SOAR: Study Observing Antiarrhythmic Remodelling Using LGE-MRI

BACKGROUND AND INTRODUCTION:

Atrial fibrillation (AF) arises as a result of a complex interaction between triggers, perpetuators and substrate. As early as 1995, Morillo et al have demonstrated that AF is associated with ultrastructural changes in myocytes. In animal models, alterations in myocytes after sustained AF resemble those of myocardial hybernation with a phenotypical adaptation towards a more fetal stage. Ultimately, these structural changes would lead to Calcium overload and metabolic stress, similar changes have been observed in humans. However, in humans, atrial dilatation and degenerative changes have been observed. Interstitial fibrosis (caused by deposits of collagen and fibronectin) is the prime cause of structural remodeling in left atrium (Boldt et al., 2004). It has been well established that fibrosis is a confounding clinical factor in causing AF (Kostin et al., 2002). But AF itself promotes fibrosis, which in turn leads to increased conduction heterogeneity within the atrial substrate resulting in further progression of AF (Everett,and Olgin, 2007).

The recent introduction of Late Gadolinium enhancement magnetic resonance imaging (LGE-MRI) sequence now allows for non-invasive assessment of the location and extent of arrhythmia related fibrosis.

Contrast enhancement occurs as a result of altered washout kinetics of gadolinium relative to normal surrounding tissue, which may reflect increased fibrosis or tissue remodeling of the myocardium. Our group has demonstrated the feasibility of a new LGE-MRI acquisition and processing protocol to detect fibrosis in the LA.

To date, no controlled trials evaluating the effect of antiarrhythmic drugs (AAD) and regression of left atrial fibrosis as assessed by LGE-MRI has been performed. We propose to use LGE-MRI to evaluate the effects of dronedarone vs. placebo on atrial and ventricular fibrosis. It has been shown that the success of catheter ablation procedure (which has been shown to be superior in terms of maintaining sinus rhythm in AF patients when compared to anti-arrhythmic drugs) is dependent upon the extent of fibrosis (Akoum et al., in prep). In AF patients with greater than 35% enhancement (percent left atrial fibrosis), the success of catheter ablation in reducing AF recurrence is greatly reduced. Hence for these patients, a drug that can control the progression of fibrosis and simultaneously provide respite from AF recurrence would be an extremely desirable prescription.