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Thrombus or Bilobar Left Atrial Appendage? Diagnosis by Real-Time Three-Dimensional Transesophageal Echocardiography

Mizuguchi, K Annette MD, PhD*; Burch, Thomas M. MD; Bulwer, Bernard E. MD; Fox, Amanda A. MD*; Rizzo, Robert J. MD§; Shernan, Stanton K. MD*

doi: 10.1213/ane.0b013e3181857e53
Cardiovascular Anesthesiology: Echo Rounds
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From the *Department of Anesthesiology, Perioperative and Pain Medicine, Harvard Medical School, Brigham and Women’s Hospital, Boston, Massachusetts; †Department of Anesthesiology, Perioperative and Pain Medicine, Children’s Hospital Boston and Harvard Medical School, Boston, Massachusetts; ‡Cardiovascular Division, Harvard Medical School, Brigham and Women’s Hospital, Boston, Massachusetts; and §Department of Cardiac Surgery, Harvard Medical School, Brigham and Women’s Hospital, Boston, Massachusetts.

This article has supplementary material on the Web site:www.anesthesia-analgesia.org.

Accepted for publication May 20, 2008.

Reprints will not be available from the author.

Address correspondence to K. Annette Mizuguchi, MD, PhD, Department of Anesthesiology, The Brigham and Women’s Hospital, Perioperative and Pain Medicine, 75 Francis St., Boston, MA 02215. Address e-mail to amizuguchi@partners.org.

An 84-yr-old man, with a history of severe aortic stenosis (AS) and chronic atrial fibrillation treated with chronic warfarin therapy, presented with acute shortness of breath, elevated troponin levels and inferolateral ischemic changes on his electrocardiogram. A transthoracic echocardiogram revealed severe AS, mild aortic regurgitation, severe mitral regurgitation, moderate tricuspid regurgitation, and preserved left ventricular (LV) function. Cardiac catheterization demonstrated three-vessel coronary artery disease. He was subsequently taken to the operating room for coronary artery bypass grafting (CABG), aortic valve replacement, and mitral valve replacement (MVR).

Intraoperative transesophageal echocardiogram (TEE) confirmed the preoperative transthoracic echocardiogram findings by demonstrating severe mitral regurgitation with isolated flail of the middle posterior leaflet scallop, severe AS, a normal LV, and an enlarged left atrium (LA) with spontaneous echo contrast. In addition, routine two-dimensional (2D) TEE evaluation of the left atrial appendage (LAA) revealed a 0.6 × 1.6 cm mobile density consistent with a thrombus-like mass (Fig. 1; Video clip; please see video clip available at www.anesthesia-analgesia.org). The LAA Doppler flow velocity was variable due to atrial fibrillation, ranging from 20 to 35 cm/s. Further evaluation with a real-time 3-D Matrix TEE transducer (RT-m3D; Phillips Healthcare, Andover, MA) revealed a bilobar (bifid) LAA with a well-defined septum, but no evidence of thrombus (Fig. 2; Video clip). After the distal anastomoses for the CABG, the surgeon performed a left atriotomy in preparation for a MVR and confirmed the presence of a bilobar LAA without thrombus. The surgeon subsequently replaced the aortic valve and completed the proximal anastomoses for the CABG. The patient was successfully weaned from cardiopulmonary bypass and subsequently discharged from the hospital on postoperative day 55, after a prolonged hospital course complicated by heparin-induced thrombocytopenia.

Figure 1

Figure 1

Figure 2

Figure 2

The LAA forms jointly from the left wall of the primordial LA and pulmonary vein during the third week of gestation.1 It is typically described as a tubular, hooked structure with a relatively narrow neck and pectinate muscles confined to the body of the LAA. An autopsy study of 500 normal human hearts noted that the LAA was multi-lobed and the presence of 2 lobes (54%) was the most frequent, followed by 3 lobes (23%), 1 lobe (20%), and 4 lobes (3%).2

The LAA may be a major source of cardiogenic thrombus formation. TEE is considered the “gold standard” diagnostic tool for diagnosing a LAA thrombus, which typically appears as an independently mobile echogenic mass with well defined borders.3 Additional echocardiographic features that support the diagnosis of LAA thrombi include the presence of spontaneous echo contrast, enlarged LA, and reduced LV ejection fraction. In addition, in a study of 500 patients, LAA pulse wave Doppler flow velocities <20 cm/s were associated with an incidence of thrombus in 29% of patients, whereas a cutoff value of 55 cm/s had a high negative predictive value.4 Thus, in our case, even though the LAA flow velocities were variable, values ranged from <20 cm/s to 35 cm/s, thrombus could not be excluded.

The complex 3D anatomy of the LAA can make diagnosis of thrombi difficult. Prominent pectinate muscles, the presence of severe spontaneous echo contrast, and multiple lobes can make interpretation of LAA anatomy challenging by 2D TEE alone. Additionally, the “coumadin ridge” or “warfarin ridge,” which is a normal ridge of tissue that separates the LAA from the left upper pulmonary vein, may be associated with acoustic shadowing that can be mistaken for a thrombus or a mass. Traditional 3D echocardiographic reconstruction can provide excellent visualization of the LAA.5 However, prolonged image acquisition and reconstruction times, along with a requirement for electrocardiogram and respiratory gating, may limit its practical value. The recent introduction of a RT-m3D TEE transducer permits virtually instantaneous 3D imaging while preserving spatial and temporal resolution, thereby significantly enhancing the visualization of complex 3D structures as the LAA (Fig. 3).6

Figure 3

Figure 3

In this particular case, although real-time intraoperative 3D TEE was useful for differentiating a congenital bilobar LAA from a pathological thrombus, its direct impact on surgical decision making may seem to be limited, since this patient was already scheduled for a MVR, and the surgeon was, therefore, committed to inspecting the LAA. Nonetheless, considering the relatively common incidence of this congenital variant, and the difficulty in differentiating LAA lobar septa from thrombus using 2D TEE alone, when confronted with a similar diagnostic dilemma in a patient not scheduled for LAA exploration, RT-m3D may provide additional important diagnostic information to the intraoperative echocardiographer, thereby preventing the incorrect recommendation for an unnecessary surgical intervention.

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