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

AIMS: 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 AND

RESULTS

Twenty 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. Five patients were additionally scanned after changing the LV lead pacing pole. A custom-made 2D-HFR-STE algorithm tracked the cardiac wall in the three 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. For most HV, activation started from mid-anteroseptum, at 23 ± 5 ms, spreading basal-inferolaterally at 50 ± 8 ms. During BiV off, the average septal activation was 36 ± 2 ms; the average lateral was 81 ± 21 ms (P < 0.01). During BiV on, the respective times were 53 ± 6 ms and 52 ± 6 ms (P = 0.3). Altering the LV lead pacing pole changed the lateral wall activation onset accordingly.

CONCLUSION

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.