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A New Formula for Estimating the True QT Interval in Left Bundle Branch Block
Author(s) -
WANG BINHAO,
ZHANG LI,
CONG PEIXIN,
CHU HUIMIN,
LIU YING,
LIU JINQIU,
SURKIS WILLIAM,
XIA YUNLONG
Publication year - 2017
Publication title -
journal of cardiovascular electrophysiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.193
H-Index - 138
eISSN - 1540-8167
pISSN - 1045-3873
DOI - 10.1111/jce.13203
Subject(s) - qt interval , medicine , left bundle branch block , cardiology , qrs complex , bundle branch block , prolongation , electrocardiography , sinus rhythm , heart rate , heart failure , atrial fibrillation , blood pressure
A New QT Formula for LBBB Introduction QT prolongation is an independent risk factor for cardiac mortality. Left bundle branch block (LBBB) is more common in patients as they age. Widening of the QRS in LBBB causes false QT prolongation and thus makes true QT assessment difficult. We aimed to develop a simple formula to achieve a good estimate of the QT interval in the presence of LBBB. Methods and Results To determine the effect of QRS duration on the QT interval, QRS and QT were measured in sinus rhythm and during right ventricular apical pacing in 62 patients (age 55 ± 11 years, 60% male) undergoing electrophysiology studies. A QT formula for LBBB (QT‐LBBB) was derived based on the effect of increased QRS LBBB on QT LBBB . The predictive accuracy of the QT‐LBBB formula was then tested in 22 patients (age 66 ± 13 years, 64% male) with intermittent LBBB with comparisons to prior QT formulae and JT index. On average, the net increase in QRS LBBB constituted 92% of the net increase in QT LBBB . A new formula, QT‐LBBB = QT LBBB – (0.86 * QRS LBBB – 71), which takes the net increase in QRS LBBB into account, best predicted the QT interval with heart rate corrected QTc in the test set of LBBB ECGs when compared to the baseline value and prior formulae. Conclusion The QT‐LBBB formula developed in this study best estimates the true QT interval in the presence of LBBB. It is simple and therefore can be easily utilized in clinical practice.