to achieve 80% of age-predicted maximal heart rate reserve (HRR) and <62% on a beta-blocker regimen. Patient characteristics were assessed according to tertiles of the percentage of predicted pVO2 (%ppVO2).

RESULTS: We studied 70 patients (mean of age 32.4 ± 7.6 years old, 51 males). Mean peak oxygen uptake was 21.5 ± 5.8 mL/kg/min, corresponding to a %ppVO2 of 57 ± 14.1% while mean VE/VCO2 slope was 37.1 ± 8.2. There was a trend toward more exaggerated hyperventilation in patient with lower pVO2. Mean age-adjusted HRR was 68.5 ± 19%. Chronotropic incompetence was observed in 65.7% and was correlated with %ppVO2 (r = 0.482; p < 0.001) as physical training evaluated with Ventilatory Anaerobic threshold (r = 0.571; p < 0.001), while no difference was found based on respiratory parameters. No echocardiographic or Magnetic Resonance Imaging parameters assessing sRV systolic function at rest were correlated with %ppVO2.

CONCLUSIONS: Exercise limitation is related to the inability to increase cardiac output during exercise and is notably due to the degree of chronotropic incompetence.