Electrophysiologic substrate and intraventricular left ventricular dyssynchrony in nonischemic heart failure patients undergoing cardiac resynchronization therapy

Abstract

Background: Electrocardiographic imaging (ECGI) is a method for noninvasive epicardial electrophysiologic mapping. ECGI previously has been used to characterize the electrophysiologic substrate and electrical synchrony in a very heterogeneous group of patients with varying degrees of coronary disease and ischemic cardiomyopathy.

Objective: The purpose of this study was to characterize the left ventricular electrophysiologic substrate and electrical dyssynchrony using ECGI in a homogeneous group of nonischemic cardiomyopathy patients who were previously implanted with a cardiac resynchronization therapy (CRT) device.

Methods: ECGI was performed during different rhythms in 25 patients by programming their devices to biventricular pacing, single-chamber (left ventricular or right ventricular) pacing, and native rhythm. The electrical dyssynchrony index (ED) was computed as the standard deviation of activation times at 500 sites on the LV epicardium.

Results: In all patients, native rhythm activation was characterized by lines of conduction block in a region with steep activation-recovery interval (ARI) gradients between the epicardial aspect of the septum and LV lateral wall. A native QRS duration (QRSd) >130 ms was associated with high ED (≥30 ms), whereas QRSd <130 ms was associated with minimal (25 ms) to large (40 ms) ED. CRT responders had very high dyssynchrony (ED = 35.5 ± 3.9 ms) in native rhythm, which was significantly lowered (ED = 23.2 ± 4.4 ms) during CRT. All four nonresponders in the study did not show significant difference in ED between native and CRT rhythms.

Conclusion: The electrophysiologic substrate in nonischemic cardiomyopathy is consistent among all patients, with steep ARI gradients co-localizing with conduction block lines between the epicardial aspect of the septum and the LV lateral wall. QRSd wider than 130 ms is indicative of substantial LV electrical dyssynchrony; however, among patients with QRSd <130 ms, LV dyssynchrony may vary widely.

Conflict of interest statement

Conflict of Interest Disclosures: Y. Rudy co-chairs the scientific advisory board and holds equity in CardioInsight Technologies (CIT). CIT does not support any research conducted by Y.R., including that presented here.

Copyright © 2011 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1

ECGI activation-isochrone maps in patient # 2, who had a wide QRS (QRS duration QRSd=215 ms) pre-implant and responded well to CRT. Isochronal lines are depicted in black. Thick black lines indicate conduction block, while crowded isochronal lines indicate slow conduction. Pacing sites are indicated by asterisk. Each panel shows anterior (left,ANT) and inferior (right, INF) four-chamber views. Epicardial activation sequences are imaged during 1) optimal CRT settings (CRT-OPT) 2) nominal CRT settings (CRT-NOM) 3) LV pacing (LV-P) 4) RV pacing (RV-P) and 5) native sinus rhythm (NAT). QRS duration (QRSd) and electrical dysynchrony index (ED) computed from the epicardial activation maps (in milliseconds) are shown for each rhythm. RA- right atrium, LA- left atrium. The septal aspect of the epicardium is shown by dotted lines (purple, ANT view and grey, INF view) in the NAT panel.

Figure 2

Native rhythm activation and ARI maps from three patients, displayed together to demonstrate the co-localization of conduction block lines (thick black lines on activation map) and areas of steep repolarization gradients (white arrows on ARI maps).

Figure 3

Total repolarization time (RT) maps during native rhythm in three patients whose ARI maps are shown in Figure 2 (in identical views).

Figure 4

Top: ARI maps in patient #12 who had a narrow QRS duration (100 ms). White arrows indicate ARI dispersion in the LV between the epicardial aspect of the septum and lateral wall. Bottom: RT maps in the same patient.

Figure 5

ECGI activation-isochrone maps in patient #12 who had a normal QRS duration and left bundle branch block pattern before implant, arranged in the same format as Figure 1. Note the large electrical dysynchrony (ED=32 ms) in the native rhythm (NAT) in spite of a normal QRS duration (QRSd=100 ms). CRT (CRT panel) restores electrical synchrony (ED=20 ms) in the normal range.

Figure 6

ECGI activation-isochrones in a non-responder patient (#8), arranged in the same format as Figure 1. Note that in spite of a wide QRS duration (QRSd>120 ms) in the native rhythm (NAT), electrical dyssynchrony of epicardial activation was minimal (ED=25 ms) because only a small portion of the LV lateral wall activated late (light blue). Electrical dyssynchrony index remained unchanged with CRT (CRT panel).

Figure 7

Baseline CRT and native activation in another non-responder patient (#22). Native activation shows earliest activation of LV (red) 20 ms before earliest RV activation (light green) and electrical dyssynchrony (ED) close to normal value (24 ms). CRT pacing did not improve ED (29 ms).

Figure 8

Scatter plots of electrical dyssynchrony (ED) vs QRS duration (QRSd), 1) CRT rhythm 2) LV paced rhythm (LV-P) 3) RV paced rhythm (RV-P) and 4) native sinus rhythm (NAT).