Increase of Right Ventricular Stroke Volume during Dobutamine Stress Magnetic Resonance: Relation to Lung Perfusion and Peak Oxygen Uptake in Young Adults after Neonatal Arterial Switch Operation in Transposition of the Great Arteries

Objectives: Monocentric prospective study to evaluate the effects of abnormal pulmonary perfusion on right ventricular stroke volume (RVSV) increase during DSMR and on cardiopulmonary exercise capacity.

Methods: Seventy-one unselected patients (age 18–29 years) underwent CMR at rest and under a standardized dobutamine stress protocol (10–20–30–40 µg/kg/min). Pulmonary blood flow distribution (PBFD) and RVSV were derived from phase contrast mapping in the main, right, and left pulmonary arteries (PAs) at each stress level. A cardiopulmonary exercise test (CPET, DGPK bicycle protocol) was performed at the same day. All patients reached maximal exercise effort according to heart rate and respiratory exchange rate.

Results:

PBFD at rest:

Out of 71, 7 patients (ASO-S) had abnormal pulmonary perfusion, defined as PBFD >2:1 and/or relevant stenosis of the main, right, or left PA (>2.5 m/s). Out of 71, 64 patients had normal pulmonary perfusion (ASO-N).

PBFD under DSMR:

1. In the whole patient group, there was no worsening compared with PBFD at rest. On individual patient level, no worsening of abnormal PBFD was found.

2. Under low-dose dobutamine, ASO-S had a significantly lower increase of RVSV (RVSVstress/RVSVrest) compared with ASO-N (1.04 vs. 1.20; p = 0.001). However, under high-dose dobutamine, this effect was not present any more (0.77 vs. 0.83, p = 0.22).

3. The increase of RVSV under low-dose and high-dose dobutamine did not correlate with peak oxygen uptake during CPET, neither in the total group nor in the subgroups (ASO-N, ASO-S). Peak oxygen uptake was not significantly different between ASO-N and ASO-S.

Conclusion:

1. Compared with patients without stenosis (ASO-N), patients with a relevant stenosis of the central PAs and/or abnormal peripheral blood flow distribution (ASO-S) had a reduced increase of RVSV under low-dose dobutamine stress, but not under high-dose dobutamine stress.

2. These findings did not correlate with peak oxygen uptake during CPET, an objective parameter of cardiopulmonary exercise capacity.

3. Therefore, a conservative proceeding with respect to interventional or surgical therapy especially in asymptomatic adult patients with nonsevere pulmonary artery stenosis or abnormal PBFD after neonatal arterial switch operation should be considered.