Recoordination of opposing walls drives the response to cardiac resynchronization therapy: a longitudinal study using a strain discoordination index

Abstract

Background and aims: Intraventricular dyssynchrony has traditionally been studied by means of contraction delays between different myocardial segments. Recently, the discoordination of opposing wall contraction throughout the cardiac cycle has been proposed as a more faithful predictor of response. Aim of the current study was to evaluate which parameters - mechanical dyssynchrony or discoordination - normalize with left ventricular response to cardiac resynchronization therapy (CRT).

Methods: Cardiac mechanics were analysed before and after 6 months of CRT in 53 patients with left bundle branch block and advanced heart failure. Discoordination was quantified by means of the transverse strain discoordination index (TSDI) at basal and mid-ventricular segments; this index takes into account the percentage of time in the cardiac cycle in which cardiac deformation (transverse strain) of the two opposing walls occurs in noncoordinated directions. Dyssynchrony indices included septal to lateral peak-to-peak transverse strain delay and the standard deviation of time to peak tissue velocity in 12 mid-basal segments (Yu index).

Results: Around 63% of patients met the response criteria. Several baseline indices were predictive of reverse remodelling; TSDI at the mid-ventricular level demonstrated the best accuracy. Time from Q to peak velocity and strain tended to increase in all explored myocardial segments; despite a trend towards a decrease in septal-to-lateral strain delay, the latter decreased equally in responders and in nonresponding patients. Yu index decreased in responders more than in nonresponders, with borderline significance. Basal and medium TSDI remained unchanged in nonresponders and consistently normalized in patients who responded to CRT. The changes in TSDI were significantly correlated with improvements in left ventricular end-systolic volume and ejection fraction; the strongest correlation was observed for changes in TSDI measured at the mid-ventricular level.

Conclusion: Left ventricular reverse remodelling after CRT is accompanied by the recoordination of opposite-wall contraction, as testified by changes in mid-ventricular TSDI, which also reveals as a very good predictor of response. On the contrary, changes of segmental peak-to-peak delays (dyssynchrony indices) fail to capture the complex nature of left ventricular response to CRT.