Abstract 17528: Quantitative MRI Assessment of LV Structural Remodeling and Fibrosis Formation in Canine Models of Chronic Atrial Fibrillation

Abstract

INTRODUCTION: Atrial fibrillation(AF) and heart failure(HF) are two “epidemics” of cardiovascular disease which often co-exist. We sought to characterize non-invasively the development and progression of left ventricular(LV) structural remodeling and fibrosis formation induced by AF in canine models with chronic AF.

METHODS: Eight mongrel dogs were implanted with a pacemaker to induce chronic AF via rapid atrial pacing(RAP). Each animal MRI was performed in sinus rhythm (cardioversion) and under anesthesia on a Siemens 3T scanner at baseline and once per month after RAP. Cardiac longitudinal relaxation time(T1) measurements were made by acquiring two single-shot balanced-steady-state-of-free-precession (b-SSFP) MR images (proton density and saturation-recovery image with recovery time=600ms), prior to and 15 min post extracellular contrast agent administration(Multi-hance,0.15mmol/kg). Cardiac T1 was calculated using the Bloch equation describing T1 relaxation. The partition coefficient, which reflects the extracellular space interrogated by the contrast agent, was calculated using the pre-contrast and post-contrast T1 measurements of the LV blood pool and myocardium.

RESULTS: Cardiac T1 maps decreased with RAP duration, whereas the partition coefficient increased with RAP duration(Figure1). These MRI findings were corroborated with histological assessment of tissue biopsies (Figure2: H&E and trichrome stained specimens).

CONCLUSIONS: Cardiac T1 MRI method can be used to measure non-invasively the LV structural remodeling and fibrosis formation induced by AF. Future studies include validation of MRI assessment of LV fibrosis against histology.