How Can a Large Left Atrial Myxoma Cause a Selective Mid-Diastolic Right-to-Left Atrial Shunt?

Abstract

A 76-YEAR-OLD MAN was admitted to the authors’ institution for evaluation of syncope. The patient suffered a witnessed, brief (15 to 20 seconds) loss of consciousness after standing up from a seated position in his home. The patient’s wife called emergency medical services. The patient had no neurologic deficits or other injuries related to the fall, but persistent hypotension was observed in the emergency department that was unresponsive to volume administration. An intravenous infusion of dopamine was required to increase his arterial blood pressure to the normal range. The patient anecdotally reported gradually worsening dyspnea on exertion, lower extremity swelling, and modest weight gain. The past medical history was notable for atrial fibrillation, which was first recognized 1 week before the current admission; treatment with digoxin and furosemide was begun at that time. Transthoracic echocardiography was performed as part of the diagnostic evaluation and revealed a 7.6×4.0 cm smooth, highly mobile mass with a broad-based pedicle attachment to the atrial septum that prolapsed through the mitral valve into the left ventricle during diastole. Computed tomography verified these findings. The imaging studies suggested that the mass was most likely a left atrial myxoma. The patient suffered another episode of near-syncope in the hospital during which, his wife reported, he “turned blue.” He spontaneously recovered after assuming a recumbent position. The patient subsequently was transported to the operating room for resection of the presumed myxoma. After anesthetic induction and endotracheal intubation, transesophageal echocardiography (TEE) confirmed the preoperative diagnosis (Fig 1, Fig 2, Fig 3). The left ventricle was relatively underfilled and the right ventricle was markedly dilated (Fig 4). A pulmonary artery catheter was inserted. Central venous and mean pulmonary arterial pressures were elevated (average values of 28 and 36 mmHg, respectively) despite administration of an intravenous infusion of milrinone. An atrial right-to-left shunt tracking along the mass’s anterior-superior surface was observed during mid-diastole (Fig 5). The shunt was absent throughout the remainder of the cardiac cycle. Two additional images were obtained (Fig 6, Fig 7). What is the diagnosis? Fig 2Midesophageal four-chamber transesophageal echocardiography view obtained during systole showing large left atrial mass occupying the majority of the left atrium. View Large Image Figure Viewer Download Hi-res image Fig 3Midesophageal four-chamber transesophageal echocardiography view obtained during mid-diastole showing large left atrial mass prolapsing through the mitral valve into the left ventricle. View Large Image Figure Viewer Download Hi-res image Fig 4Midesophageal transgastric short-axis transesophageal echocardiography view obtained at end-diastole showing marked right ventricular dilatation. View Large Image Figure Viewer Download Hi-res image Fig 5Modified midesophageal aortic valve short-axis color Doppler transesophageal echocardiography view obtained during mid-diastole showing a right-to-left atrial shunt (red) tracking along the anterior-superior border of the left atrial mass. View Large Image Figure Viewer Download Hi-res image Fig 6Modified midesophageal aortic valve short-axis transesophageal echocardiography view obtained during early diastole showing deformation of the anterior atrial septum (white arrow) by the movement of the left atrial mass. View Large Image Figure Viewer Download Hi-res image Fig 7Modified midesophageal aortic valve short-axis transesophageal echocardiography view obtained during mid-diastole showing transient opening in the anterior atrial septum (white arrow) as a result of deformation by movement of the left atrial mass. View Large Image Figure Viewer Download Hi-res image