Can Imaging Revolutionize VT Ablations?
The challenge is obvious for the treating cardiologists and electrophysiologists. An increasing number of studies have demonstrated that new pharmacological treatments and ICDs can prolong the life of our heart failure patients. Over 200,000 patients currently have ICDs implanted in the US, and the number is rapidly growing — and so is the number of patients with appropriate ICD shocks. The current ablation strategies still rely mostly on our concepts of voltage mapping and substrate modification, as only a minority of patients will have a stable VT that allows entrainment mapping.
Jacques de Bakker had elegantly demonstrated in the 70’s and 80’s that the postulated intra-scar pathways (or zig-zag lines of surviving myocardium) could indeed be histologically confirmed in the human and animal heart. With the advent of image-integration and advances in cardiac imaging, the delineation of the scar and its border zone can now be performed with a variety of different imaging techniques. Our laboratory and others have shown that nuclear medicine techniques such as PET or SPECT as well as anatomic imaging with CT is able to accurately predict the areas of low voltage. This enables the electrophysiologist to concentrate on the scar substrate early on and can avoid poor contact measurements disguising themselves as myocardial scar.
The best scar visualization is currently performed with magnetic resonance imaging (MRI). The work of several groups has demonstrated over the last decade that MRI can be performed with relative safety in ICD patients if stringent inclusion/exclusion criteria are applied. Exclusion criteria should include abandoned intravascular or any epicardial leads as well as new implants. We have found that – indeed - myocardial scar detected by MRI in a series of ICD patients was able to guide and facilitate the VT ablation.(1) In 64% of patients, only a limited voltage map was required and MRI was able to detect heterogeneous, critical scar components intramyocardially or within large compact scar areas.
The big question will be if scar imaging is able to define successful ablation sites with high accuracy. Initial animal data collected from several groups is promising and the inclusion of the grey/heterogenous zone in the MRI analysis will likely provide new insights. I don’t think we should expect imaging to be able to replace signal interpretations and all of the traditional mapping. However, in 2011, I firmly believe that the experience of the last decade provides us with a roadmap to a faster and hopefully more effective ablation procedure.
1. Dickfeld et al. Circ Arrhythm Electrophysiol 2011 Jan 26 [Epub].
Timm Dickfeld, MD, PhD is the Chief of Electrophysiology at the VA Baltimore, Associate Professor of Medicine at the University of Maryland, and Founder of the Maryland Arrhythmia and Cardiology Imaging Group (MACIG).