Impact of Heart Rate and Rhythm on Corrected QT Interval During Paroxysmal Atrial Fibrillation.

Current knowledge on the dynamic changes of corrected QT (QTc) before, during, and after an atrial fibrillation (AF) episode is limited. It remains controversial which of the presently available formulas performs the best in calculating QTc during AF. This study was designed to explore whether an AF attack would affect QTc and to determine the performance of 6 available formulas in correcting QT before, during, and after AF. A total of 101 patients with Holter-documented paroxysmal AF were enrolled. QT interval before, during, and after AF was measured and corrected to heart rate (HR) by using Bazett, Fridericia, Framingham, Hodges, Dmitrienko, and RTHa formulas. In 40 patients, QTc under AF was compared with under sinus rhythm (SR) with identical HR. Although QT was significantly longer before AF and after AF compared with during AF; there was no difference in QTc between SR and AF with identical HR regardless of the formulas used. QTc calculated by the Framingham formula showed excellent homogeneity with a mean delta difference of -0.2 ± 41.6 ms (before AF vs AF) and -6.6 ± 35.4 ms (after AF vs AF), respectively. QTc corrected by the Bazett formula (before AF vs AF -38.7 ± 52.3 ms; after AF vs AF -42.6 ± 46.9 ms) yielded significant heterogeneity among the 3 time points. In conclusion, AF does not influence QTc. The Framingham formula accurately corrects QT without being affected by the AF episode. The Bazett formula significantly overestimated QTc during AF.