QTc interval evaluation in patients with right bundle branch block or bifascicular blocks

BACKGROUND: The right bundle branch block (RBBB) and the bifascicular blocks affect QRS duration in the right precordial leads, which are usually used for QT interval determination. Up to now, there is no clear recommendation how to determine QT interval in patients with RBBB or bifascicular block. HYPOTHESIS: The hypothesis of the present study was to evaluate the feasibility of a simple formula for RBBB and bifascicular block correction, thereby making it easier to determine the QTc interval. METHODS: In patients with intrinsic QRS duration <120 ms, artificial RBBB with either left posterior (LPFB) or left anterior fascicular block (LAFB), created by left ventricular pacing maneuvers, were corrected using the Bogossian formula (QTm) and afterward were heart rate corrected (QTmc). Heart rate correction was performed using different heart rate formulas in comparison to each other. The QTmc intervals were compared in each patient with the QTc interval during intrinsic rhythm. RESULTS: A total of scheduled 71 patients were included in this prospective multicenter observational comparative study. Compared to intrinsic QTc interval, the mean ΔQTmc interval by combination of the Bogossian and the Hodge formulas was −3 ± 24 ms in RBBB + LPFB (P = .44) and −6 ± 25 ms in RBBB + LAFB (P = .15). The Bogossian formula showed a significant deviation from the actual QTc interval with both the Bazett and the Fridericia formulas. CONCLUSION: In combination with the Hodge formula, the Boggosian formula delivered the best results in comparing the true QTc interval in narrow QRS with the QTmc interval in the presence of a bifascicular block.