Biventricular pacing in patients with Tetralogy of Fallot: non-invasive epicardial mapping and clinical impact

Introduction: Patients who have undergone repair of Tetralogy of Fallot (TOF) often present with right bundle branch block. Cardiac resynchronization therapy (CRT) with right ventricular (RV) or biventricular (BiV) stimulation has been proposed as a modality to correct electrical abnormalities and improve cardiac contractility in patients with repaired TOF. We aimed to 1) compare ventricular electrical activation in adults with repaired TOF during RV versus BiV stimulation, using a non-invasive epicardial mapping system, and 2) examine the clinical mid-term effects of BiV resynchronization.

Methods: 9 adults with repaired TOF were implanted with a CRT system and underwent 1) a non-invasive epicardial mapping (n=9) during sinus intrinsic rhythm, RV and BiV pacing 2) a clinical evaluation (n=7) before and after 6 months CRT with assessment of NYHA class and exercise capacity.

Results: During intrinsic rhythm, non-invasive mapping demonstrated delayed activation of the right compared with the left ventricle in all patients, with the greatest activation delay noted near the infundibulum. However, we observed important differences among patients, in the severity of activation delays. Global activation time and an index of dyssynchrony were improved (p<0.05) during BiV pacing compared with RV pacing and spontaneous rhythm. BiV pacing increased (p<0.05) exercise tolerance and lowered the mean NYHA functional class at 6 months of follow up.

Conclusion: Patients with corrected TOF present with different patterns of ventricular activation. RV stimulation modestly improved RV activation sequence and was associated with a delayed LV activation. Biventricular stimulation significantly decreased right and left ventricular dyssynchrony.