Atrial fibrillation ablation outcome is predicted by left atrial remodeling on MRI

Abstract

Background: Although catheter ablation therapy for atrial fibrillation (AF) is becoming more common, results vary widely, and patient selection criteria remain poorly defined. We hypothesized that late gadolinium enhancement MRI (LGE-MRI) can identify left atrial (LA) wall structural remodeling (SRM) and stratify patients who are likely or not to benefit from ablation therapy.

Methods and results: LGE-MRI was performed on 426 consecutive patients with AF without contraindications to MRI before undergoing their first ablation procedure and on 21 non-AF control subjects. Patients were categorized by SRM stage (I-IV) based on the percentage of LA wall enhancement for correlation with procedure outcomes. Histological validation of SRM was performed comparing LGE-MRI with surgical biopsy. A total of 386 patients (91%) with adequate LGE-MRI scans were included in the study. After ablation, 123 patients (31.9%) experienced recurrent atrial arrhythmias during the 1-year follow-up. Recurrent arrhythmias (failed ablations) occurred at higher SRM stages with 28 of 133 (21.0%) in stage I, 40 of 140 (29.3%) in stage II, 24 of 71 (33.8%) in stage III, and 30 of 42 (71.4%) in stage IV. In multivariate analysis, ablation outcome was best predicted by advanced SRM stage (hazard ratio, 4.89; P<0.0001) and diabetes mellitus (hazard ratio, 1.64; P=0.036), whereas increased LA volume and persistent AF were not significant predictors. LA wall enhancement was significantly greater in patients with AF versus non-AF controls (16.6±11.2% versus 3.1±1.9%; P<0.0001). Histological evidence of remodeling from surgical biopsy specimens correlated with SRM on LGE-MRI.

Conclusions: Atrial SRM is identified on LGE-MRI, and extensive LGE (≥30% LA wall enhancement) predicts poor response to catheter ablation therapy for AF.

Keywords: atrial remodeling; catheter ablation; magnetic resonance imaging.

Figure 1

Segmentation process used for quantification of LA wall fibrosis. Panel A shows single slice level from 3D late gadolinium enhancement data set pre-ablation. Panel B shows endo and epi contours of the LA wall used for determining degree of fibrosis. Panel C shows abnormal, fibrotic regions in green and normal, non-fibrotic tissue in blue. Panel D shows 3D reconstruction of the entire data set separated to highlight the specific slice level in this example.

Figure 2

Four stages of LA structural remodeling (SRM) based on 3D late gadolinium enhancement (LGE) MRI scans. Representative examples from patients in each stage of LA remodeling in PA views (above examples of stages I–IV are 3%, 13%, 26%, and 56%, respectively). Normal LA wall displayed in blue with SRM changes in green. The pulmonary veins are shown in grey.

Figure 3

Kaplan-Meier rates of AF recurrence. Post AF ablation recurrences according to four stages of atrial structural remodeling over 1-year follow-up period.

Figure 4

LA wall structural remodeling on LGE-MRI correlates with surgical biopsy specimens. Examples from 3 surgical patients who underwent both 3D LGE-MRI scanning and biopsy of the LA wall. “Control’ patient without AF shown left (1a–1c), AF patient with moderate amount of SRM in center (2a–2c), and AF patient with advanced SRM on right (3a–3c). 3D LGE-MRI renderings show fibrosis/structural remodeling (SRM) in green with normal tissue in blue (top panels). Masson’s trichrome stains collagen blue and LA myocytes red (middle panels standard staining, bottom panels are subtraction images). Red box shows biopsy location.