Cardiac MRI assessment of atrial fibrosis in atrial fibrillation: implications for diagnosis and therapy

Abstract

Atrial fibrillation (AF) is the most commonly encountered cardiac arrhythmia in clinical practice, with a prevalence of 0.4–1% in the US population.w1 AF is a potent risk factor, increasing the risk of stroke fivefold and accounting for approximately 15% of all strokes in the USA.w2 AF also significantly increases the risk of mortality from heart failure.w3–7 Many therapies, including pharmacological approaches and direct current cardioversion, have been tried to treat this malignant arrhythmia, but were not found to be that effective.1 w8–w11 Catheter ablation of AF has provided better outcomes compared with other treatments, especially by applying pulmonary vein (PV) isolation in patients with paroxysmal AF.2 w12 However, other procedures modifying the substrate of AF, such as complex fractionated atrial electrogram ablation3 or posterior wall debulking,4 are required to obtain satisfying results for persistent AF patients with massive left atrial structural remodelling (LASRM) caused by massive atrial fibrosis.w13 Since atrial fibrosis is one of the main factors determining AF relapse after catheter ablation, evaluating atrial fibrosis in AF subjects is now of increasing importance for AF ablation strategies. Nowadays echocardiography is the mainstream technique for detecting LASRM which may cause left atrial (LA) volume expansion and atrial conduction slowing and heterogeneity.w14–16 Late gadolinium enhancement (LGE) MRI has recently been proved to be a powerful tool for detecting atrial fibrosis. This article discusses the efficacy and implications of LGE-MRI assessment of atrial fibrosis in AF. ### Electrical remodelling: ‘AF begets AF’ Recognising that AF alters atrial electrophysiological properties and promotes AF induction and maintenance—that is, ‘AF begets AF’—is a breakthrough in AF pathophysiology.5 AF induces electrical remodelling primarily due to a very rapid atrial rate and associated tachycardia induced atrial remodelling. Action potential duration (APD) decreases during AF due to disruption of ion channel functions such as …