Temporal left atrial lesion formation after ablation of atrial fibrillation

Background

Atrial fibrillation (AF) ablation uses radiofrequency (RF) energy to induce thermal damage to the left atrium (LA) in an attempt to isolate AF circuits. This injury can be seen using delayed enhancement magnetic resonance imaging (DE-MRI).

Objective

The purpose of this study was to describe DE-MRI findings of the LA in the acute and chronic stages postablation.

Methods

Twenty-five patients were scanned at two time points postablation. The first group (n = 10) underwent DE-MRI at 24 hours and at 3 months. The second group (n = 16) was scanned at 3 months and at 6 or 9 months. One patient had three scans (24 hours, 3 months, 9 months) and was included in both groups. The location and extent of enhancement were then analyzed between both groups.

Results

The median change in LA wall injury between 24 hours and 3 months was −6.38% (range −11.7% to 12.58%). The median change in LA wall injury between 3 months and later follow-up was +2.0% (range −4.0% to 6.58%). There appears to be little relationship between the enhancement at 24 hours and 3 months (R² = 0.004). In contrast, a strong correlation is seen at 3 months and later follow-up (R² = 0.966). Qualitative comparison revealed a stronger qualitative relationship between MRI findings at 3 months and later follow-up than at 24 hours and 3 months.

Conclusion

RF-induced scar appears to have formed by 3 months postablation. At 24 hours postablation, DE-MRI enhancement appears consistent with a transient inflammatory response rather than stable LA scar formation.

Keywords: Atrial fibrillation, Pulmonary vein antrum isolation, Left atrial scar, Delayed enhancement MRI, Catheter ablation, Radiofrequency energy