Ablation and hydrogel injection in beating heart and approach to cardiac mapping
Upon establishing the ex vivo suspension and stable function of the heart, patches were attached around the basin to permit ex vivo electroanatomical mapping (EAM; CARTO3 system, Biosense Webster, Diamond Bar, CA, USA). A 3.5 mm tip irrigated ablation catheter (ThermoCool Navistar; Biosense Webster, Diamond Bar, CA, USA) was used to perform both mapping and focal ablation. First, during normal sinus rhythm, point-by-point mapping of the epicardial surface of the lateral left ventricle was performed. Each point was adjudicated to establish an appropriate timing reference. After this, a point with homogeneous conduction and voltage was selected within the mapped region as a target for ablation at 30 Watts for 1 minute with normal saline irrigation at 30 ml/min. We then remapped the region including within the scar region and around in regions of normal tissue. The hydrogel was then injected using an 18-gauge needle by sequentially injecting circumferentially around the area of ablated myocardium by pushing the needle into the tissue and slowly injecting the hydrogel as it was withdrawn with each injection. Injections were then performed in perpendicular lines spaced evenly 1 mm apart through the center of the lesion in a grid pattern. After this, remapping was done of the region with again careful attention to annotation of individual points. The time between injection and remapping was within minutes. All mapping was done during sinus rhythm.