Left atrial appendage: anatomy and imaging landmarks pertinent to percutaneous transcatheter occlusion

Left Atrial Appendage Exclusion for Atrial Fibrillation

“…It is differentiated from the pulmonary vein-derived smooth-walled cavity of the remaining left atrium by rich endocardial trabeculations formed by parallel-running muscle bars, termed pectinate muscles. 15 The LAA ostium is separated from the left superior pulmonary vein by a narrow tissue invagination (the left lateral ridge) 16 in which lies the ligament of Marshall, a developmental remnant of the left-sided vena cava of importance in AF arrhythmogenesis. 17, 18 The left lateral ridge clearly defines the superoposterior border of the LAA ostium endocardially, seen as a “q-tip” on echocardiography, with the other borders being less well defined.…”

“…19 In approximately 30% of individuals, muscular trabeculations can be found extending inferiorly from the appendage to the vestibule of the mitral valve. 16 The muscular architecture of the LAA is complex, with overlapping cardiomyocytes of different orientations, and is invested by extensions of Bachmann’s bundle which bifurcate around the LAA neck, with contributions from the septopulmonary and septoatrial bundles. 16, 20 In dogs, the epicardial LAA tip is the last to activate 21 although similar human data is lacking.…”

“…15, 16, 19 It rests freely within the confines of the pericardial sac with the left phrenic nerve having a variable superimposed course as part of the pericardiophrenic neurovascular bundle. 26, 27 The ostium shares important relationships with the left superior pulmonary vein endocardially and the coronary vessels epicardially, with the left aortic sinus and main coronary artery lying posterior and medial, and the great cardiac vein and circumflex artery lying inferior.…”

“…28 The left anterior descending artery runs underneath the body, emerging at a point immediately below the LAA tip, although the tip’s position can vary. 16 In a minority of patients, the sinus node artery arising from the circumflex artery runs nearby 19 and can assume an S-shape as it courses between the LAA and left superior pulmonary vein. 16 …”

CT imaging for left atrial appendage closure: A review and pictorial essay

“…may be at risk from device deployment include the left circumflex artery, the sinoatrial nodal artery where this arises from the left circumflex artery, and the great cardiac vein and its tributaries. 8 The more anteriorly located left phrenic nerve also courses along the surface of the pericardium in close proximity to the base of the LAA and may be liable to injury, particularly with epicardial techniques for LAA occlusion. 7,8 In addition to the main LAA, up to 15% of the population may have accessory LAAs or diverticula, which may also potentially serve as a nidus for thrombus formation or interfere with catheter deployment and manipulation, particularly during AF ablation procedures where they may be mistaken for pulmonary vein ostia.…”