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QTc evaluation in patients with bundle branch block.

Harilaos Bogossian^1,2,3, Dominik Linz³, Jordi Heijman³

¹Department of Cardiology and Rhythmology, Ev. Krankenhaus Hagen, Hagen, Germany.

International Journal of Cardiology. Heart & Vasculature

|September 30, 2020

Summary

Measuring the QT interval in patients with bundle-branch blocks (BBB) is difficult. A modified QT interval formula (QTm = QT_BBB - 50% QRS_BBB) helps estimate true ventricular repolarization accurately.

Keywords:

JT interval Left bundle branch block Long QT QT formula QT interval Right bundle branch block

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Area of Science:

Cardiology
Electrocardiography

Background:

Accurate QT interval measurement on 12-lead ECG is challenging, especially with repolarization abnormalities, arrhythmias, or bundle-branch blocks (BBB).
BBB prolongs the QRS complex, consequently extending the measured QT interval and complicating the assessment of true ventricular repolarization.
Current US recommendations suggest focusing on the JT interval in BBB cases, but physicians are more familiar with QT interval interpretation.

Purpose of the Study:

To review the challenges in determining the QT interval in the presence of BBB.
To discuss the development and application of a modified QT interval formula for improved accuracy.

Main Methods:

Review of existing literature and clinical guidelines regarding QT interval measurement in BBB.
Explanation of the modified QT interval formula: QT_m = QT_BBB - 50% QRS_BBB.
Discussion of the subsequent application of rate-correction formulas.

Main Results:

The modified QT interval formula provides a practical method for estimating true repolarization time in BBB patients.
This formula accounts for the QRS prolongation caused by BBB, offering a more accurate assessment than standard QT measurements.
Physicians can utilize this formula, which builds upon familiar QT interval interpretation.

Conclusions:

The modified QT interval formula offers a valuable tool for accurately assessing ventricular repolarization in patients with BBB.
This approach simplifies interpretation for clinicians, enhancing the diagnostic utility of the ECG in complex cases.
Further adoption of this method can improve patient care by enabling more precise risk stratification related to QT interval abnormalities.