Abstract
Objectives: In atrial fibrillation (AF), diffuse myocardial fibrosis may be induced by arrhythmia or reflect pre-existing cardiomyopathy. The presence of concurrent AF and diffuse myocardial fibrosis has been associated with an increased risk of heart failure progression.Unlike focal fibrosis, diffuse myocardial fibrosis is not visualized on delayed enhancement magnetic resonance imaging (MRI), but can be quantified with ECV fraction. Hypothesis: The extracellular volume (ECV) fraction may provide new insights to evaluate diffuse myocardial fibrosis of the left ventricle (LV) in patients with AF. Methods: 78 subjects underwent MRI using a clinical 3 T scanner (Magnetom Verio, Siemens Healthcare): 25 persistent AF patients, 28 paroxysmal AF patients and 25 controls. Left-atrial volume was evaluated from MR cine imaging. A validated Look-Locker T1 Mapping Siemens prototype sequence was used to generate T1 maps as an index of diffuse myocardial fibrosis. The imaging parameters were: TE/TR = 1/295.33ms, FOV = 360mm, Slice Thickness = 8mm, image matrix = 192. 3 short axes of pre and post T1 maps were acquired as shown in Figure 1. ECV fraction was calculated from T1 maps acquired pre- and post-contrast calibrated by blood hematocrit. The ECV fraction was calculated as:ECV=(1-hematocrit)(1/(T1my post)-1/T1myopre)/(1/(T1blood post)-1/T1bloodpre) Results: AF patients had larger left atrial volume (persistent AF: 175.7±65.9ml; paroxysmal AF: 116.7±43.6ml) than controls (76.6±12.8ml) (paroxysmal vs. control: P<0.01; persistent vs. control: P<0.01). Mean ECV of persistent AF patients was 31.8±3.9% in the basal segments, 30.5±4.8% in the mid-cavity segments, 32.0±4.8% in the apical segments, paroxysmal AF patients were 29.2±3.6%, 28.2±3.5%, 31.5±4.6% respectively, which were higher than the controls (basal: 24.7±2.3%, mid-cavity: 25.9±2.4%, apical: 28.2±4.0%, all P<0.05). Conclusion: ECV fraction could help to identify the diffuse LV fibrosis in patients with AF. The quantification could be a better solution for clinicians in diagnosing diffuse LV fibrosis.
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