2012 Theses Doctoral

Electromechanical Wave Imaging

Provost, Jean

Cardiac conduction abnormalities and arrhythmias are associated with stroke, heart failure, and sudden cardiac death, and remain a major cause of death and disability. However, the imaging tools currently available to the physician to guide these treatments by mapping the activation sequence of the heart are invasive, ionizing, time-consuming, and costly.

In this dissertation, Electromechanical Wave Imaging (EWI) is described with an aim to characterize normal and abnormal rhythms noninvasively, transmurally, at the point of care, and in real time. More specifically, the methods to map the electromechanical wave (EW), i.e., the transient deformations occurring in response to the electrical activation of the heart, are developed and optimized. The correlation between EW and the electrical activation sequence during both normal and abnormal rhythms is demonstrated in canines in vivo and in silico. Finally, EWI is shown to noninvasively detect and characterize arrhythmias and conduction disorders in humans.

Novel ultrasound imaging methodologies were developed to track the EW. Radio-frequency (RF) frames acquired at high frame rates were used in conjunction with cross-correlation algorithms to map the onset of the small, localized, transient deformations resulting from the electrical activation and forming the EW. To validate the capability of the EW to characterize cardiac rhythm, it was compared against the electrical activation in vivo and in silico. A high correlation between the electrical and electromechanical activations was obtained in normal canines in vivo during various pacing schemes and sinus rhythm. An in vivo-in silico framework was also developed to demonstrate that this correlation is maintained transmurally and independently of the imaging angle. EWI was also validated in abnormal canine hearts in vivo during ischemia, left bundle branch block, or atrio-ventricular dissociation.

In a clinical feasibility study, we demonstrated that EWI was capable of noninvasively mapping normal and abnormal activation patterns in all four cardiac chambers of human subjects using a readily available clinical ultrasound scanner. Specifically, EWI maps were generated for three heart failure patients with cardiac resynchronization therapy (CRT) devices and for three patients with atrial flutter who subsequently underwent catheter mapping and radiofrequency ablation. Preliminary validation of EWI maps against invasive transcutaneous electroanatomical cardiac mapping was also demonstrated.

EWI has the potential of becoming a noninvasive and highly translational technology that can serve as a unique imaging tool for the early detection, diagnosis and treatment monitoring and follow-up of arrhythmias and conduction disorders through ultrasound-based mapping of the transmural electromechanical activation sequence reliably, at the point of care, and in real time.