Tuesday, May 20, 2008

Improved QT Correction Method for use in Atrial Fibrillation


Conventional QT corrections may be inappropriate in atrial fibrillation (AF) due to RR variability and QT lag. Existing formulas have been modified by the formula 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.

Materials and Methods

A total of 3063 RR/QT pairs from 28 patients with AF were measured, 22 of whom also had measurements during sinus rhythm. QTc (the Bazett equation), QTLC (the Framingham linear correction), and QTAF were calculated utilizing RRmod, and the rate-independence of each formula in AF tested. Mean QTAF values in AF were compared to QT intervals corrected with QTLC in normal sinus rhythm.


∆QTc/∆RRmod and ∆QTLC/∆RRmod slopes were significantly non-zero whereas ∆QTAF/∆RRmod was not. QTLC and QTc corrections were imperfect at extremes of RRmod while QTAF was constant. QTAF corrections in AF were shorter than QTc or QTLC corrections in NSR.


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