The left atrial appendage (LAA) has a key role in the embolic complications of atrial fibrillation (AF). It has been studied extensively, from recent interest in the thrombotic implications of various LAA morphologies to LAA occlusion and ablation. We collected eleven post-mortem LAA samples for visual analysis, two were not included due to poor sample quality. On examination of the nine remaining samples, several common patterns of pectinate muscle orientation were noted. The LAA samples were noted to have a smooth circumferential neck of muscular tissue giving rise to a dominant singular smooth trunk of papillary muscle in 7 cases and two trunks in 2 cases. These trunks were either shallow (5 samples) or more muscular and raised (4 samples). Shallow trunks tended to be wider than the raised trunks and may even be circumferential (2 samples). The main trunk arborised to give off papillary muscle branches down to third or fourth order branches. The samples were visually assessed for the percentage of smooth papillary muscle versus non-papillary recesses and were found to have 50% smooth muscle in 3 samples, 50-75% in 3 samples and >75% in 3 samples. We performed histological analysis of further LAA samples collected during cardiac surgery in a parallel study. We identified a distinct pattern of myocyte orientation from the neck, mid-section and apical section of the LAA demonstrating arborisation of myocyte fibres with minimal communication in distal segments of the LAA. We hypothesize that this information could be used to develop a specific LAA ablation strategy for persistent AF. If the ostium of the LAA was ablated in a near-circumferential pattern leaving only a small gap in line with the predominant myocardial trunk then this could organize LAA activity with potential amelioration of its roles in the maintenance of persistent AF and in thrombostasis.
Credits: Dr Mark Hensey , Dr Louisa O’Neill, Dr Ciara Mahon, Dr Aurelie Fabre, Prof. David Keane , Stephen Keane