Is There a Future Role for MRI to Guide Mapping and Ablation of Arrhythmias?
Disclosure: See AHA web site. None relevant to this review.
Pub Date: Tuesday, July 8, 2008
Author: Kenneth Ellenbogen, MD, FAHA
Catheter ablation of cardiac arrhythmias currently subjects the patient and the physician performing the procedure to a significant amount of radiation. New techniques, including intravascular ultrasound, robotic catheter movement, and integration of images from magnetic resonance imaging (MRI) scans to help reconstruct cardiac anatomy, may decrease radiation exposure for the patient, physician, or both. MRI has the potential to provide sufficient anatomic detail to define cardiac anatomy, allow tissue and lesion visualization, and potentially allow for performance of mapping and ablation procedures without radiation exposure. However, limitations to the implementation of MRI for this purpose include catheter heating and myocardial necrosis, image distortion, and interference with catheter recording and pacing. The purpose of this study is to determine the feasibility of real-time MRI-guided electrophysiology procedures.
Summary of Study
In the first part of this two-part study, 10 dogs were subjected to electrophysiology studies, which included standard placement of catheters using a 1.5 Tesla MRI system. A variety of technical innovations were necessary to make sure that all components necessary for the electrophysiology study were MRI compatible. Electrophysiology catheters that were passively tracked were constructed with a plastic or woven Dacron body, copper wires, and platinum electrodes. Active tracking catheters also included a 64-MHz loop antenna. Shielding and filtering were developed for the catheters, recording system, and stimulator and consisted of multiple filters. Electrophysiology studies were performed, including pacing and recording from the right atrium and right ventricle. Postprocedure evaluation showed no evidence of thermal injury to the myocardium. Catheter positioning was tested with both passive and active tracking modes. Passive tracking consists of visualization of the catheter components, while active tracking relies on receiving a signal from the catheter for localization. Passive catheter tracking often took several minutes because it required on average a median of five initial real-time imaging planes compared to a median of only two imaging planes with the active tracking mode. Pacing of the atrium or ventricle only occurred during current delivery, and electrogram recording was adequate. No failure to capture was noted during pacing, indicating persistent catheter-tissue contact.
The second part of the study involved placement of a catheter in two patients through a long sheath. The catheter was then moved along the right ventricle and tricuspid annulus using real-time MRI guidance. Electrograms were recorded, and the filtered signal to noise ratio was 40. No myocardial capture was seen due to current induction, and no complications occurred in this setting.
The authors document the feasibility of performing atrial and ventricular electrogram recording, atrial and ventricular pacing, and movement of an electrophysiology catheter in these chambers using real-time MRI guidance in currently available 1.5 Tesla machines. No evidence of inadvertent pacing or myocardial heat damage due to changing magnetic gradients was seen. Future refinement of the safety and feasibility of this new technique is necessary, but it may allow for catheter movement with a reduction of radiation to both the patient and physician.
-- The opinions expressed in this commentary are not necessarily those of the editors or of the American Heart Association --