How to correct QT interval after cardiac resynchronisation therapy

This study evaluates various formulae used to correct the QT interval in patients with wide QRS complexes to calculate corrected QT (QTc) following Cardiac Resynchronisation Therapy (CRT).

We included patients with severe heart failure and left bundle branch block, presenting with a QRS duration of at least 120 milliseconds, who underwent successful CRT implantation. Patients were excluded if they had non-lateral left ventricular lead placement, metabolic disorders, atrial fibrillation, atrial tachycardia, or high-degree atrioventricular block prior to implantation. QT intervals were measured pre- and post-implantation and corrected for QRS duration and heart rate using the Boggosian, Wand, Rautaharju, Yankelson, Tang & Rabkin, Bazett, Framingham, Hodges and Fredericia formulae.

A total of 51 patients met the study criteria. After CRT, the QRS duration significantly decreased from 189.68 ± 18.06 milliseconds to 165.25 ± 18.78 milliseconds. However, the QT interval corrected using Bazett's formula showed no significant change (522.30 ± 33.37 milliseconds versus 524.06 ± 36.52 milliseconds). Among the various correction methods, the combination of the Bogossian formula (for QRS duration) followed by the Hodges formula (for heart rate), or the Rautaharju formula followed by the Fredericia formula, produced comparable QT intervals. Similarly, correcting heart rate with the Fredericia formula followed by QRS correction with the Rautaharju formula yielded consistent results.

Our findings indicate that different formulae for correcting QT intervals for heart rate and QRS duration may yield varying results. Notably, the use of the Bogossian formula followed by the Hodges formula, or the combination of the Rautaharju and Fredericia formulae, produces relatively consistent QT intervals before and after CRT. Further research is needed to validate these findings.