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Why hesitate introducing real-time magnetic resonance imaging into the electrophysiological labs?

Matthias Koopmann, Nassir F. Marrouche
DOI: http://dx.doi.org/10.1093/europace/eus331 7-8 First published online: 8 October 2012

This editorial refers to ‘Feasibility of real-time magnetic resonance imaging-guided electrophysiology studies in humans’ by P. Sommer et al., on page 101

Catheter ablation using a standard fluoroscopy imaging guidance provides a cure for a plethora of cardiac arrhythmias and has become the cornerstone of arrhythmia management.1 Nevertheless, since the introduction of complex arrhythmias ablation into the electrophysiological (EP) labs, the need for more accurate imaging visualization and guidance tools has emerged. Despite the massive amount of research and financial investments into the novel ablation and imaging modalities, the outcome of complex ablation procedures has not improved, in fact it has been stable for the last decade. For example, atrial fibrillation (AF) ablation success rates are still reported to be between 40 and 80%.24 This dilemma, however, prompted interest in an alternative, complete ‘outside of the box’, concept. One of the imaging/ablation modalities, which has been suggested, is real-time magnetic resonance imaging (MRI)-guided interventional procedure. Cardiac MRI is considered a great tool to help detecting the anatomy, function, and viability of the myocardium.5 Moreover, MRI imaging is an ideal method to detect and quantify critical myocardial arrhythmogenic substrates such as fibrotic and scar tissue in the atria6,7 and the ventricles.810

Current evidence

In this issue of the journal, Sommer et al.11 report their first experience with real-time MRI-guided EP procedures. The motivation for this study was to gain experience in catheter visualization in the human beating heart using passive catheter tracking, and to perform diagnostic EP studies. The study population consisted of five consecutive patients referred for ablation of symptomatic arrhythmias: three patients had isthmus ablation for typical atrial flutter, one patient with atrioventricular node reentry tachycardia underwent slow pathway modulation, and one patient was referred for a diagnostic EP study for unexplained syncope. All procedures were successfully conducted in a conventional EP lab with fluoroscopy guidance, using conventional diagnostic and ablation catheters. After the procedure, patients were transferred to an MRI scanner (1.5 T; Gyroscan Intera CV: Philips), for testing the feasibility and safety of EP studies guided by MRI. Two MRI compatible catheters (Vision™; Imricor Medical Systems), with non-ferromagnetic components to reduce MR-induced heating, electrical noise, and image artefacts, were inserted and were successfully visualized and navigated within the heart using a passive catheter tracking system. Catheters were navigated to the right atrium and the right ventricle; anatomical orientation was additionally verified by local electrograms. Using special noise reduction systems, recording of electrograms was successful in all cases. Although His-bundle catheter placement was achieved, the authors were not able to reproduce His-electrogram recordings. Programmed stimulation for both right atrial and ventricular sites was performed via two MRI compatible catheters. No significant complications have been reported in this series. The authors have concluded that real-time MRI is safe and feasible for mapping and ablation during right-sided procedures. The authors should be congratulated on a major step towards a complete MRI-guided ablation procedure.

Initial attempts to investigate real-time MRI-guided ablation procedures were performed over a decade ago. Lardo et al.12 demonstrated the ability of performing EP studies, visualizing catheters, and inducing radiofrequency tissue lesions under real-time MRI guidance. Further reports followed on drug injection into the left ventricular wall via a retrograde femoral arterial approach under real-time guidance in swines.13,14 In 2008, Nazarian et al.15 reported the first successful EP study in two patients, including accurate catheter tracking (active and passive), intracardiac ECG recording, and pacing manoeuvres in the MRI environment. While thus far radiofrequency ablations were targeted at arbitrary anatomic locations within the heart, Hoffmann et al.16 recently reported the first cavotricuspid isthmus ablation in pigs, as a well-known specific EP anatomic target. We also were the first to tackle the difficult task of real-time MRI-guided atrial ablation and demonstrated the ability of real-time detection and monitoring of atrial lesion formation in a 3 T MRI scanner.17

Real-time MRI may have major attractive features for the interventional electrophysiologist that would help significantly to improve the procedural efficacy and safety. The following has already been demonstrated by multiple groups or investigators: (i) good visualization of myocardial soft tissue composition, thus helping to identify critical arrhythmogenic substrate; (ii) ability of arbitrary two-dimensional image views and three-dimensional reconstruction in conjunction with orthogonal and perpendicular catheter visualization in real time; and (iii) real-time monitoring of critical adjacent cardiac structures, e.g. the pericardial space, the oesophagus, or the pulmonary veins, to reduce possible fatal complications during lesion formation and energy delivery (visualization and monitoring of lesion formation).

Major hurdles and personal perspective

Despite all the efforts and positive reports over the past 12 years demonstrating the safety and feasibility of real-time MRI, this modality is struggling to make it to the EP labs.18 Why hesitate to bring real-time MRI to prime time? Why are we slow in moving forward despite the fact that three points mentioned above have been achieved, and this modality is ready for use in every EP-MRI lab. Nevertheless, the pace of clinical research and developments is still slow. Hurdles remain but hopefully will be alleviated by improving the collaboration between electrophysiologists and radiologists and between catheter and scanner manufacturers.

From a personal point of view and after an extensive experience in various ablation modalities over the last 15 years, there seems to be no alternative for real-time MRI short or long term to make the complex arrhythmia procedures safer and more efficient.

Conflict of interest: none declared. 

Funding

M.K. received a stipend from the ‘deutsche Herzstiftung’ (Mit Fördermitteln der deutschen Herzstiftung e.V.).

Footnotes

  • The opinions expressed in this article are not necessarily those of the Editors of Europace or of the European Society of Cardiology.

References