A proposal for a novel formula for measurement of corrected QT interval in patients undergoing left bundle branch area pacing

Background: The QT prolongation is associated with malignant ventricular arrhythmias. However, it is difficult to evaluate QT interval in specific conditions, like in ventricular paced rhythm. The data is scarce about optimal methodology of QT interval measurement in these patients. Herein, we proposed a novel formula for measurement of QT interval in patients with pacemaker implantation via left bundle branch area pacing (LBBaP).

Methods: This is a single-center, retrospective preliminary study (n=63). All patients underwent pacemaker implantation via LBBaP. Electrocardiographic (ECG) parameters [QRS duration (QRSd), QTc (Bazett, Fridericia, Framingham, Hodges, Rautuharju, Spline), Ventricular rate, JT interval] were measured and analyzed before and after the procedure.
Results: The mean age of the study population was 68±13 years, and n=39 (62%) of the patients were female. The mean left ventricular ejection fraction (LVEF) of the patients was 57.9%±4.78. The mean QT interval of the patients was 437.73 ± 55 msec at baseline and 427.17 ± 38.79 msec after the procedure. It was observed that the QTc interval was prolonged in all formulations after the LBBaP procedure. In the analysis of corrected QT (QTc) intervals before and after the procedure, the Hodges formula revealed a closer measurement to the baseline QTc interval. As a result of our analysis, we proposed a novel formula for patients undergoing LBBaP and in paced rhythm: QTc(Dogan)=QTc(H)X0.97=[QT + 1.75 (HR − 60)]x0.97.
Conclusion: There is no clear formula yet for measuring QTc interval in patients with ventricular paced rhythm. In patients with conventional pacemaker implantation, the QT interval has long been calculated by subtracting 50 msec from the QT interval in ventricular paced rhythm. However, the LBBaP is a physiological method compared to conventional pacemaker implantation and its application will increase in future. Thus, a novel formula for proper QT interval measurement is required in those patients with LBBaP.