Machine read frontal QRS-T angle and QTc is no substitute for manual measurement of QTc in pro-arrhythmic drug overdose.

ABSTRACT

INTRODUCTION: To investigate whether there is an association between the blocking of cardiac potassium channels, which is characterised by a prolonged QTc interval and the frontal QRS-T angle after overdose by QT prolonging drugs. METHODS: We obtained patient medical records associated with QT prolonging drugs from 3 different hospitals the Calvary Mater Newcastle Hospital (CMNH), Royal Prince Alfred Hospital (RPAH) and Prince of Wales Hospital (POWH). RPAH and POWH admissions were taken between 4/01/2017 to 1/11/2019, and CMNH admissions were taken between 4/01/2013 to 24/06/2018. Demographic information and details of overdose were collected. All admission ECGs were manually measured. Linear regression was used to assess the relationship between various QTc formulas and the frontal QRS-T angle. A Bland-Altman plot was used to examine agreement between manual and machine QT intervals. RESULTS: 144 patients met the inclusion criteria for analysis. None of the patients developed torsades de pointes (TdP). There was no linear association between the QRS-T angle and the various QTc formulas (For QRS-T angle QTcRTH p = 0.76, QTcB p = 0.83, QTcFri p = 0.90, QTcFra p = 0.13, QTcH p = 0.97; For square root transformation of the QRS-T angle QTcRTH p = 0.18, QTcB p = 0.33, QTcFri p = 0.95, QTcFra p = 0.47, QTcH p = 0.33). Agreement between machine and manual QT measurements was low. CONCLUSIONS: The frontal QRS-T angle cannot substitute the QTc in assessing the blockage of cardiac potassium channels in drug induced long QT syndrome. We also support the consensus that despite the availability of machine measurements of the QT interval, manual measurements should also be performed.