Background: Catheter ablation has become an established therapy for patients with symptomatic atrial fibrillation (AF). Atrial fibrosis is associated with initiation and maintenance of AF and therefore a potential ablation target. Invasive 3D-electroanatomical mapping can visualize left atrial low voltage areas suggestive for fibrosis. Preprocedural imaging may help to identify patients at risk for relevant fibrosis even before AF ablation and therefore facilitate procedural planning.

Aims: The aim of this study was to investigate direct correlations between magnetic resonance imaging (MRI)-derived left atrial functional parameters and the individual amount and distribution of left atrial fibrosis from 3D-electroanatomical mapping in patients undergoing AF ablation.

Methods: Patients scheduled for index AF ablation and preprocedural cardiac MRI were included into this study. All patients were in stable sinus rhythm at timepoint of cardiac MRI. Left atrial strain (LAS) and left atrial strain rate (LASR) were assessed by feature tracking. All patients underwent radiofrequency based pulmonary vein isolation (PVI) and 3D-electroanatomic mapping of the left atrium using a multipolar mapping catheter. Left atrial low voltage areas were defined as areas with voltage <0.5mV. Presence of low voltage areas was classified according to the fibrotic atrial cardiomyopathy (FACM)-score and statistically analyzed regarding correlation to left atrial functional parameters. Statistical analysis included comparison of linear values between study groups with students t-test and analysis of linear correlations between groups with the Kruskal-Wallis test.

Results: Twenty-six patients were included into the study. Ten patients (38.5%) were male and mean age was 67.7±8.7 years. Twenty-two patients (84.6%) suffered from a persistent state of AF at the time of ablation while 4 patients (15.4 %) presented with paroxysmal AF. In the majority of patients (65.4%) 3D-electroanatomical mapping did not reveal left atrial low voltage areas. In 34.6% of the patients left atrial low voltage areas were observed. In 77.8% of these patients a FACM-score of 3 or 4 was present indicating relevant or severe fibrosis while the rest of the patients showed a FACM-score of 1 or 2 indicating a lower degree of fibrosis. Patients with atrial fibrosis were older (p=0.002) and showed higher LA volumes (p<0.001). MRI-based left atrial functional parameters including global longitudinal left atrial reservoir strain, conduit strain, booster strain as well as reservoir strain rate, conduit strain rate and LA-EF were significantly reduced in patients with atrial fibrosis (p=0.002, p=0.003, p=0.023, p=0.006, p=0.004 and p<0.001, respectively). There was a significant linear correlation of FACM scoring with LA-EF (p=0.012), LA volume (p=0.035), reservoir strain (p=0.030) and conduit strain (p=0.003) as well as reservoir strain rates (p=0.021) and conduit strain rates (p=0.032).

Conclusion: Left atrial functional parameters derived from cardiac MRI show a significant correlation to 3D-electroanatomical mapping detected left atrial low voltage areas. Assessment of left atrial functional parameters by MRI may therefore be a useful non-invasive preprocedural imaging strategy for fibrosis estimation facilitating procedural planning in patients scheduled for catheter ablation.