Conventional Approach To Cardioversion Of Atrial Fibrillation

Although no prospective, randomized studies have been performed to determine the optimal INR or duration of precardioversion warfarin, historical data suggested 3-4 wk of warfarin (INR 2.0-3.0) before elective cardioversion is sufficient. The use of this "conservative" strategy comes at the "cost" of a delay in cardioversion for the vast majority of patients who could otherwise undergo early and safe cardioversion. This 1-mo delay exposes the patient to prolonged precardioversion warfarin therapy (with associated risk of hemorrhagic complications) and prolongs the period of AF before cardioversion. It has been estimated that up to a quarter of patients receiving warfarin in preparation for cardioversion do not undergo the initially scheduled cardioversion because of hemorrhagic complications and/or a transient subtherapeutic INR. For patients with hemorrhagic complications, the clinician is faced with the difficult choice of reducing the intensity of anticoagulation, often to a subtherapeutic range (with the patient remaining in AF). For the patient with a transient subtherapeutic INR, the dose of warfarin is increased, and the "1-mo clock" must be restarted. Finally, the use of 1 mo of precardioversion warfarin serves to prolong the duration of AF before cardioversion, and thus adversely impacts the rate of recovery of atrial mechanical function and long-term maintenance of sinus rhythm. The impact on atrial function and long-term maintenance of sinus rhythm appears to be most relevant for those presenting with AF of only several weeks duration.

ANATOMICAL AND FUNCTIONAL CONSIDERATIONS IN TRANSESOPHAGEAL ECHOCARDIOGRAPHY: THE LAA

Understanding LAA anatomy is essential for interpretation of transesophageal echocardiography (TEE) findings. Its morphology is complex and highly variable. The LAA receives more attention than the right appendage in AF as it is (by far) the preferred site for thrombus formation. Its anatomical configuration—the narrow neck and multiple ridges—may promote thrombus formation in pathological states.

Topographical Relationships and External Anatomy

The LAA is an irregularly-shaped tubular expansion arising from the antero-lateral corner of left atrium (Fig. 1). Its external surface appears lobulated and forms part of the cardiac silhouette on chest radiographs. Antero-medial to the LAA lies the root of the pulmonary artery. Inferiorly, it sits above the short left main coronary artery as it bifurcates into the left anterior descending and left circumflex vessels, and the great cardiac vein, which flows into the coronary sinus. Laterally, the LAA is covered by parietal pericardium that abuts the adjacent pleura and lung.

Internal Morphology

The luminal surface of the LAA exhibits a varied array of ridges formed by the pectinate muscles (comblike arrangement of cardiac muscle fibers) that line its floor and lateral walls (Fig. 2). The pectinate muscles commence distal to its distinct neck or waist that delineates it from the rest of the smooth-walled left atrium. Their appearance on TEE (Fig. 3A; please see companion DVD for corresponding video) must be appreciated and distinguished from artifact and thrombi (Fig. 3B-D [please see companion DVD for corresponding video] and Table 3). Familiarity with normal LAA morphology on TEE is perhaps the best way to distinguish between artifact, pectinate muscles, and thrombi.

The maximal internal length of the LAA is measured along a curvilinear line reflecting its curved tubular anatomy, but additional lobes and appendage orientation are commonly seen on TEE (Fig. 4). Necropsy resin casts have shown LAA dimensions to range from a 16 mm to 51 mm along its curvilinear length, and 5 to 40 mm

Pectinate Muscles

Left lateral

Fig. 1. Frontal and left lateral views of the heart showing the left atrial appendage.

Left lateral

Fig. 1. Frontal and left lateral views of the heart showing the left atrial appendage.

Left atrial appendage internal

Left atrial appendage internal

Left Atrial Appendage Anatomy
Fig. 2. Composite images showing the internal morphology of the left atrial appendage and pectinate muscles on transesphageal echocardiography.

in diameter measured at its neck. The area of the appendage measured on two-dimensional TEE in a small series of 117 patients averaged 3.7 cm.

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