High frame rate speckle tracking echocardiography to image the left ventricular mechanical activation sequence in healthy participants and patients with left bundle branch block

Abstract Objective Electrical activation mapping is essential for identifying ablation targets in the treatment of cardiac arrhythmias. This study investigates high-frame-rate (HFR) speckle-tracking echocardiography (STE) as a non-invasive alternative to conventional electrophysiologic studies for constructing mechanical activation maps and defining left ventricular (LV) activation onset. Methods 20 healthy volunteers (HV) and 25 patients with a biventricular pacemaker (BiV) underwent HFR ultrasound scanning. Patients were scanned during BiV on and off, hence reintroducing native activation - left bundle branch block (LBBB) pattern. 5 patients were additionally scanned after changing the LV lead pacing pole. A custom-made 2D-HFR-STE algorithm tracked the cardiac wall in the 3 conventional apical echocardiographic views. Strain rate (SR) curves were computed for each wall segment in a 16-segment LV model to measure the time between electrical and mechanical activation (i.e. time between QRS onset and first positive-to-negative zero-crossing in the SR curve). The timings were displayed in a bull’s-eye plot, representing each subject’s activation map. Results For most HV, activation started from mid-anteroseptum, at 23±5ms, spreading basal-inferolaterally at 50±8ms. During BiV off, the average septal activation was 36±2ms; the average lateral was 81±21ms (p0.01). During BiV on, the respective times were 53±6ms and 52±6ms (p=0.3). Altering the LV lead pacing pole changed the lateral wall activation onset accordingly. Conclusions HFR-STE was able to map normal activation, measure the known septal-to-lateral LBBB dyssynchrony and identify the paced segment in 92% of the cases. HFR-STE could be a promising tool in constructing LV activation maps.