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

Abstract

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 À0.2 § 41.6 ms (before AF vs AF) and À6.6 § 35.4 ms (after AF vs AF), respectively. QTc corrected by the Bazett formula (before AF vs AF À38.7 § 52.3 ms; after AF vs AF À42.6 § 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.

Atrial fibrillation and QT corrected. What is the best formula to use?

“…This result is in full agreement with the results of previous authors, who demonstrated that the Bazett's formula produced the longest corrected QT in AF compared with other formulas, 4 that is an overestimation of the QTc during AF, 6 the most HR dependent 18,21,22 …”

“…This result is in full agreement with the results of previous authors, who demonstrated that the Bazett's formula produced the longest corrected QT in AF compared with other formulas, 4 that is an overestimation of the QTc during AF, 6 the most HR dependent. 18,21,22 The most important clinical implication of this overestimation of the QTc during AF may be the choice of antiarrhythmic or anticancer drugs. Some patients are at risk of being undertreated with even vital medications for this overestimation of the QTc.…”

“…The idea that the QT depends on the HR is commonly recognized, but QT/RR hysteresis, which states that the QT does not adapt immediately when the HR changes, is less well understood [22,[24][25]. To put it more simply, measuring the QT in the first subsequent RR will result in a longer corrected QTc if the frequency increases suddenly.…”

Case report: A 56-year-old woman presenting with torsades de pointes and cardiac arrest associated with levosimendan administration and underlying congenital long QT syndrome type 1

“…The tangent method was used to define the end of the T-wave in the lead with the longest QT interval. All measured QT intervals were corrected for cardiac frequency using Fridericia's formula [ 10 , 11 ]. Prolongation of the QT interval was defined as a QTc interval ≥460 ms in females [ 12 ].…”

QTc interval measurement in patients with right bundle branch block: A practical method

“…QT should be corrected based on R‐R interval to eliminate heart rate effects on QT interval (Yu et al, 2022). Bazett (1997) created a formula for corrected QT (QTc) calculation approximately one century ago.…”