Ann Thorac Surg 2008;86:1011-1012. doi:10.1016/j.athoracsur.2008.02.099
© 2008 The Society of Thoracic Surgeons
Case Reports
Missing Left Atrial Thrombus: Dislodgement or Artifact?
Kazuhiro Kurisu, MD*,
Manabu Hisahara, MD,
Yusuke Ando, MD
Department of Cardiovascular Surgery, Kitakyushu Municipal Medical Center, Kitakyushu, Japan
Accepted for publication February 29, 2008.
* Address correspondence to Dr Kurisu, Department of Cardiovascular Surgery, Kitakyushu Municipal Medical Center, 2-1-1 Bashaku, Kokurakita-ku, Kitakyushu, 802-0077, Japan (Email: byou-iryou-cvs{at}city.kitakyushu.lg.jp).
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Abstract
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Patients with a left atrial thrombus are considered at high risk of thromboembolism. Surgical treatment is generally recommended. We experienced a case of a patient with a history of cerebral embolism related to chronic atrial fibrillation in whom, unexpectedly, no thrombi were found at thrombectomy. Although echocardiography is a useful method for detection of a thrombus in the left atrium, the possibility of a reverberation artifact should be routinely explored.
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Introduction
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Patients with chronic atrial fibrillation are susceptible to left atrial thrombus formation and are at potential risk of thromboembolism [1–4]. Transesophageal echocardiography is a useful method for detection of thrombi in the left atrium [2–4]. However, in some cases, an artifact mimicking a left atrial thrombus is recognized [3, 4]. We report the unexpected case of a patient with a mobile left atrial thrombus that was not detected at operation.
A 60-year-old man was referred to our hospital for treatment of a left atrial thrombus. He had a cerebral embolism 3.5 years ago; he was initially diagnosed as having chronic atrial fibrillation and had taken anti-platelet drugs. No neurologic abnormalities, apart from dysarthria, were identified on medical screening. A chest radiographic scan showed an almost normal heart shadow with a cardiothoracic ratio of 50%.
Electrocardiography showed an atrial fibrillation with a ventricular rate of 86/min. Transthoracic echocardiography showed preserved left ventricular function with an ejection fraction of 61% and trivial mitral regurgitation. The left atrial dimension was 47 mm on M-mode measurement. Multi-plane transesophageal echocardiography (Toshiba Aplio 80, Tokyo, Japan) with a 5-MHz transducer revealed a mobile 11 x 7 mm echodense mass in the left atrial appendage (Fig 1). Considering the history of cerebral embolism, this finding was likely to be a thrombus, although other possibilities could not be completely ruled out. We planned an urgent surgery that included thrombectomy and a maze operation.
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Fig 1. Preoperative transesophageal echocardiography shows an echodense mass (arrow) mimicking a thrombus in the left atrial appendage.
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The mass shadow seen before was also identified on intraoperative transesophageal echocardiography after the induction of anesthesia. The surgery was carried out through a conventional median sternotomy and full cardiopulmonary bypass with ascending aortic perfusion and bi-caval drainages. Intermittent antegrade and retrograde infusion of cold blood cardioplegia was used for myocardial protection. A standard left atrial incision through the interatrial groove was performed after aortic clamping. However, no mass lesions were found; neither was an inverted left atrial appendage. The endocardium in appendage was likely to be intact without any mural thrombi. An attempt to find the thrombus in the left ventricle or proximal aorta through an exploratory aortotomy failed. Closure of the aortotomy was followed by a left-sided maze operation, including the excision of the left atrial appendage [5]. All ablation lesions were done using irrigated bipolar or unipolar radiofrequency, or both, and cryothermy. After completion of the left atriotomy closure, the heart was re-perfused.
To rule out an embolism, arterial pulsations were felt immediately after the operation; neurologic and visceral screening was undertaken after awakening from anesthesia; and thereafter, evaluation of cerebral and systemic embolism by computed tomographic scanning was performed within several postoperative days. All these efforts resulted in the conclusion that the patient was free from any embolism. The patient had an uneventful postoperative course and was discharged from our hospital with maintenance of his sinus rhythm.
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Comment
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Patients with chronic atrial fibrillation are susceptible to thromboembolism related to left atrial thrombi [1–4]. Leung and associates [2] evaluated actual prognoses for patients found to have left atrial thrombus on transesophageal echocardiography and reported the embolic event rate to be 10.4% per year. Predictors of subsequent thromboembolism were identified as a maximal thrombus dimension (
15 mm), history of thromboembolism, and mobile thrombus [2]. Surgical thrombectomy has generally been recommended in cohorts of patients with these risk factors. We decided to undertake an urgent thrombectomy to avoid any subsequent embolic events, although there was also a concern regarding other pathology.
We were very surprised and even shocked that the left atrial thrombus was missing at surgery. An important question was thus raised, that is, whether the thrombus had disappeared or if it had never existed? Some patients with a left atrial thrombus embolized during the perioperative period [6, 7], and a case of a silent embolism are reported [6]. Such an unusual situation was not ruled out in this particular case, but we speculated that the thrombus shadow seen on echocardiography was in fact an artifact rather than an actual thrombus. Two reasons led to this speculation. One was the absence of any thrombi in the left atrial appendage on macroscopic or microscopic findings. The other was that our echocardiographic finding closely resembled the representative images of reverberation previously reported [3, 4]. Reverberation artifacts are reported to arise from the ridge between the appendage and the left pulmonary vein, and to localize precisely at twice the distance from the transducer to the ridge [3, 4]. The rotation of the transducer by at least 120° seems to be helpful for exclusion of such reverberation artifacts [4].
If it is suspected that a mass shadow is an artifact, but that a real thrombus can not be ruled out, the dilemma whether surgical intervention should be performed or not occurs. In this particular case, a history of cerebral embolism prompted us to undertake surgical intervention, but surgery might not be recommended if a definite diagnosis of an artifact could be established. Although in some cases there is a disagreement regarding the diagnosing of a left atrial thrombus, even among experienced cardiologists [4], we should be concerned about the possibility of reverberation artifacts before undertaking intervention.
In conclusion, we experienced a case of an apparent left atrial thrombus that was found to be absent at surgery. The possibility of reverberation artifacts should be routinely explored to lessen the chances of unnecessary surgical interventions when a left atrial appendage thrombus is suspected by echocardiography.
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References
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- Gage BF, van Walraven C, Pearce L, et al. Selecting patients with atrial fibrillation for anticoagulation: stroke risk stratification in patients taking aspirin Circulation 2004;110:2287-2292.[Abstract/Free Full Text]
- Leung DY, Davidson PM, Cranney GB, Walsh WF. Thromboembolic risks of left atrial thrombus detected by transesophageal echocardiogram Am J Cardiol 1997;79:626-629.[Medline]
- Maltagliati A, Pepi M, Tamborini G, et al. Usefulness of multiplane transesophageal echocardiography in the recognition of artifacts and normal anatomical variants that may mimic left atrial thrombi in patients with atrial fibrillation Ital Heart J 2003;4:797-802.[Medline]
- Schneider B, Stöllberger C, Schneider B. Diagnosis of left atrial appendage thrombi by multiplane transesophageal echocardiography: interlaboratory comparative study Circ J 2007;71:122-125.[Medline]
- Gillinov AM, Blackstone EH, McCarthy PM. Atrial fibrillation: current surgical options and their assessment Ann Thorac Surg 2002;74:2210-2217.[Abstract/Free Full Text]
- Cecconi M, Manfrin M, Moraca A, et al. Silent embolism of a large pedunculated left atrial thrombus Ital Heart J 2002;3:199-201.[Medline]
- Ha JW, Chung N, Hong YW, Kwak YR, Chang BC, Cho SY. Alteration of surgical management following intraoperative transesophageal echocardiography in a patient with mobile left atrial thrombi embolized during anesthesia Echocardiography 2003;20:291-292.[Medline]
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Abstract
Introduction
