CT Imaging to Assess the Left Atrial Appendage Anatomy: Clinical Implications

Abstract

The left atrial appendage (LAA) is a highly complex anatomical structure distinct from the rest of the left atrium from an embryologic, anatomic, and pathophysiologic standpoint. While the LAA is a remnant of the embryonic left atrium, the remaining of the left atrial cavity derives from an outgrowth of the pulmonary veins. From a pathophysiologic perspective, the LAA is not just an embryologic remnant. Rather, it plays a significant role in the thromboembolic risk associated with atrial fibrillation, and is a demonstrated trigger site of atrial tachyarrhythmias. Moreover, LAA regulates normal cardiac physiology through functional receptors that influence heart rate, and secretes natriuretic peptides in response to change in left atrial pressure. In recent years, the study of LAA anatomy and its relationship with surrounding structures has gained increasing interest, as transcatheter techniques of LAA exclusion and radiofrequency ablation of left atrial tachyarrhythmias have been increasingly implemented. Multidetector computerized tomography (CT), with its capability to distinguish among small density differences in structures attenuation, is emerging as the noninvasive reference test to image the LAA and define its anatomy and topographic relationships. This chapter will review the role of CT to image the LAA, discussing the clinical implications different LAA morphologies detected at CT imaging.