Widely used Bazett formula overestimates corrected QT interval during an AF attack

An atrial fibrillation (AF) attack does not substantially impact the corrected QT interval (QTc), a recent study suggests. Of existing formulae to correct QT, the Framingham formula achieves the best results while the Bazett formula appears to overestimate QTc during an AF attack.

The researchers enrolled 101 patients (mean age 69.0 years, 55.4 percent men) with paroxysmal AF as determined by a 24-hour Holter monitoring test. Aside from the Bazett and Framingham equations, four other formulae for correcting QT to heart rate were assessed: Fridericia, Hodges, Dmitrienko, and Rautaharju.

Almost all formulae tested showed that the QTc interval during an AF attack was significantly shorter than that before and after AF episodes. The only exception was the Framingham formula, which showed that QTc intervals did not significantly differ before, during, and after an AF episode (p=0.335).

Notably, at every time point, the Bazett formula consistently yielded the longest QTc interval value as compared with all other formulae tested. On the other hand, the Framingham formula provided the shortest QTc interval during an AF attack, while the Dmitrienko formula did so before and after AF.

Bland-Altman analysis were then used to assess the performance of each formula for correcting QT. The Framingham formula performed excellent homogeneity across all time points, with a mean delta difference of –0.2 and –6.6 ms before vs during and during vs after an AF episode, respectively.

In contrast, heterogeneity of QT correction was significant for both the Bazett and Dmitrienko formulae.

“The most commonly used Bazett formula significantly overestimated the QTc interval during AF, and its accuracy in correcting the QT interval was highly dependent on the HR,” the researchers said.