Key result
Accidentally induced right bundle branch block increased the mean QT interval by 34.83 ms, leading to a new practical correction formula: QT with RBBB minus 25% of QRS duration.
Why the study?
Prolonged QT interval in RBBB creates challenges in estimating repolarization time and eliminating the effect of depolarization changes.
Does a new formula based on QRS duration accurately correct the QT interval in patients with right bundle branch block?
Observational (n=96)
Does a new formula based on QRS duration accurately correct the QT interval in patients with right bundle branch block?
Mean Difference: 34.83
Absolute Event Rate: 404.22% vs 369.39%
A new, simple formula (QTwith RBBB − 25% × QRS) provides a rapid and practical method for correcting the QT interval in patients with right bundle branch block.
May aid QT correction in RBBB; leaves open prospective validation before clinical use.
Background and Aim Prolonging the QT interval in the right bundle branch block (RBBB) can create challenges for electrophysiologists in estimating repolarization time and eliminating the effect of depolarization changes on QT interval. In this study, we aimed to develop a practice formula to eliminate the effect of depolarization changes on QT interval in patients with RBBB. Methods This prospective study evaluated accidentally induced RBBB in patients undergoing electrophysiological study. Two expert electrophysiologists recorded the ECG parameters, including QRS duration, QT interval, and cycle length, in the patients. The formula was developed based on QT interval differences (with and without RBBB) and its proportion to QRS. Additionally, the Bazzet, Rautaharju, and Hodge formulas were used to evaluate QTc. Results We evaluated 96 patients in this study. The mean QT interval without RBBB was 369.39 ± 37.38, reaching 404.22 ± 39.23 after inducing RBBB. ΔQT was calculated as 34.83 ± 17.61, and the ratio of ΔQT/QRS with RBBB was almost 23%. Our formula is: (QTwith RBBB − 23% × QRS). Subtraction of 25% instead of 23% seems more straightforward and practical. Our formula could also predict the QTc interval in RBBB based on the Bazzet, Rautaharju, and Hodge formulas. Conclusion Previous formulas for QT correction were hard to apply in the clinical setting or were not specified for RBBB. Our new formula allows a rapid and practical method for QT correction in RBBB in clinical practice.
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Alizadeh et al. (2023) conducted an observational in Right bundle branch block (n=96). Accidentally induced right bundle branch block vs. Without right bundle branch block was evaluated on QT interval (MD 34.83). Accidentally induced right bundle branch block increased the mean QT interval by 34.83 ms, leading to a new practical correction formula: QT with RBBB minus 25% of QRS duration.
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