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CMR of Arrhythmia and Ablation

Non-invasive Imaging: Magnetic Resonance Imaging

During the CMR of Arrhythmia and Ablation session on Friday afternoon the audience were treated to a cutting edge glimpse into the important future role of cardiovascular MRI in managing patients with arrhythmia.

The session started with a presentation from David Bluemke from the NIH who gave a comprehensive review of the evidence relating to the presence of ventricular scar by LGE and the occurrence of arrhythmia and adverse outcomes, both in ICM and NICM. However, our current methods of identifying scar remains subjective, especially in the context of the scar borderzone (“gray zone”), which need to be standardized. Overall though CMR remains key in this field and “increasingly these studies will be able to compare size and location of scar to likelihood of event”, according to Dr Bluemke. (Pic 1)

The following presentation, by Oleg Aslanidi from Kings College London was a fascinating insight into the role of our computer modelling colleagues in improving our understanding of the pathogenesis of arrhythmia, and the important role that CMR plays in providing the detailed individual anatomical and scar information required in order to construct these complex and personalized models of arrhythmia. Examples including left atrial remodelling, left atrial fibrosis and left atrial wall thickness are all important components in the complex current simulations of atrial fibrillation that are changing the way we understand these rhythm disorders and paving the way towards an individualized strategy of ablation based upon patient specific CMR characteristics. (Pic 2)

Saman Nazarian from Johns Hopkins University presented compelling evidence for the additive value of CMR scar imaging to facilitate the ablation process by providing visual information about the quality of the ablation lesion by a different method to the current electroanatomic method. Whilst the current electrophysiological method identifies scar by its electrical properties, ablation failures are frequently due to recovery of areas that were incorrectly identified as full thickness lesions. Dr Nazarian highlighted the potential future role of LGE to identify gaps in a line of ablation that would predict failure, and for the identification of ventricular mid-wall scar that will often not be identified either from mapping from the endocardial or epicardial surface. Comparison of scar maps during VT ablation reveal that MRI can be used to identify regions of full thickness infarction within which the electrophysiologist can look to ablate the surviving key central circuit which is the cornerstone to a successful ablation.

The following presentation by Professor Reza Razavi, again from Kings College London, took this principle a step further by presenting the groundbreaking development of cardiac ablation performed entirely under MRI imaging. The complexity of the management of some arrhythmias is well known, and even with the current era very sophisticated electrophysiological mapping systems success rates can be disappointing. The combination of electrical mapping with real-time MRI imaging is clearly very appealing as it adds the possibility of substrate identification, improved accuracy in catheter positioning, measurement of success of ablation by imaging the ablation lesion and potentially reducing complications by 3D real-time imaging of catheter movement. However, there are significant technical and safety hurdles to performing a cardiac ablation inside an MRI scanner. Reza Razavi and his team have overcome these hurdles and have now performed 8 clinical MRI guided atrial flutter ablations. This demonstrates the feasibility of such a strategy, and future exciting developments are likely to see this strategy being deployed for more complicated rhythms. (Pic 3)

The final presentation, by Graham Wright of Sunnybrook Research Institute presented exciting research developments into the role of non-contrast T1 in identifying ablation lesions by MRI. Previous studies looking at T2 imaging for oedema, and LGE for scar but perhaps non-contrast T1 will actually be the best measure. On heating myocardial tissue during radiofrequency ablations results in a change in the intracellular iron form which is detectable by T1 sequences. Studies in a canine model have shown that the T1 images shortly after ablation are a better predictor of scar appearance at 3 months than the conventional LGE method. (Pic 4)

Overall this is clearly a very exciting time for collaboration between CMR and electrophysiology. The use of LGE in the management of IHD has revolutionized the management of coronary artery disease over the last 15 years and it may be that we are now standing on the verge of the next big step forward in the management of complex arrhythmias, and I can’t wait.

The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.