Does size still matter? The prognostic significance of left atrial shape in catheter ablation of atrial fibrillation

Introduction

As early as the 1970s, left atrial (LA) geometry was recognized as a mechanistically important factor in the development of atrial fibrillation (AF). Whilst quantitative assessment was limited to crude echocardiographic measurements of LA diameter as a marker of dilatation, it represented a valuable tool in risk stratification and patient selection for treatments such as electrical cardioversion (1).

Following these initial observations, the concept of “AF begets AF” became a key component in our understanding of its pathophysiology (2). Experimental evidence demonstrated that sustained AF had structural effects on the myocardium, leading to increase in atrial cell size and overall atrial dilation. In turn, a dilated atria had a greater propensity to sustain AF (3,4).

Contemporarily, catheter ablation is a key tool in our arsenal for managing AF. Guidelines emphasize the importance of patient selection, with consideration given to risk of recurrence (5). Variables such as age, sex, and nature of AF are established risk factors (6,7) and common to multiple scoring systems designed to aid the clinician (DR-FLASH, ATLAS, CAAP-AF)(5). Yet our regard of LA geometry remains simplified, with LA diameter >40-47mm the metric used in the majority of these risk calculators (5).

Our understanding of the correlation of LA geometry with AF risk has progressed significantly in recent years. More sophisticated echocardiographic techniques and cross-sectional imaging with CT and MRI have improved our ability to accurately capture raw geometry. Alongside improvements in the computer sciences, we can now analyse not only LA size through LA diameter or LA volume, but LA shape using entirely novel metrics (table). Here, I will discuss three in more detail and use each to highlight a possible explanation for why LA deformation is anisotropic.