Electrocardiographic Imaging: Development of a Non-smooth Regularization Method and Clinical Application in Patients with Wolff-Parkinson-Whote Syndrome and Heart Failure
Date of Award
Doctor of Philosophy (PhD)
Electrocardiographic Imaging (ECGI) is a novel noninvasive imaging modality for cardiac electrophysiology. ECGI involves the inverse problem of computing epicardial potentials from multi-electrode body-surface electrocardiograms. Tikhonov regularization is commonly employed, which imposes penalty on the L2-norm of the potentials (zero-order) or their derivatives. However, L2-norm penalty function can cause considerable smoothing of the solution. We use the L1-norm of the normal derivative of the potential as a penalty function in regularizing inverse solutions of our ECGI problem. L1-norm solutions were compared to zero-order and first-order L2-norm Tikhonov solutions and to measured ‘gold standards’ in previous experiments with isolated canine hearts. Solutions with L1-norm penalty function (average relative error [RE] = 0.36) were more accurate than L2-norm (average RE= 0.62). In addition, the L1-norm method iilocalized epicardial pacing sites with better accuracy (3.8±1.5 mm) compared to L2-norm (9.2±2.6 mm) during pacing in five pediatric patients with congenital heart disease..
ECGI was applied to localize accessory pathway insertion sites in pediatric Wolff-Parkinson-White patients to facilitate their catheter ablation procedure. Patients were also followed up several minutes, 1 week and 1 month post-ablation to determine the changes in epicardial activation and repolarization following return to normal sinus rhythm, and hence study and demonstrate the phenomenon of ‘cardiac memory’ in these patients.
In a separate clinical study, ECGI was applied to a group of non-ischemic heart failure patients undergoing cardiac resynchronization therapy, in conjunction with echocardiographic Tissue Synchronization Imaging, to study the electrophysiological substrate and the relationship between electrical and mechanical components of left ventricular dyssynchrony..
ECGI was also applied to a substantially different population of heart failure patients with congenital heart disease to image the substrate, evaluate intra-ventricular electrical dyssynchrony and identify candidates suitable for cardiac resynchronization therapy. ECGI activation maps were used to identify optimal areas for placement of the resynchronization leads in selected patients.
The above studies contributed to the continued development of methodology of a novel noninvasive cardiac electrophysiologic imaging modality (ECGI) and demonstrated the feasibility of its application for improved diagnosis and evaluation of patients in the clinical setting.
George F Van Hare, Pamela K Woodard, Frank CP Yi,