QT correction in atrial fibrillation – Measurement revisited

QT interval measured in the electrocardiogram (ECG) varies with RR interval challenging the calculation of corrected QT (QTc) in Atrial fibrillation (AF). To identify the ideal Lead, number of complexes and the formula to measure QTc that correlates best between AF and sinus rhythm (SR). We identified ECGs from patients with AF before and after conversion to SR. After excluding patients on drugs and clinical conditions that prolong QT interval, QTc was calculated from all the leads using the formulae: Bazett (BF), Fridericia (FF), Framingham(FrF), Hodges (HF), Saige (SF) and Rautaharju (RF) during AF and SR. After identifying the lead with best linear correlation, we calculated QTc following the longest RR, multiple QRS complexes and average automated RR interval during AF and compared to SR. In 52 patients (male 69%, age 63 ± 9 yrs), QTc measured from Lead II correlated best with SR in majority of the formulae. QTc was consistently shorter with linear formulae. While BF overestimated QTc, FF was optimal comparing AF vs SR (416 ± 33 vs 411 ± 38 ms, ns) calculated from single, multiple or average automated RR interval. Bland Altman analysis of the average automated QTc versus the delta of individual automated QTcs shows the least variation in the QTc calculated by FF. BF in commercial software is not ideal for measurement of QTc in AF, Fridericia Formula in lead II from the average RR from automated ECG measurement maybe utilized for the calculation of QTc.