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.

No conflict of interest has been declared by the author(s).