The ECG in cardiac resynchronization therapy: influence of left and right ventricular preactivation and relation to acute response.

INTRODUCTION: The aims of this study were to compare ECG signs of biventricular electrical resynchronization during cardiac resynchronization therapy (CRT) with various interventricular (VV) delays and to correlate these and other ECG characteristics with the acute hemodynamic benefit of CRT.

METHODS AND RESULTS: Thirty-four patients with heart failure and a left bundle branch block (LBBB) pattern were prospectively enrolled. A 12-lead surface ECG and the relative improvement in left ventricular (LV) dP/dt(max) (the maximum rate of pressure rise) were recorded at baseline and during CRT with VV delays varying from 80 ms LV preactivation to 40 ms right ventricular (RV) preactivation. Rightward QRS-axis shift occurred in 71-80% among all VV delays. Activation reversal to dominant negative in leads I/aVL was progressively observed at increasing LV preactivation (53-65%) and less (18-22%) during RV preactivation. Activation reversal to dominant positive in leads V1/V2 was observed in 21-27% during LV preactivation and in 6-15% during RV preactivation. Higher acute response to CRT was independently predicted by a complete LBBB at baseline (regression coefficient B = 7.7 [0.3-15.0], P = 0.042), later timing of LV depolarization within the QRS at baseline (Q-LVsense: B = 0.2 [0.1-0.3], P = 0.002), and biventricular electrical resynchronization during CRT as evidenced by activation reversal in leads I/aVL (B = 9.9 [3.2-16.6], P = 0.005).

CONCLUSION: ECG signs of biventricular electrical resynchronization are present over a wide range of LV preactivated VV delays but to a lesser extent during RV preactivation. The presence of complete LBBB and longer Q-LVsense at baseline and signs of biventricular electrical resynchronization during CRT predict higher acute hemodynamic response.