Magnetic resonance imaging in clinical cardiac electrophysiology

Radiofrequency ablation is routinely used to treat numerous cardiac arrhythmias originating in the atrium and the ventricle. The process of ablation was pioneered to treat supraventricular tachycardias originating from fixed electrical circuits. These circuits could be identified using innovative electrophysiological maneuvers, which have been refined over the years to achieve excellent cure rates using fluoroscopy. More recently, electrophysiology ablation procedures have been greatly expanded to treat more diffuse arrhythmias like atrial fibrillation and ventricular tachycardia that are sustained by a remodeled myocardium or scar tissue. Given that there is no fixed circuit to target during most of these ablations, especially atrial fibrillation, there is a need to better visualize the substrate or the remodeling in the myocardium. Currently, when ablating atrial fibrillation or ventricular tachycardias, it is routine to use a cardiac CT or intra-cardiac echocardiogram to provide a three-dimensional anatomical structural map of the heart. This approach does not provide any substrate information like fibrosis or scar tissue in the myocardium. MRI has excellent soft-tissue visualization characteristics and has been used extensively to characterize the myocardial tissue as scar or fibrosis. This structural remodeling information of the myocardium is increasingly being used, along with the three-dimensional structural information in the ablation procedures, with the goal of improving the outcome. In addition MRI can also be used to visualize radiofrequency ablation lesions, potentially leading to significant improvement in procedural outcomes.