Temporal left atrial lesion formation following ablation of atrial fibrillation: Lessons learned from delayed enhancement MRI

Background. Pulmonary vein antrum isolation (PVAI) uses radiofrequency (RF) energy to induce thermal damage to the left atrial (LA) substrate in an attempt to isolate atrial fibrillation (AF) circuits. This LA tissue injury can be seen using delayed enhancement MRI (DE-MRI). Methods. A group of twenty-five patients who presented for PVAI were scanned serially at two different time points. The first group (n = 10) of patients had DE-MRI acquired twenty four hours and three months following PVAI. The second group (n = 16) were scanned three months and six months following PVAI. Three dimensional models of the LA were created and analyzed to determine structural change. The extent of scar formation was analyzed using an automated computer algorithm based on dynamic thresholding. Results. The median change in LA wall injury between 24 hours and 3 months (Group 1) was –6.38% (range = -11.7% to 12.58%). The median change in LA wall injury between 3 months and later follow-up (Group 2) was +2.0% (range = -4.0% to 6.58%). Qualitative comparison of LA scar patterns revealed a stronger qualitative relationship between MRI scans acquired at 3 months and later follow-up than at 24 hours and 3 months. There appears to be little relationship between the extent of scar at 24 hours and that detected at three months (R = 0.004). In contrast, a strong correlation is seen at 3 months and later follow-up (R = 0.966). Conclusion. RF-induced scar as measured by DE-MRI following PVAI appears to have formed by three months post-ablation. Scar patterns remain consistent in their extent, location and intensity at later follow-up. At 24 hours following the procedure, DE-MRI enhancement appear consistent with a transient inflammatory response rather than stable LA scar formation.