Abstract 3419: MRI Predictors of Exercise Capacity in Adult Patients after Atrial Correction for Transposition of the Great Arteries
Objective: The purpose of this study is to identify magnetic resonance imaging (MRI) factors associated with reduced exercise capacity in adult patients (pts) with transposition of the great arteries (TGA) after atrial switch repair.
Background: Adult TGA pts after atrial repair are at risk for reduced exercise capacity and impaired clinical status. This finding has been related to a reduced ability to increase stroke volume during exercise. Resting MRI markers of decreased exercise capacity have not been determined.
Methods: We identified 35 pts with TGA after atrial switch repair. Seventeen pts were excluded for contraindications to MRI or inability to exercise. Eighteen adult pts (44% male; mean age 27 ± 6.6 yrs) were prospectively evaluated. Sixteen pts were s/p Mustard repair and 2 pts s/p Senning. Cardiac MRI and cardiopulmonary exercise treadmill test (CPETT) were performed within a mean of 2 days of each other. MRI variables indexed to body surface area included systemic right ventricular (RV) and pulmonary morphologic left ventricular (LV) end-diastolic volume (EDVi), end-systolic volume (ESVi) and mass. Pearson’s correlation coefficient was used to assess the relationship of these measurements to peak oxygen consumption (pVO2) by CPETT.
Results: Mean RVEDVi was 98± 27 cc/m2. Mean RVEF was 56 ± 7%. Mean LVEDVi was 63 ± 18 cc/m2. Mean LVEF was 64 ± 8%. Mean pVO2 was 23 ± 4 mg/kg/min. Mean exercise time was 9.9 ± 2 minutes. All patients were in sinus rhythm. Respiratory quotient was > 1.0 for all studies. LV volume parameters (LVEDVi, LVESVi and stroke volume) correlated significantly with pVO2 (r=0.56, p=0.01; r=0.53, p=0.02; and r=0.52, p=0.03, respectively) and were highly correlated to each other (r=0.90, p<0.001). Only 44% of patients achieved 85% of maximum predicted heart rate; however, heart rate did not correlate with pVO2. Neither systemic RV volumes nor EF correlated with pVO2.
Conclusion: In pts with TGA after atrial correction, volume parameters of the pulmonary ventricle were the strongest predictors of peak VO2. Systemic RV function was not a predictor of exercise capacity. This finding suggests that reduced preload related to fixed transport through atrial systemic venous baffles may be the limiting factor in the exercise capacity for these pts.