Exercise Capacity in Patients with Pulmonary Atresia with Intact Ventricular Septum: Does the Type of Repair Matter?

Background: Patients with Pulmonary Atresia and Intact Ventricular Septum (PA/IVS) are managed surgically with either univentricular (Fontan) or biventricular (BV) repair depending on the degree of right ventricular hypoplasia. Although the biventricular repair is favored, there is limited data comparing the exercise capacity between the two types of repairs.

Methods: This single center retrospective review included patients with repaired PA/IVS who underwent comprehensive treadmill cardiopulmonary exercise testing including spirometry. Patients with 1 ½ ventricular repair for PA/IVS, other congenital heart defects, or incomplete data were excluded. Demographic data included gender, age, height, and weight at the time of exercise. Peak oxygen uptake (VO2 in ml/kg/min), an indicator of maximal aerobic capacity and peak heart rate, a measurement for chronotropy, were collected. Other parameters studied were a) Percentage of predicted VO2 (%VO2) normalized for age, weight, height, and gender b) % oxygen pulse c) anaerobic threshold, d) Chronotropic Index, e) Metabolic equivalents (METS), f) % Breathing reserve, g) Forced Vital capacity, h) % Forced Expiratory Volume in 1 second (FEV1), and i) Maximum voluntary ventilation (MVV). Chronotropic Index was calculated using the formula: [(peak heart rate–resting heart rate)/ (220–age–resting heart rate)]. Statistical analyses (SPSS version 20.0) included t-test to compare the various exercise parameters between the groups.

Results: A total of 35 patients (mean age 21± 8 years, male 43%) met our inclusion criteria. Demographics and pertinent findings comparing patients with univentricular (n=20) vs. biventricular (n=15) repair are mentioned in Table 1and Table 2 respectively. Patients who underwent univentricular (Fontan) repair had significantly lower, i) peak heart rate (149±29.6 vs. 179 ±17, p=0.001), ii) Chronotropic index (0.50±0.2 vs. 0.9±0.1, p=0.02), iii) %FVC (78.3±8.3 vs. 88.6±15.1, p=0.02), and iv) %FEV1 (75.0±9.8 vs. 87.3±10.4, p=0.002). No statistically significant difference was found in the %VO2 between the groups.

Conclusion: Patients with PA/IVS who underwent a univentricular (Fontan) repair demonstrated an objective impairment in their chronotropic and pulmonary function test parameters when compared to those with biventricular repair. However, this did not translate into a clinically significant difference in their exercise capacity. The findings of this exploratory study merit prospective longitudinal validation in a larger cohort of patients.