Abstract 176: Assessment of QT and JT Intervals in Bundle Branch Block: A New Formula
PURPOSE: QT interval prolongation in the surface ecg is a marker of abnormal repolarization. In patients with bundle branch block, the assessment of ventricular repolarization remains controversial. Use of special 2-parameters formulas for QTc and JTc has been proposed. However, the complexity of these formulas precludes its everyday clinical application. We have proposed (AHA 2012) a very simple formula for QT correction: QTc=2QT/((1+RR)). We hypothesized that the same formula JTc=2JT/((1+RR)) can be used for the evaluation of repolarization in patients with normal conduction and in patients with bundle branch block.
METHODS: We measured the QT interval in a sample of 1996 ECGs ( 106 BRD, 60 BRI, 34 indeterminate ventricular conduction delay), and then we calculate the QTc and JTc intervals using 2 correction ormulas (Bazett, and our new formula). We correlate the QTc and JTc values of each method with the heart rate (HR) and QRS duration (QRSD). An ideal correction should lead to a lack of correlation between JTc and HR and QRS duration.
RESULTS: As expected the QT interval, QT Bazett, and QT New correlate strongly with QRSD ( r= 0.5, 0.57, 0.59). The JT interval, JT Bazett, and JT New show a weaker correlation with QRSD ( r= -0.1, -0.28, -0.27). JT Bazett shows a significant correlation with HR ( r = 0,17, p<0.001), on the contrary JT New shows no correlation with HR ( r= 0.05, p=0.1).
CONLUSION: We propose a simple, reliable formula for the evaluation of JT interval in patients with normal conduction and in patients with bundle branch block.
- © 2013 by American Heart Association, Inc.