Clinical Anatomy of the Left and Right Atrial Appendages in Humans: Comparative and Developmental Perspective

Human atrial chambers derive from distinct embryonic anlagens, the original embryonic atria gradually transforming into the so-called auricles, or atrial appendages. This study quantifies macroscopic variations in pectinate muscle architecture in human atrial appendages and evaluates their visualization using clinical imaging modalities. We examined 153 cadaveric donor hearts (103 specified sex: 61 female, 42 male; plus 50 unspecified), employing gross dissection, ex vivo micro-CT, histology, and in vivo clinical imaging (CT angiography, MRI, and transthoracic/transesophageal echocardiography). Left atrial appendage (LAA) morphologies (Wang classification) comprised chicken-wing (41%), cactus (23%), cauliflower (22%), and windsock (14%) types, with 11 ± 4 (mean ± SD) main pectinate muscles (length: 47 ± 16 mm). Right atrial appendage (RAA) pectinate muscle arrangements (Loukas classification) were dominated by type IV (41%), followed by types I/II (22%/20%), with 17 ± 4 muscles (length: 75 ± 17 mm); the RAAs were larger (p < 0.001) but showed lower muscle density (p = 0.007) than the LAAs. All modalities resolved main pectinate bundles, with angio-CT providing superior LAA detail; transesophageal echocardiography excelled for both sides. Precise atrial appendage morphology informs catheter ablation, pacing, and stroke risk stratification, bridging anatomical and clinical perspectives.