A 22-year-old woman with hypertension and end-stage renal disease was referred for a transthoracic echocardiogram to evaluate cardiac function. The study revealed normal chamber sizes and left ventricular systolic function; however, an unusual turbulence was noted on color-flow Doppler in the left atrium, originating adjacent to the anterior mitral valve leaflet base. A transesophageal echocardiogram, obtained for better characterization of this jet, showed a linear echogenic structure extending across the orifice of the left atrial appendage (LAA) (Fig. 1). Biplane and 3-dimensional full-volume images revealed a thin membrane (Fig. 2) that substantially decreased the cross-sectional area of the orifice as compared with that of the body of the LAA (0.57 vs 1.78 cm2) (Figs. 3 and 4). A to-and-fro turbulent, high-velocity jet at the level of this orifice was consistent with restriction of blood flow into and out of the LAA (Fig. 5). These findings were consistent with a fenestrated congenital membrane of the LAA. Of note, the LAA was free of thrombus.
Left atrial appendage membrane is an extremely rare, congenital variant of LAA anatomy. Reported only a handful of times, similar membranous partitions of the appendage have been described as obstructive (at the mouth of the appendage) and nonobstructive (within the body). The clinical significance of this entity is currently unknown. It is possible that the obstructive subgroup increases the likelihood of LAA thrombus development, especially in patients with atrial fibrillation or flutter. Conversely, these membranes might decrease the chance of clot embolization by decreasing the cross-sectional area of the LAA orifice.1 The LAA, with its substantial distensibility, might serve as a decompression chamber that positively influences left atrial pressure and volume relationships. Thus, an LAA membrane could adversely affect the hemodynamic modulation of left atrial pressure, promoting atrial arrhythmogenesis.2,3 An increased prevalence of atrial arrhythmias in the presence of LAA membranes has been described, but given the small sample size, the causal association remains unclear. More widespread recognition of this entity might aid in understanding the clinical implications, if any, of this rare congenital anomaly.
Section Editor: Raymond F. Stainback, MD, Department of Adult Cardiology, Texas Heart Institute, 6624 Fannin St., Suite 2480, Houston, TX 77030
From: Division of Cardiovascular Medicine, Department of Internal Medicine, Harper Hospital, Wayne State University School of Medicine, Detroit, Michigan 48201
Dr. Alesh is now at the Division of Cardiovascular Medicine, Department of Internal Medicine, St. Bernardine Medical Center, University of California, Riverside, California.