Letter from the Editor in Chief

DOI: 10.19102/icrm.2012.031101

John Day, MD, FHRS, FACC

Editor-in-Chief

Dear Readers,

For this month's letter, I would like to comment on the excellent case report from Dr. Moussa Mansour and colleagues from Massachusetts General Hospital. In this case, they were able to show how a pre-ablation MRI was able to clearly delineate areas of atrial scar that then allowed them to correctly identify two atypical flutter circuits later encountered in the ablation of a patient with longstanding, drug-refractory persistent atrial fibrillation and atrial flutter.

For a number of years now, we have heard reports from several centers about how wonderful delayed enhancement MRI (DE-MRI) is for delineating myocardial fibrosis as a guide to ablation or as a means to identify patients at risk for sudden cardiac arrest who may require defibrillator therapy. The question then is, is DE-MRI now ready for prime time use? Should all centers that perform ablations or device implantations have access to this technology?

I must admit, the atrial MRI images provided in this case report are really quite spectacular. Unfortunately, most centers simply cannot reproduce these kinds of atrial MRI images. For most centers, the resolution of atrial scar is just not anywhere near what was shown to us in this case. As DE-MRI protocols become more standardized and as the technology improves then other centers will be able to generate the type of scans we have seen from Massachusetts General Hospital.

While it is still extremely challenging to get good enough resolution with DE-MRI to see small channels or foci of atrial scar, it is a completely different story in the ventricle. With imaging of the ventricles, MRI images can show the extent of scar, if it is endocardial, mid, or epicardial in location, and it can show channels for VT ablation. Many centers are currently using MRI to help in VT ablation planning and approach. In addition, many centers are also using MRI as a means to help identify patients who may benefit from ICD therapy for conditions such as hypertrophic cardiomyopathy, arrhythmogenic right ventricular dysplasia, and other conditions. Indeed, unlike atrial fibrosis imaging, imaging of ventricular fibrosis by this technique is very reproducible and the images are really quite impressive.

One particular challenge with using MRI to guide VT ablation is that many of these patients already have an ICD in place. At our center we have now done over 100 chest MRIs in patients with defibrillators and have not seen any significant complication. These pre VT ablation MRI scans have really helped us in guiding us as to whether we need an endocardial and/or epicardial approach to our ablation. With experience, we have found that MRI can minimize the need for extensive ablation as we can focus on the channels. For idiopathic VT, it is important in ruling out early structural heart disease and identifying intra-cavitary anomalies (false tendons, aberrant papillary muscles, and left ventricular or right ventricular bands) that may be the source of an arrhythmia.

What is the current state of the art for DE-MRI imaging for AF ablations? Right now, the primary role is that it can be a good screening tool to help us identify patients who may not be suitable for ablation. In other words, those patients with persistent AF and extensive scarring by MRI may not be good candidates for AF ablation as the success rate for these patients will be significantly lower.

Will we ever be able to perform real time MRI guided ablations? Unfortunately at this time it is just not reasonable feasible. The magnets themselves present an obstacle, many patients do not tolerate MRIs well, and the non-ferrous equipment required need to be significantly improved. Moreover, it takes about an hour to produce a high quality MRI study. For a busy EP practice I'm just not sure how they would get through the day doing repeated MRIs as part of an ablation procedure. However, despite these limitations, MRI is currently the best imaging modality we have and if MRI can be incorporated into the EP lab it would be a significant benefit for our procedures.

I hope you enjoy this issue of the Journal and that the education provided continues to benefit you in your practice. As always, I look forward to hearing your comments.

Warm regards,

Editor-in-Chief

John Day, MD, FHRS, FACC
Editor-in-Chief
The Journal of Innovations in Cardiac Rhythm Management
JDay@InnovationsInCRM.com
Director of Heart Rhythm Services
Intermountain Medical Center
Salt Lake City, UT