Abstract 2822: Imaging of the Propagation of the Contraction Wave Using RF-Based Speckle Tracking In Vivo

Abstract

OBJECTIVE : Using a combination of high-frequency ultrasonography, ECG gating, and RF-based motion estimation, our laboratory has developed a novel technique for the noninvasive mapping of contraction waves in the intact murine left ventricle. In this study, we sought to measure the velocity and direction of contraction waves in the murine heart during native conduction and pacing. METHODS : Twelve wild-type mice were anesthetized with IP pentobarbital, and an octapolar pacing catheter introduced into the right ventricle (RV) through the external jugular vein. In vivo ultrasound RF frames (30 MHz) were acquired at 8000 fps (Vevo 770, Visualsonics, Inc.), using ECG gating. Axial frame-to-frame motion were estimated using a speckle tracking method. Images were obtained in the parasternal long axis view under three conditions; sinus rhythm (SR), right atrial (RA) pacing, and RV pacing. Contraction was analyzed using ciné-loop images. RESULTS : Distinct contraction patterns were noted during isovolumic contraction (IC) ejection under all conditions. In SR, during IC, convergent motion of the septal wall (SW) and posterior wall (PW) began during the latter half of the QRS at the apex and spread basally, causing divergent movement at the base. At the onset of ejection, medial contraction spread to the base. Similar results were obtained with RA pacing. During RV pacing, the IC phase began with convergent motion of the basal SW and PW that spread apically, causing divergent motion of the apical SW and PW. During ejection, convergent motion of the apical SW and PW developed which spread to the basal SW and PW. This difference between SR/RA pacing and RV pacing was found in all mice (n=12). We found a significantly slower contraction wave velocity during RV pacing (0.5213 +/- 0.3125 m/s) than during SR/RA pacing (0.8496 ± 0.2214 and 0.8379 ± 0.1967 m/s, respectively) (p<0.01), in line with previously reported results. CONCLUSION : This study demonstrates the ability of this modality to noninvasively map the velocity and direction of contraction waves. Using this technique, we demonstrate the difference in motion patterns between native conduction and ventricular pacing. This technique has potential applications in the noninvasive assessment of ventricular dyssynchrony.