Color-coded speckle tracking radial strain dyssynchrony analysis in a canine model of left bundle branch block and cardiac resynchronization therapy

Introduction

Quantification of left ventricular (LV) dyssynchrony is important for heart failure patients with left bundle branch block to assess the effectiveness of cardiac resynchronization therapy (CRT). We tested the hypothesis that LV contraction dyssynchrony and the impact of CRT on restoration of efficient synchronous contraction could be quantified from discordant regional radial strain.

Methods

Seven open-chest dogs had grayscale mid-LV short axis echo images. Right atrial (RA) and right ventricular (RV) to simulate left bundle branch block, and LV free wall (LVf) and apical LV (LVa) pacing leads were placed to create CRT. Regional radial strain was analyzed by custom software (Toshiba Corp.) for color-coded speckle tracking in six radial sites during four different pacing modes: RA, RA–RV, RA–RV–LVf (CRTf) and RA–RV–LVa (CRTa). Dyssynchrony was assessed as the maximum time difference between the earliest and latest time to peak segmental strain. RA pacing was used as minimal dyssynchrony and RA–RV pacing as maximal dyssynchrony. For each pacing mode, the global efficient strain was calculated as the area under the curve (AUC) of the global positive strain. During RA–RV we calculated the global negative strain as the sum of AUCs of negative individual segment strains.

Results

Baseline dyssynchrony during RA pacing control was minimal (58 ± 40 ms). RV pacing increased dyssynchrony (213 ± 67 ms, P < 0.05 vs control) and reduced LV stroke work (89 ± 46 mJ, P < 0.05 vs RA). Radial dyssynchrony was improved by both CRTf and CRTa (116 ± 47 ms, 50 ± 34 ms, respectively, P < 0.05 vs RV). RV pacing displayed early septal wall thickening and opposing wall thinning with a lower efficient strain compared with RA (257 ± 124%/ms vs 129 ± 80%/ms, P < 0.05), whereas both CRTf and CRTa restored efficient strain to RA pacing levels (205 ± 78%/ms and 223 ± 76%/ms). During RA–RV, the global efficient strain and negative global strain were similar (230 ± 88%/ms vs 257 ± 123%/ms, P < 0.05) and correlated (r² = 0.96) with RA global efficient strain.

Conclusion

LV contraction efficiency and cardiac performance can be quantified by speckle tracking radial strain analysis. RA–RV-induced decreased efficiency and improved efficiency with both CRTa and CRTf can be characterized by summed regional strain changes.