Left Atrial Structural Remodelling in Non-Valvular Atrial Fibrillation: What Have We Learnt from CMR?

Abstract

Left atrial structural, functional and electrical remodelling are linked to atrial fibrillation (AF) pathophysiology and mirror the phrase “AF begets AF”. A structurally remodelled left atrium (LA) is fibrotic, dysfunctional and enlarged. Fibrosis is the hallmark of LA structural remodelling and is associated with increased risk of stroke, heart failure development and/or progression and poorer catheter ablation outcomes with increased recurrence rates. Moreover, increased atrial fibrosis has been associated with higher rates of stroke even in sinus-rhythm individuals. As such, properly assessing the fibrotic atrial cardiomyopathy in AF patients becomes necessary. In this respect, late-gadolinium enhancement cardiac magnetic resonance (LGE-CMR) imaging is the gold standard in imaging myocardial fibrosis. LA structural remodelling extension offers both diagnostic and prognostic information and influences therapeutic choices. LGE-CMR scans can be used before the procedure to better select candidates and to aid in choosing the ablation technique, during the procedure (full CMR-guided ablations) and after the ablation (to assess the ablation scar). This review focuses on imaging several LA structural remodelling CMR parameters, including size, shape and fibrosis (both extension and architecture) and their impact on procedure outcomes, recurrence risk, as well as their utility in relation to the index procedure timing.

Low voltage areas, atrial natriuretic peptides and fibrosis: Challenges and controversies

“…We read with great interest the excellent article written by Seewöster et al 1 In atrial fibrillation (AF), left atrial (LA) fibrosis and dysfunction, biomarkers as atrial natriuretic peptide (ANP), delayed enhancement areas and low voltage areas (LVAs) are related to atrial cardiomyopathy and atrial failure. 2,3 Indeed, NT-proANP could be a missing link in LVAs prediction, 1 but there are some issues.…”

“…LVAs detected by electroanatomical mapping are a surrogate for LA fibrosis, best assessed by late gadolinium enhancement. 3 The 0.5 mV threshold was arbitrarily chosen for LVAs. Despite this, fractioned electrograms seem to be exactly in these areas.…”

“…5 Both techniques lack agreement in protocols, which may lead to heterogeneities, and increased difficulties in comparing the two. 3 Therefore, it is difficult to use LVAs as outcome. However, if LVAs correlates with NT-proANP, why not also with LA volume?…”

Left atrial scar identification and quantification in sinus rhythm and atrial fibrillation

“…One such cause is from prolonged exposure to risk factors which promote fibrogenesis, such as hypertension, diabetes, or congestive cardiac failure. 8,9 Myocyte loss and fibrosis results in a reduction of ion channels and fibers which are integral to contractility. Atrial dilation is a late feature of this fibrotic process, and greater accommodation of re-entry circuits is possible through progressively increased atrial size.…”

“…Pulmonary vein "PV" Ostia are the sources of ectopy and scar related substrates that initiate and promote AF. 8 The diameter of the PVs may play a pivotal role. 11 Hence, circumferential isolation of all PVs, has established itself as a mainstay of treatment for AF.…”