Abstract 15488: Cardiac Magnetic Resonance T1 Mapping of Left Atrial Myocardium

Abstract

Introduction: Magnetic resonance imaging (MRI) T1 mapping is an emerging tool for objective assessment of myocardial fibrosis.

Hypothesis: T1 mapping for left atrial (LA) myocardium in patients with atrial fibrillation (AF) is feasible.

Methods: MRI (1.5 Tesla) was performed in 51 consecutive patients (64% males, median age 55 years, inter-quartile range (IQR) 51-65 years) prior to AF ablation (53% prior to first ablation, 47% prior to repeat ablation) and in 16 healthy volunteers (31% males, median age 26 years, IQR 23-30 years). Vertical long-axis planes were acquired using the Modified Look-Locker Inversion-recovery (MOLLI) sequence. T1 measurements were obtained from regions of interest placed on the posterior wall of the left atrium using Mass Research software (Medis, The Netherlands). Intra-cardiac point-by-point bipolar LA voltage maps were acquired at the beginning of ablation procedures using CARTO 3D electroanatomic mapping system (Biosense Webster).

Results: The median LA T1 relaxation time was shorter in patients with AF (387 ms, IQR 364-428 ms) compared to healthy volunteers (459 ms, IQR 418-532 ms, P<0.001) [Figure] and was shorter in AF patients with history of ablation compared to patients without prior ablation (P=0.035). Each 100 ms increase in T1 relaxation time was associated with 0.1 mV increase in intra-cardiac bipolar LA voltage after adjustment for age, prior ablation, type of AF, hypertension and diabetes in a generalized estimating equations model clustered by subject (P=0.019).

Conclusion: MRI T1 mapping of the LA myocardium is feasible and may improve the quantification of fibrotic changes in LA myocardium. Shorter average T1 times, indicating increased fibrosis, were observed with prior ablation attempts as a preliminary validation tool for this assay.