Cardiac Dyssynchrony Quantitated by Time-to-Peak or Temporal Uniformity of Strain at Longitudinal, Circumferential, and Radial Level: Implications for Resynchronization Therapy

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Abstract

Background

The standard deviation of time to peak strain (TPS-SD) has been proposed as an index of left ventricular (LV) dyssynchrony in patients to be resynchronized. However, TPS-SD is sensitive to noise, and the influence of outliers on TPS-SD is also relevant. Alternatively, dyssynchrony can be indexed by temporal uniformity of strain (TUS), whereby a time plot of regional strains, arranged for LV location, is subjected to Fourier analysis. If segments shorten simultaneously (synchronously), the plot appears as a straight line, with power only in the zero-order Fourier term, whereas regionally clustered dyssynchrony generates an undulating plot with higher power in the first-order term. TUS index reflects zero-order relative to first-order plus zero-order power.

Methods

In this study, TUS and TPS-SD were computed in 68 patients (QRS duration ≥ 120 ms; ejection fraction ≤ 0.35) in whom longitudinal, circumferential, and radial strains were measured using speckle-tracking two-dimensional echocardiography before and 3 to 6 months after cardiac resynchronization therapy (CRT), together with LV volumes.

Results

Following CRT, LV volume decreased (diastolic, −10 ± 20%) and ejection fraction improved from 0.23 +/- 0.07% to 0.30 +/- 0.10% (P < .001 for both). Circumferential strain was ameliorated as well (P = .054). Two-way analysis of variance revealed TUS improvement after CRT (P = .043), with a trend for CRT to contrast asynchrony at the circumferential (+0.06 ± 0.25) and longitudinal (+0.05 ± 0.18) levels compared with the radial level (−0.002 ± 0.18) (interaction P = .06). This was not true for TPS-SD. Multivariate analysis revealed that only TUS, assessed before CRT circumferentially, predicted ejection fraction improvement after CRT. Other asynchrony variables failed in the model.

Conclusion

Dyssynchrony indexed by circumferential TUS yields greater CRT benefits than that indexed by TPS-SD, supporting the idea of targeting TUS-measured dyssynchrony as a more informative quantitative measurement in CRT patients.

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