Figure 49-1. A, Drawing of a left atrial appendage (LAA) anatomic specimen consisting of three lobes. Each protrusion from the body comprises a separate lobe. Directional changes or bends in the tail do not usually comprise new lobes. B, LAA with two lobes (1 and 2). C, Measurements of the LAA in a gross pathologic specimen. The echocardiographic orifice (Oe) is larger than the anatomic orifice (Oa). The length (L) of the appendage is a curvilinear distance (dashed line) from Oa to the tip of the tail, whereas the maximal width (W) is a straight-line measurement. Almost all appendages in the adult contain pectinate muscles greater than 1 mm in diameter. Oe is usually measured from the junction of the left superior pulmonary vein (LSPV) as it enters the left atrium (LA) to the junction of the LA and LAA. LIPV, left inferior pulmonary vein; LPA, left pulmonary artery. (From Veinot JP, Harrity PJ, Gentile F, et al: Anatomy of the normal left atrial appendage: A quantitative study of age-related changes in 500 autopsy hearts. Implications for echocardiographic examination. Circulation 1997;96:3112-3115.)
in 42% of hearts, extremely bent and slightly spiraled in 24%, slightly bent and extremely spiraled in 5%, and slightly bent and spiraled in 23%. Fifty-six percent had more than five branches (orifice area, >10 mm2), and 47% had more than 40 "twigs" (orifice area, 1-10 mm2). The mean minimal and maximal orifice diameters were 15 and 21 mm, respectively. Mean length (bottom to top) was 30 mm, mean width was 21 mm (at right angles), and mean volume was 5220 mm3 (5.22 mL).16 Blood supply to the LAA is typically provided by the left circumflex or right coronary arteries from positions in the left and right atrioventricular sulci.17
The microscopic appearance of the LAA in patients with chronic AF has been compared with that in patients with sinus rhythm.18 Patients with AF generally exhibit marked fibrous endocardial thickening and a much smoother internal LAA surface. It is unclear whether the LAA endocardium resembles the remainder of the heart in structure and function,19 although LAA myocardial cells are visually similar to those in other parts of the heart.20 The LAA epicardial thickness is greater for those portions overlying the ventricles.
Morphologic changes occur in the LAA after exposure to ionizing radiation. Generalized collagen (fibrosis) develops in rat hearts exposed to radiation, with reduction of appendage volume and loss of elasticity. These changes appear to negatively influence ventricular function,21 because evidence suggests that the LAA plays a role in LV filling and contributes to normal cardiac function.22-25
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