Architecture of atrial musculature in humans.

Abstract

Objective-To investigate the gross arrangement of the principal muscular bundles of the two atria, and to suggest how it may contribute to contraction and spread of atrial excitation. Design-A prospective analysis based on anatomical examination of adult human hearts. Setting-A national heart and lung institute and a tertiary referral centre for cardiac disease. Material-9 normal postmortem human hearts. Methods-Dissection of atrial muscles with macrophotography. Results-The atrial walls consist of circumferential and longitudinal muscular bundles, the former being arranged at the base of the atria with the latter predominating in the parietal walls. The muscular bundles in the right atrium are larger than those in the left. The main muscles forming the right atrial wall are the terminal crest and terminal pectinate muscles. The terminal crest, the most obvious muscle, is arranged longitudinally with its pectinate muscles connecting to the musculature of the atrioventricular vestibule. No structure resembling the terminal crest is seen in the left atrium. Instead the left atrial wall is composed of intermingled series of muscles, chief of these being the interatrial band and the septoatrial bundle. The former is arranged circumferentially at the atrial base, while the latter is mainly longitudinal. The wall of the right atrium is not of uniform thickness because of the presence of the terminal crest and its pectinate muscles on its internal surface. By contrast, the left atrial wall is much more uniform and its average thickness is greater than that of the right atrium. The rim of the oval fossa is the most important muscular structure on the septal surface and is formed by the infolded atrial walls. The other principal muscles of the atria attach to it, so that the rim provides mechanical support for overall movement of the atrial walls. Comparison of the gross arrangement of the atrial musculature with earlier echocardiographic measurements showed that this arrangement of the muscle explains movement of the atrioventricular ring and overall atrial contraction, and provides a suitable substrate for preferential conduction. Conclusion-The anatomical features of the atrial musculature explain the known facts concerning atrial contraction and preferential conduction. (Br HeartJ7 1995;73:559-565)

Conduction Velocity around the Tricuspid Valve Annulus during Typical Atrial Flutter by Electro‐anatomic Mapping System

“…17) A correlation was observed between parallel versus perpendicular fiber orientation with respect to the TA and fast versus slow conduction in the triangle-of-Koch. These observations of myocardial fiber anisotropy in the triangle-of-Koch [17][18][19] are consistent with the observations from this study and may account for the fact that the slowest conduction in the AFL circuit is in areas of the septal isthmus.…”

Anatomic characteristics of left atrium and openings of pulmonary veins

“…It originated on the anteroinferior margin of the septum and then passed to the anterior base of the atrium. This band attached to the leaflet of mitral ring (12). This location of septal band was the same as described in present study.…”

“…They explained that extensions of atrial myocardium onto pulmonary veins and superior vena cava were common (7). Wang et al (12) used nine normal postmortem human hearts to explain architecture of atrial musculature. They described the left septoatrial bundle as a flattened muscle seen internally.…”

Quantitative assessment of the left atrial myocardial deformation in patients with chronic mitral regurgitation by strain and strain rate imaging: an observational study

“…Unlike LV, the atrial walls have a unique contraction/relaxation cycle due to having longitudinal and circumferential muscle bundles arranged in a complex manner (8). Atrial mechanical cycle is consisted of three phases: reservoir phase (RP) during LV systole, conduit phase (CP) during early and mid-period of the ventricular diastole, and pump phase (PP) which enhance LV filling during late diastole (9)(10)(11).…”