Abstract 14608: QRS Voltage in Lead V1 After Cardiac Resynchronization Predicts Survival in Patients With Left Bundle Branch Block

Abstract

Introduction: The QRS complex on the electrocardiogram is a reflection of the summation of instantaneous electrical forces within the heart. In left bundle branch block (LBBB), the propagation of the electrical wavefront is dyssynchronous and unopposed and is thereby associated with an increase in the QRS voltage in precordial leads like lead V1, which are closer to perpendicular to the direction of propagation. Hypothesis: The aim of this study was to assess the impact of cardiac resynchronization therapy (CRT) on QRS morphology and voltage in lead V1, and its ability to predict response. Methods: The study included 103 consecutive patients with LBBB (age 69±12 years, 80 men, left ventricular ejection fraction 22±6%, QRS width 159±22ms), who received CRT for a median duration of 42 months (IQR 28-53 months). Results: During follow-up 18 patients died. Total QRS amplitude in lead V1 decreased significantly from 1.4±0.9mV at baseline to 0.8±0.5mV post CRT, (P value = 0.0002), the decrease being more pronounced in patients who survived when compared to nonsurvivors (0.8±0.9mV vs. 0.3±0.9mV P value= 0.021). The algebric sum of the positive and negative deflections of the QRS complex in V1 (sumQRS V1 ) changed significantly from -1.4±0.7mV at baseline to -0.05±0.7mV post CRT (p value <0.0001). Patients who survived had a more negative sumQRS V1 post CRT than nonsurvivors (-0.2±0.6mV vs +0.4±0.5mV p value=0.0012), and the sumQRS V1 cutoff that best separated survivors from non-survivors was +0.3mV. Patients with sumQRS V1 < 0.3mV had a significantly better survival than patients with sumQRS V1 ≥0.3mV (Figure). A >50% decrease in QRS amplitude in V1 with CRT, and sumQRS V1 post CRT <0.3mV independently predicted event free survival in a multivariate Cox regression model that included age, gender, baseline left ventricular ejection fraction and the change in QRS duration. Conclusions: Changes in QRS voltage in lead V1 after CRT predict survival in patients with LBBB.