Stress increases intracardiac 4D flow cardiovascular magnetic resonance -derived energetics and vorticity and relates to VO₂max in Fontan patients

Background: We hypothesize that dobutamine-induced stress impacts intracardiac hemodynamic parameters and that this may be linked to decreased exercise capacity in Fontan patients. Therefore, the purpose of this study was to assess the effect of pharmacologic stress on intraventricular kinetic energy (KE), viscous energy loss (EL) and vorticity from four-dimensional (4D) Flow cardiovascular magnetic resonance (CMR) imaging in Fontan patients and to study the association between stress response and exercise capacity. Methods: Ten Fontan patients underwent whole-heart 4D flow CMR before and during 7.5 μg/kg/min dobutamine infusion and cardiopulmonary exercise testing (CPET) on the same day. Average ventricular KE, EL and vorticity were computed over systole, diastole and the total cardiac cycle (vorticity_vol_{avg cycle}, KE_{avg cycle}, EL_{avg cycle}). The relation to maximum oxygen uptake (VO₂ max) from CPET was tested by Pearson's correlation or Spearman's rank correlation in case of non-normality of the data. Results: Dobutamine stress caused a significant 88 ± 52% increase in KE (KE_{avg cycle}: 1.8 ± 0.5 vs 3.3 ± 0.9 mJ, P < 0.001), a significant 108 ± 49% increase in EL (EL_{avg cycle}: 0.9 ± 0.4 vs 1.9 ± 0.9 mW, P < 0.001) and a significant 27 ± 19% increase in vorticity (vorticity_vol_{avg cycle}: 3441 ± 899 vs 4394 ± 1322 mL/s, P = 0.002). All rest-stress differences (%) were negatively correlated to VO₂ max (KE_{avg cycle}: r = − 0.83, P = 0.003; EL_{avg cycle}: r = − 0.80, P = 0.006; vorticity_vol_{avg cycle}: r = − 0.64, P = 0.047). Conclusions: 4D flow CMR-derived intraventricular kinetic energy, viscous energy loss and vorticity in Fontan patients increase during pharmacologic stress and show a negative correlation with exercise capacity measured by VO₂ max.