PO-01-084 HIDING IN PLAIN SIGHT

Abstract

Substrate based scar modification requires accurate detection and characterization of myocardial scar in sinus rhythm or using different wavefronts of activation. Mapping during ventricular tachycardia can be performed only in about 30% to 40% cases. We describe a challenging case of scar VT with discrepancy in the delineation of scar between voltage mapping and cardiac MRI and the role of Decremental Evoked Potential Mapping as a guide to a more focussed ablation in such circumstances. N/A N/A 56 year diabetic female status post Coronary artery bypass grafting in 2016 and moderate left ventricular dysfunction with recurrent episodes of hemodynamically unstable ventricular tachycardia and patient's refusal for ICD was evaluated and cardiac MRI revealed subendocardial scar in the anterior wall and patent grafts on coronary angiogram. Patient was taken up for 3D mapping and ablation using 3.5 mm tip non force sensing unidirectional irrigation ablation catheter.In view of hemodynamically unstable VT, activation mapping was not possible, hence substrate mapping was planned. Endocardial bipolar voltage mapping didnot delineate any scar in sinus rhythm and after changing the wavefront of activation to right ventricular paced rhythm. Unipolar voltage map didnot show any scar. While mapping the anterior wall , abnormal local electrograms were seen superimposed into the far field electrograms. To do a foccussed ablation we applied the concept of Decremental Evoked Potential Mapping and identified the slow conduction zone - the most critical component of the scar for initiation and maintainence of re-entry. We identified and ablated only the points with abnormal local electrograms with absolute value of decrement more than 10 ms as part of slow conduction zone. Post ablation, VT was not inducible despite induction protocol using triple extrastimuli from two different sites. Activation mapping is not possible in hemodynamically unstable VT. Substrate based mapping needs accurate delineation of myocardial scar. As the 3D mapping system is an automated system and annotates only the largest amplitude signals for color coded voltage mapping, in cases without dense scar, voltage mapping doesnot reliably identify and delineate the scar when compared to cardiac MRI, particularly with a larger tip diameter ablation catheter. Novel mapping techniques like Decremental Evoked Potential Mapping enable limited ablation in such cases.