Dobutamine-induced increase of right ventricular contractility without increased stroke volume in adolescent patients with transposition of the great arteries: evaluation with magnetic resonance imaging.

OBJECTIVE: Prognosis in patients with surgically corrected (Senning or Mustard) transposition of the great arteries (TGA) depends mainly on right ventricular (RV) function and RV functional reserve. We examined the role of dobutamine stress in the early detection of RV dysfunction in asymptomatic or slightly symptomatic patients with TGA using magnetic resonance imaging (MRI). DESIGN AND PATIENTS: Twelve asymptomatic or slightly symptomatic patients with chronic RV pressure overload, surgically corrected (Mustard or Senning) TGA (age 22.8 (+/- 3.4) years; New York Heart Association (NYHA) class I/II) and nine age matched healthy volunteers (age 27.3 (+/- 4.4) years) were included. MRI was applied both at baseline and during dobutamine stress (start dose 5 microg/kg/min to maximum dose 15 microg/kg/min) to determine RV and left ventricular (LV) stroke volumes (SV) and ejection fraction (EF).
RESULTS: At baseline only RVEF was significantly higher in controls than in patients (71 (+/- 9) vs. 57 (+/- 10)%, p < 0.001), other RV parameters were not significantly different between the two examined groups: RVSV (86 (+/- 21) vs. 72 (+/- 27) ml, p = ns), RV end-diastolic volume (EDV) (123 (+/- 37) vs. 123 (+/- 33) ml, p = ns), and heart rate (61 (+/- 10) vs. 69 (+/- 14) bpm, p = ns), respectively. During dobutamine stress RVEF increased significantly both in controls and patients (20 (+/- 16) vs. 17 (+/- 18)%, p < 0.01 and p < 0.02 vs. rest, respectively), but stress RVEF was significantly higher in controls than in patients (85 (+/- 3) vs. 66 (+/- 7)%, p < 0.0001). RVSV increased significantly in controls (22 (+/- 19)%, p < 0.02), and there was no significant increase in RVSV in patients (-10 (+/- 28)%, p = ns). The controls showed no change in RVEDV (2 (+/- 17)%, p = ns), but in patients a significant decrease in RVEDV (-24 (+/- 15)%, p < 0.001) was observed. Maximal heart rate was significantly higher in patients than in controls (122 (+/- 20) vs. 101 (+/- 14) bpm, p < 0.02).
CONCLUSION: In asymptomatic or slightly symptomatic patients with surgically corrected TGA dobutamine had a positive inotropic effect on RV, but the increased contractility was not accompanied by an appropriate increase in SV. Our data suggest inadequate RV filling in this category of patients, possibly due to rigid atrial baffles and compromised atrial function or decreased compliance due to RV hypertrophy.