Cardiovascular Anesthesiology: Echo Rounds
An 86-yr-old women was transferred to our institution with new onset, left-sided weakness and a diagnosis of an acute myocardial infarction. Her medical history was significant for hypertension, stroke, and atrial fibrillation. The patient's warfarin therapy had been discontinued secondary to a history of bleeding complications. A heparin infusion was initiated and transthoracic echocardiography (TTE) revealed a left atrial mass that appeared adherent to the atrial septum. A subsequent cardiac catheterization demonstrated a mobile left atrial mass and nonobstructive coronary artery disease. A second TTE confirmed a mobile 3 × 3 cm left atrial mass that periodically obstructed the mitral valve (MV) (Fig. 1A, Video Clip 1; please see video clips available at www.anesthesia-analgesia.org). The MV apparatus was structurally normal with no regurgitation or valvular stenosis; the remainder of the TTE examination was unremarkable, with no mass noted in the left atrial appendage (LAA). The patient was scheduled for urgent surgery. Induction, tracheal intubation, and central venous line insertion (using ultrasound) were conducted in the reverse Trendelenburg position because of the dynamic nature of the mass and the extent to which it obstructed the MV. A transesophageal echocardiography (TEE) probe was placed and the initial opening four-chamber view did not demonstrate an intracardiac mass (Fig. 1B, Video Clip 2; please see video clips available at www.anesthesia-analgesia.org). There was concern the mass had fragmented and embolized. On further examination, the atrial mass was found to have lodged in the LAA (Fig. 1C, Video Clip 3; please see video clips available at www.anesthesia-analgesia.org). A right thoracotomy was performed, followed by initiation of cardiopulmonary bypass and left atriotomy. A 3.5 × 2.0 × 1.0 cm ovoid mass was removed and characterized as thrombus by pathological evaluation.
Examination of the LAA is critical in the evaluation of a possible thrombus. The LAA can be imaged by TEE in the horizontal midesophageal short-axis view at the base of the heart (30–60°) and the two-chamber midesophageal longitudinal view (90°).1 A multiplane probe rotating stepwise around the cavity (0–180°) improves assessment. Clots may remain hidden because of the three-dimensional complexity of the LAA; 80% of LAA have been reported to be multilobed and 50% bilobular. Tissue Doppler imaging and the use of contrast may be helpful if imaging is difficult or inconclusive, and three-dimensional TEE holds future promise. Timing of the perioperative examination is critical, and can change the proposed surgical procedure if the thrombus is noted to have embolized; thus, TEE should be performed preincision if possible.2
Patients at risk of developing left atrial thrombi are those with conditions predisposing to low-flow states. Atrial fibrillation, left atrial enlargement, and MV stenosis are associated with stasis and thrombus formation. The observation of spontaneous echo contrast in the left atrium on echocardiography has been identified as a risk factor for thrombus formation.3 The presentation of a patient with an atrial ball thrombus can include syncope, pulmonary congestion, stroke, or sudden death from a ball-valve effect. Thrombi may fragment and embolize, causing limb ischemia, a myocardial infarction or disruption of the systemic circulation. Echocardiographic characterization of the mass can stratify embolic risk; mobile-ball type thrombi embolize more frequently than fixed-ball or mountain-type masses.4
Changes in body position can adversely affect the erratic kinetics of the mass within the left atrium. Patients in the sitting or left lateral decubitus position have minimal movement of the thrombus, thus preventing obstruction of the MV. Patients in the supine or right lateral decubitus have demonstrated frequent bouncing of the thrombus into the MV, occasionally causing obstruction.5 In this case, we maintained a reverse Trendelenburg position throughout induction and central line placement. This positioning may have contributed to the entry of the thrombus into the LAA, but was deemed critical to minimize the risk of systemic embolization or MV obstruction.
Atrial thrombus treatment recommendations include urgent surgical intervention, oral and IV anticoagulation and the use of intraatrial thrombolytics. It is possible that the thrombus in this patient had decreased in size as a result of heparin infusion, which has been shown to have a fibrinolytic effect via inhibition of plasminogen activator inhibitor-1.6 Thus, a diminished thrombus possibly settled and/or returned to the LAA, although fragmentation and embolization could also explain the reduction in size.
We conclude that a TEE examination, including a thorough evaluation of the LAA, is a critical component of the perioperative management of a patient with suspected atrial thrombus. Such patients should be treated with caution, including particular attention to patient positioning throughout management to minimize the risk of embolization.
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