MR-Guided Assessment and Management of Ventricular Tachycardia

This thesis describes the electrical and physiological characterization of cardiac tissue with myocardial infarction (MI) responsible for abnormal cardiac rhythms such as ventricular tachycardia (VT), using a newly-developed magnetic resonance imaging (MRI) electrophysiology system. In electrophysiology (EP), radiofrequency (RF) catheter ablation combined with cardioverter-defibrillator implantation is a first-line action to manage ventricular VT. Unfortunately, this therapy is known to have sub-optimal success rates in a large number of patients because of difficulties to accurately identifying the arrhythmic target regions. Currently, characterization of post-MI scars is performed by using catheters to measure electrical signals of the endocardial tissue (electroanatomical mapping), under x-ray fluoroscopy guidance. Prolonged radiation exposure to both the cardiologist and the patient have made the use of MRI extremely attractive; further, unlike x-ray imaging, MRI provides post-MI scars with direct visualization, characterization in three dimensions and the ability to visualize ablation lesions. Although recent research has focused on registration between pre-acquired MR images and electroanatomical maps, a potentially more useful approach is to use real-time MRI to directly locate and characterize potential arrhythmogenic regions during the EP procedure. A real-time MR-guided EP system was developed and validated to perform EP diagnostic procedures, such as mapping and pacing. In a series of animal studies, the system demonstrated the ability to use active catheter tracking and intra-procedural MR imaging to navigate to specific regions in the left ventricle and record intracardiac electrical signals. A study correlating myocardial fibrotic scar detected by multicontrast late enhancement (MCLE) MRI and electroanatomical voltage mapping demonstrated that MRI information (transmurality, tissue classification, and relaxation rate) can accurately predict areas of myocardial fibrosis identified with bipolar voltage mapping. Finally, MCLE-derived gray zone was shown to have a high correspondence to regions with a high proportion of abnormal intracardiac signals. The methods described in this thesis help advance the understanding of infarcted tissue responsible for ventricular tachycardia. Further studies are proposed to perform RF ablation lesions and correlate pre- and post-ablation tissue electrophysiological properties with MRI.Ph