Conventional QT corrections may be inappropriate in AF due to RR variability and

QT lag. Existing formulas have been modified by RRmod to account for this lag. We

developed a novel correction formula for use in AF (QTAF) based on the slope

∆QT/∆RRmod and report its performance in AF. We also compare QTAF obtained in AF with

rate-independent corrections in NSR.

A total of 3063 RR/QT pairs from 28 patients with AF were measured, 22 of whom also had measurements during sinus rhythm. QT_c, QT_LC, and QT_AF were calculated utilizing RR_mod, and the rate-independence of each formula in AF tested. Mean QT_AF values in AF were compared to QT intervals corrected with QT_LC in NSR.

∆QT_c/∆RR_mod and ∆QT_LC/∆RR_mod slopes were significantly non-zero whereas ∆QT_AF/∆RR_mod was not. QT_LC and QT_c corrections were imperfect at extremes of RR_mod while QT_AF was constant. QT_AF corrections in AF were shorter than QT_c or QT_LC corrections in NSR.

QT_AF is a novel QT correction with a defined relationship to correction in NSR that performs better than existing strategies.