1CMR characterization of linear ablation lesions with varyng contact force – a chronic porcine model

Introduction: Catheter-myocardium contact force (CF) is a major determinant of ablation lesion generation, with higher CF associated with greater energy transfer. The effect of contact force on atrial lesion formation has not been characterized in an in vivo model. Acute and chronic atrial injury can be visualized with T2-weighted (T2W) and late gadolinium enhancement (LGE) cardiac magnetic resonance (CMR) and in combination with voltage mapping, histology and ex vivo MR provides the necessary tools for detailed ablation lesion characterization. We investigated the effect of contact force on lesion characteristics, including transmurality, acutely and 2 months after atrial ablation. Methods: Under general anaesthesia, femoral venous access was obtained in eight Gottingen minipigs. In two animals, pre-ablation CMR imaging was performed. Using an electro-anatomical mapping system (Carto3, Biosense Webster) the geometry of the right atrium was obtained with a 20-pole circular mapping catheter (Lasso Nav, D curve, Biosense Webster). An intercaval linear ablation lesion was created using a CF-sensing catheter (SmartTouch, Biosense Webster, 30W, 48C, 20ml/min irrigation). Target contact forces of >20g (high force) or <10g (low force) were used alternately at the cranial and caudal ends of the ablation line. After ablation, repeat CMR imaging of the ablation lesion was performed. CMR was repeated at 2 months before the animals were sacrificed. Ablation lesions were dissected en bloc and mounted in frames before ex vivo MR was performed. Finally, lesions were sectioned orthogonal to the axis of the ablation line to complete the assessment of transmurality. Result: Applied CF was 9.1±3.5g and 34.6±18.6g in the low and high CF regions. Qualitative analysis of chronic voltage mapping illustrated resolution of normal voltage in the low force ablation regions. Acute wall thickness (measured on T2W images) was significantly greater in the high CF region, for both the caudal (7.0mm vs. 4.6mm; p=0.016) and cranial (6.9mm vs. 4.6mm; p=0.038) ends of the ablation line (Fig. A). There were no significant differences between the mean T2W or LGE SI according to force in either the acute or chronic scans. Chronic lesion volume (LGE) was greater in high CF regions for the cranial, but not caudal, ends of the ablation line (Fig. B). Ex vivo MR and macroscopic sectioning confirmed full-thickness lesions were created in both low and high CF regions. Conclusion: Acute T2 CMR displays the extent of atrial wall injury following RF ablation and is proportional to CF, supporting a role for contact force monitoring during ablation. T2 and LGE CMR SI of ablation lesions at both acute and chronic timescales are similar regardless of the CF used during ablation, and lesion volume is only increased with high CF in certain regions of ablation. These findings suggest other ablation-related parameters including catheter stability may play a larger role in predicting chronic lesion formation. ![Graphic][1] [1]: /embed/inline-graphic-1.gif