Introduction In Tetralogy of Fallot (TOF) late after repair, severe pulmonary regurgitation (PR) places the patient at risk for right ventricular (RV) dilatation and failure, arrhythmia and sudden cardiac death. Criteria for pulmonary valve replacement continue to be debated. Dobutamine stress MR (DS-MR) may improve diagnostic sensitivity to detect early RV dysfunction. We sought to investigate safety, feasibility and haemodynamic effect of DS-MR.
Methods We prospectively recruited 28 adult patients referred for cardiac MR (age 32±15) with repaired TOF, RV dilatation and severe PR on echocardiography. Exclusion criteria: Contraindications to MR, history of arrhythmia, severely impaired left ventricular (LV) function, severe aortic valve disease, and severe pulmonary stenosis. Ventricular volumes (axial 2D cine SSFP) and pulmonary artery and aortic flows (phase contrast) were obtained at baseline and during dobutamine infusion of 10 mcg/kg/min (stage 1) and 20 mcg/kg/min (stage 2). DS-MR was stopped when systolic blood pressure >190 mmHg, heart rate >75% predicted (220-age) or if patients experienced significant side effects.
Results Of the 28 patients, 24 completed stage 1 DS-MR (two subject experienced claustrophobia and two had failure of VECG triggering secondary to frequent ventricular ectopics not present during baseline scanning. Four of these 24 patients could not progress to Stage 2, due to either minor dobutamine side effects (nausea or headache, n=2) or achievement of >75% maximum predicted heart rate (n=2). Twenty patients went on to complete stage 2 DS-MR and no additional side effects were observed. Two data sets at stage 2 were excluded from analysis due to incomplete volumetric measurements. The heart rate (cardiac index) increased from 66±6 bpm (2.9±0.4 l/min/m2) at baseline to 91±18 bpm (3.9±0.9 l/min/m2) at Stage 1 and 117±14 bpm (4.5±1 l/min/m2) at Stage 2 (p<0.01). Significant reduction in LV end diastolic (EDV) and end systolic volumes (ESV) is seen at dobutamine 10 and 20 (p<0.01). In the RV there is a less marked reduction in volumes at 10 while at 20 mcg dobutamine there is no significant change in ESV in a sub-group (p=0.63) (abstract 094 figure 1, abstract 094 figure 2).
Conclusions Our data show that high dose dobutamine stress MR is safe and well tolerated in patients with corrected TOF and significant PR. In the LV there is a clear reduction in volume at each level of dobutamine, whereas the RV showed less response at 10 mcg and in a sub-group failed to reduce RV-ESV at stage 2 DS-MR. The change in RV-ESV under stress may become a discriminative parameter in TOF patients being assessed for pulmonary valve replacement.
- Tetralogy of fallot
- dobutamine stress
- cardiac magnetic resonance