Improved Exercise Capacity in Patients with Tetralogy of Fallot after Repair without Right Bundle Branch Block

Objectives: Prolonged QRS duration is pretty common in patients with tetralogy of Fallot (ToF) after repair. In addition, there is a correlation between grossly prolonged QRS duration and peak oxygen uptake (VO₂ peak) to sudden cardiac death or event-free survival. This study examined the impact of more subtle QRS prolongations on exercise capacity.

Methods: From February to November 2017, a total of 70 patients with ToF after surgical repair in early childhood (15.2 ± 4.7 years, 25 females) underwent a symptom limited cardiopulmonary exercise test. Before and at maximum effort QRS duration was measured in V1, V2, or V3. Data were analyzed via Student’s t-test for independent samples.

Results: Overall patients’ QRS duration was 130.6 ± 21.7 ms (range: 70–180 ms) and VO₂ peak was 31.0 ± 7.2 mL/min/kg (78.1 ± 16.0 VO₂ peak %predicted). Among them, a total of 10 patients had a QRS duration 100 milliseconds or smaller (normal atrioventricular conduction). Five had an incomplete right bundle branch block (iRBBB) from 101 to 119 milliseconds and 55 patients, a (complete) RBBB with a QRS duration of 120 milliseconds or longer. At maximum effort, QRS duration decreased to 94.1 ± 7.1% of the initial duration. None of the patients’ QRS duration increased during exercise. Comparison between patients with RBBB (QRS ≥ 120 milliseconds, n = 55) and no or incomplete RBBB (QRS: < 120 milliseconds, n = 15) showed significant differences in VO₂ peak % predicted (75.7 ± 15.6 vs. 86.9 ± 14.6%, p = 0.016). QRS duration decrease at exercise was similar and not related to RBBB (−8.9 ± 10.4 milliseconds in RBBB vs. −5.2 ± 8.0 milliseconds in no/iRBBB).

Conclusion: In the current area, a reasonable number of the patients have no RBBB after ToF repair. These patients with a normal QRS duration or an incomplete RBBB (QRS < 120 milliseconds) have a better exercise capacity compared with those with RBBB. Surgical repair strategies should also focus on protection the right Tawara branch.