Mapping Contact Force during Catheter Ablation for the Treatment of Atrial Fibrillation: New Insights into Ablation Therapy
The distribution of ablation catheter contact force may be important for elucidating the mechanisms of pulmonary vein (PV) reconnection following PV isolation (PVI) for the treatment of paroxysmal atrial fibrillation (PAF). A novel method was developed for the visualisation of tissue contact force on left atrial models derived from segmented MRI data and the approach was tested in 3 patients. The left atrium was automatically segmented from pre-procedural whole-heart cardiac magnetic resonance (CMR) scans in three patients undergoing circumferential PVI for catheter ablation of PAF. During the procedure, the CMR shell was overlaid on to real-time fluoroscopy using the EP Navigator (EPN) software (Philips Healthcare, The Netherlands) and registered using the trachea and intracardiac catheters. Using a wide area circumferential approach to encircle ipsilateral pairs of PVs, the position of each radiofrequency (RF) application (25W for 40s) was recorded on the CMR shell using the point tagging feature of EPN. Using a contact force-sensing ablation catheter (TactiCath, Endosense, Switzerland), the contact force-time integral (FTI) for each registered ablation point was recorded. The FTI for each point was then projected on to the CMR shell with a circular diameter of 10mm using custom-made software. This radius of force distribution was chosen to reflect the typical accuracy of location of the mapping catheter and also to take into account the motion of the catheter during the RF application.4 vein PVI and FTI maps were achieved in all patients (see figure 1 for example). The mean FTI applied to each side of the left atrium was recorded in gram seconds. The total and regional FTIs applied to achieve PVI differed between and within patients respectively, but in an inconsistent manner. The FTI map on the pre-segmented atrial shell provides an intuitive post-procedural assessment of the tissue-contact force achieved during RF delivery. The FTI is less consistent between patients for the RPVs than for the LPVs, perhaps reflecting patient-specific technical challenges. Comparison of FTI maps with post-ablation delayed enhancement, T2W MRI and clinical outcome data may assist in understanding the mechanisms of effective lesion delivery and of PV reconnection after ablation.