Comparison of QT/RR Relation Based on a 15-s Averaged ECG and a Single Beat ECG During Atrial Fibrillation

Background: The aim of this study was to compare QT/RR relation based on a 15-s averaged beat ECG with a single beat ECG during atrial fibrillation (AF) and to determine which was better to estimate the QT interval after sinus restoration. Methods and Results: QT and RR intervals were measured using an automatic QT analyzing system in 33 patients who had both AF and sinus rhythm on the same 24-h Holter ECG recording. In 14 patients, antiarrhythmic drugs (AAD) were administered. QT/RR relations were analyzed from ECG waves obtained by the summation of consecutive QRS-T complexes during each 15-s period (QT/RR-average) and a single beat QRS-T (QT/RR-single). During sinus rhythm, the slope of QT/RR-average did not differ from that of QT/RR-single in patients with and without AAD. On the other hand, during AF, the slope of QT/RR-average was significantly greater than that of QT/RR-single (without AAD: 0.12±0.06 vs. 0.06±0.03, P