Cardiac Magnetic Resonance for Lesion Assessment in the Electrophysiology Laboratory.

Cardiac magnetic resonance imaging (CMR) is of growing importance in cardiac electrophysiology (EP). This imaging modality is clinically used for the diagnosis of arrhythmogenic substrates, prognosis of sudden cardiac death, pre-procedural planning, and procedural image integration. Because of the increasing utility of CMR in the EP environment, interest in the use of real-time CMR for EP procedural guidance has amplified in recent years. This is an attractive option for many reasons. Currently, there is considerable radiation exposure to both patients and providers during EP procedures and CMR offers a welcome radiation-free alternative to fluoroscopy. The other fundamental advantage of CMR over other imaging techniques is enhanced visualization of soft tissue structures with excellent spatial and temporal resolution. The enhanced soft tissue resolution with CMR promises not only to enhance the identification of arrhythmogenic substrates during the procedure, but also to augment lesion assessment to distinguish acute edema in the setting of an ablation from the chronic lesion that ultimately results. This distinction may be critical, because a significant proportion of long-term arrhythmia recurrences following acutely successful pulmonary vein isolation or other substrate or trigger ablations are likely attributable to resolution of acute edema that does not persist as a chronic lesion. These advantages present the exciting possibility of real-time CMR guided ablation procedures, in which imaging assists both the identification of ablation targets and the evaluation of a successful ablation. Nevertheless, several limitations persist in the development of a real-time CMR guided ablation system. Ongoing academic and industry endeavors are beginning to overcome the significant electromagnetic interference and safety issues. However, the use of CMR for real-time characterization of ablation lesions has also been challenged by the delayed nature of lesion formation. Multiple CMR imaging techniques are possible, including T2-weighted sequences to evaluate edema, as well as T1-weighted sequences to evaluate scar formation using the native T1 characteristics or late gadolinium enhancement (LGE). Each of these methodologies offers advantages as well as disadvantages. Therefore, studies that characterize the diagnostic accuracy of each sequence in different tissues, and depending upon the modality of ablation, and timing of image acquisition after ablation are timely.