Does Maldistribution of Pulmonary Blood Flow Affect the Exercise Capacity in Patients with Repaired Tetralogy of Fallot? (RF_FR_302)

Tetralogy of Fallot(TOF) accounts for 9-14% of all congenital heart defects (1,4). The exercise capacity (XC) is decreased in patients with repaired Tetralogy of Fallot (rTOF). Patients with rTOF demonstrate abnormalities in branch pulmonary artery dimensions resulting in maldistribution of pulmonary blood flow (MPBF) (2,3). Cardiovascular magnetic resonance (CMR) imaging is the gold standard for assessing MPBF. There is a paucity of data regarding the impact of the MPBF on exercise capacity in this subset of patients (5). Therefore, the primary objective of our study was to assess the impact of MPBF on exercise capacity and its parameters in patients with repaired TOF. The secondary objective was to assess the impact of the maldistribution of pulmonary blood flow on the pulmonary function testing parameters.

Methods: In this single-center retrospective study, we enrolled patients with rTOF who underwent both comprehensive cardiopulmonary exercise stress test (CPET) and CMR within a 1-year interval. We excluded those with other congenital heart defects, stents in pulmonary arteries, and incomplete data. Demographics were collected. The following CPT parameters were collected: 1) Peak oxygen uptake (peak VO2 in ml/kg/min), an indicator of maximum aerobic capacity, 2) Percentage of predicted VO2 (%VO2) normalized for age, weight, height, and gender 3) % oxygen pulse 4) Percentage of predicted HR or %HR and 5) Heart rate at peak of exercise or HR. The abnormal XC was defined as VO2< 85%. MR Angiography (MRA) images were used to measure the cross-sectional area of the left pulmonary artery (LPA), and the right pulmonary artery (RPA). The phase-contrast method was used to measure the flow through both pulmonary artery branches. MPBF was defined as either one of the parameters (1) area measurements: LPA or RPA relative branch area of less than 30%, (2) flow analysis: LPA relative flow < 30% or RPA relative flow < 40%. Data were analyzed using SPSS and the Student t-test and Chi-square test were used to compare these two groups. A p-value < 0.05 was considered significant.

Results: Our cohort included 47 patients (45% male). There was no difference in age, height, and weight, at exercise between patients with (n=12; age 33.1±10.3 years) and without (n=35; age 27.5±10 years) MPBF. XC was also not significantly different between the two groups. However, MPBF was associated with a significant decrease in the %HR (92.7 ± 7.7 vs. 84.3 ± 18; p < 0.005).

Conclusion:

A significant 17/47 (36.1%) of our patient population had abnormal exercise capacity as defined. Although maldistribution of pulmonary blood flow was seen in 25.5% of patients with rTOF, it did not adversely impact all the exercise stress testing and pulmonary function testing parameters. Peak HR was significantly affected and decreased in patients with MPBF thereby indicating a decrease in the chronotropic index in patients with rTOF due to MPBF. We also observed an increase in oxygen consumption in patients with MPBF which is an interesting finding and needs further investigation. The findings of this exploratory study merit prospective longitudinal long-term validation in a larger population of patients.