Detection and quantification of left atrial structural remodeling with delayed-enhancement magnetic resonance imaging in patients with atrial fibrillation

Abstract

Background: Atrial fibrillation (AF) is associated with diffuse left atrial fibrosis and a reduction in endocardial voltage. These changes are indicators of AF severity and appear to be predictors of treatment outcome. In this study, we report the utility of delayed-enhancement magnetic resonance imaging (DE-MRI) in detecting abnormal atrial tissue before radiofrequency ablation and in predicting procedural outcome.

Methods and results: Eighty-one patients presenting for pulmonary vein antrum isolation for treatment of AF underwent 3-dimensional DE-MRI of the left atrium before the ablation. Six healthy volunteers also were scanned. DE-MRI images were manually segmented to isolate the left atrium, and custom software was implemented to quantify the spatial extent of delayed enhancement, which was then compared with the regions of low voltage from electroanatomic maps from the pulmonary vein antrum isolation procedure. Patients were assessed for AF recurrence at least 6 months after pulmonary vein antrum isolation, with an average follow-up of 9.6+/-3.7 months (range, 6 to 19 months). On the basis of the extent of preablation enhancement, 43 patients were classified as having minimal enhancement (average enhancement, 8.0+/-4.2%), 30 as having moderate enhancement (21.3+/-5.8%), and 8 as having extensive enhancement (50.1+/-15.4%). The rate of AF recurrence was 6 patients (14.0%) with minimal enhancement, 13 (43.3%) with moderate enhancement, and 6 (75%) with extensive enhancement (P<0.001).

Conclusions: DE-MRI provides a noninvasive means of assessing left atrial myocardial tissue in patients suffering from AF and might provide insight into the progress of the disease. Preablation DE-MRI holds promise for predicting responders to AF ablation and may provide a metric of overall disease progression.

Figure 1. MRI relationship with EA map in posterior (PA) and right anterior oblique (RAO) views

(A) Segmented DE-MRI reveals discrete areas of enhancement in the posterior wall and the septal area. (B) Color 3D models improve dynamic range and better illuminate enhancement patters. (C) EA map acquired during invasive EP study. Discrete patterns of low voltage (within bounded white lines) were detected in the left posterior wall and the septum in the patient shown which correlate with the regions of DE-MRI enhancement.

Figure 2. Three Dimensional MRI models for Two Healthy Volunteers

(A) Two dimensional slice from the DE-MRI scan. (B) Posterior (PA) view of reconstructed 3D MRI model. (C) Right anterior oblique (RAO) view of the 3D MRI model which shows the inter-atrial septum and the anterior wall. In all volunteers, MRI reveals uniform LA tissue enhancement.

Figure 3. Three-Dimensional MRI Models in Two Patients with Mild Structural Remodeling

(A) Two dimensional slice from DE-MRI scan. (B) 3D DE-MRI reveals minimal contrast enhancement. (C) 3D color models. (D) EA map showing electrically normal (purple) and abnormal (colored) atrial tissue. The EA map illustrates homogeneous voltages throughout much of the left atrium with small patches of electrically abnormal/low voltage tissue in nearly all patients who successfully responded to PVAI therapy. Abnormally enhanced regions on MRI correlate closely with low voltage areas on the EA maps.

Figure 4. Three-Dimensional MRI Models in Two Patients with Moderate Structural Remodeling

(A) Two dimensional slice from DE-MRI scan. (B) Segmented DE-MRI reveals increased enhancement in portions of the poster LA wall. (C) MRI images as color 3D models clearly show large regions of abnormal enhancement (green) in comparison to healthy tissue (blue). (D) EA map shows large patches of electrically normal (purple) and abnormal tissue (colored). Electrically non-viable (scar) tissue is shown in red. The most substantial enhancement appears in the posterior wall of the LA, which correlates with the enhancement seen on MRI.

Figure 5. Three-Dimensional MRI Models in Two Patients with Extensive Structural Remodeling

Both patients shown suffered a recurrence of atrial fibrillation. (A) Two dimensional slice from DE-MRI scan. (B) Segmented DE-MRI reveals large amounts of enhancement in various regions of the LA including anterior wall, posterior wall and septum. (C) MRI images as color 3D models show abnormally enhanced regions (green). (D) EA maps show large regions of electrically non-viable tissue (fibrotic scar) in red interspersed with electrically abnormal tissue (colored).

Figure 6. Correlation between enhancement on DE-MRI and low voltage regions on EA Map

Linear regression between the extent of enhancement seen on 18 segmented LA models of DE-MRI and the amount of low voltage tissue seen on 18 segmented EA map graded by blinded reviewers.

Figure 7. Patients in normal sinus rhythm following ablation of the left atrium

Cox regression curves for patients with mild enhancement (blue), moderate enhancement (green) and extensive enhancement (red) are shown. The mean follow-up was 9.6 ± 3.7 months (range = 6 to 19 months).