A New Electromechanical Wave Imaging Dispersion Metric for the Characterization of Ventricular Activation in Different Cardiac Resynchronization Therapy Pacing Schemes

Abstract

Conventional biventricular (BiV) pacing cardiac resynchronization therapy (CRT) is an established treatment for heart failure patients. Recently, multiple novel CRT delivering technologies such as His-Bundle pacing have been investigated as alternative pacing strategies for optimal treatment benefit. Electromechanical Wave Imaging (EWI), a high frame-rate echocardiography-based modality, is capable of visualizing the change from dyssynchronous activation to resynchronized BiV-paced ventricles in 3D. This proof-of-concept study introduces a new EWI-based dispersion metric to further characterize ventricular activation. Patients with His-Bundle device implantation (n = 4), left-bundle branch block (n = 10), right-ventricular (RV) pacing (n = 10), or BiV pacing (n = 15) were imaged, as well as four volunteers in normal sinus rhythm (NSR). EWI successfully mapped the ventricular activation resulting from His-Bundle pacing. Additionally, very similar activation patterns were obtained in the NSR subjects, confirming recovery of physiological activation with His pacing. The dispersion metric was the most sensitive EWI-based metric that identified His pacing as the most efficient treatment (lowest activation time spread), followed by BiV and RV pacing. More specifically, the dispersion metric significantly (p < 0.005) distinguished His pacing from the other two pacing schemes as well as LBBB. The initial findings presented herein indicate that EWI and its new dispersion metric may provide a useful resynchronization evaluation clinical tool in CRT patients under both novel His-Bundle pacing and more conventional BiV pacing strategies.

Fig. 1.

Electromechanical Wave Imaging workflow. This figure illustrates the entire EWI processing pipeline on the cardiac ventricles of a 69-year old male CRT patient in conventional biventricular pacing.

Fig. 2.

3D-rendered ventricular isochrones on a) an 87-year-old male with His-Bundle pacing and b) a 26-year-old healthy male volunteer in normal sinus rhythm (NSR). LWAT = mean LV lateral wall activation time, RWAT = mean RV free wall activation time.

Fig. 3.

Histograms of the activation time distributions and associated dispersion values for an atrial flutter patient under His-Bundle pacing, an LBBB case, a conventional BiV pacing CRT, a chronic RV apex pacing patient and a healthy volunteer in NSR. In the His Bundle pacing case, the ventricular activation time distribution may have been impacted by the underlying atrial arrhythmia, contrary to the four other subjects who all had sinus rhythm present at baseline with 1:1 AV synchrony. Std = standard deviation, NSR = normal sinus rhythm, AV = atrioventricular.

Fig. 4.

Dispersion of the activation time distributions across the different rhythms and pacing conditions. One-way ANOVA followed by post-hoc analysis with Tukey’s multiple comparisons. All tested pairs and associated p-values are listed in the table on the right of the plot. Significance was achieved for all pair-wise comparisons, except for the two following: i) NSR vs His pacing; and ii) BiV vs RV pacing (despite BiV performing slightly better than RV overall with shorter dispersion values). N.S. = non-significant.