Ruptured Membrane of the Left Atrial Appendage.

A 75-year-old woman with newly diagnosed atrial fibrillation was referred for cardioversion. She was a smoker and had hypertension that she controlled with medications. Her renal function, electrolyte levels (including potassium and magnesium), and thyroid-stimulating hormone levels were within normal limits. The results of a recent transthoracic echocardiogram, which she had undergone as an outpatient, were within normal limits. We started her on a regimen of anticoagulation with dabigatran and performed transesophageal echocardiography (TEE), with plans for electrical cardioversion if no left atrial appendage (LAA) thrombus was found.The TEE showed no evidence of an LAA thombus, but there was a thin membrane extending across the ostium of the LAA, with a hypermobile, hyperechoic structure attached to it (Fig. 1). We considered that this lesion could be a dehisced segment of the membrane itself or an attached thrombus. Color-Doppler mode showed blood flow through the apparently ruptured membrane (Fig. 2). However, we aborted electrical cardioversion for fear that a thrombus was attached to the membrane.Fig. 1Transesophageal echocardiogram (mid-esophageal short-axis view at the level of the aortic valve) shows a dehisced membrane (arrow) with a mobile component extending across the ostium of the left atrial appendage.Fig. 2Transesophageal echocardiogram in color-flow Doppler mode (mid-esophageal short-axis view at the level of the aortic valve) shows flow across the dehisced membrane of the left atrial appendage.