3 DISCUSSION
LA thrombus, a common cause of cerebral infarction, is caused by conditions involving blood stagnation in the left atrium. It has been reported that 93.6% of patients who develop LA thrombus have atrial fibrillation and 88.7% have concomitant mitral valve disease.1, 2 Other causes of LA thrombus are low left ventricular function, large left atrium, bradycardia, and congenital hypercoagulability. However, cases without AF or mitral regurgitation are extremely rare.
The reason for the formation of large LA thrombus in this case is unclear. Echocardiography showed no mitral valve disease or low left ventricular function. The left atrial diameter was within the normal range (37 mm). He had no bradycardia. Blood tests revealed that the anti-thrombin Ⅲ level was within the normal range (99%), and the fibrinogen level was slightly elevated (493 mg/dL) probably because of the preoperative mesh infection. Congenital coagulopathy could be a differential diagnosis, but no significant past medical history of significant coagulopathy or family history was found. He had started taking oral anticoagulants after the surgery; hence, detailed blood tests for coagulation, including protein C and protein S, were unavailable. Some reports have reported that the patent foramen ovale causes LA thrombus, but only when the thrombus extends from the right atrium through the patent foramen ovale into the left atrium, which is not consistent with the present case. 3 The remaining possibility was that the small LA tumor triggered the formation of a thrombus, but no obvious tumor component was detected on pathological examination. During hospitalization, he had sinus rhythm and no subjective symptoms, but some possibility of paroxysmal atrial fibrillation existed; hence, a more detailed evaluation, including Holter electrocardiography, was required. Furthermore, infection and dehydration are known to trigger thrombus formation. It is likely that the mesh infection temporarily increased coagulability and dehydration caused by fasting accelerated thrombus formation.
Cardiac tumors in the left atrium are mostly benign, with half of them being myxoma and the other half being lipoma or papillary fibroelastoma. It is often difficult to distinguish between LA tumors and LA thrombi on echocardiography. Myxomas appear with a smooth surface, usually are attached to the atrial septum by the stalk in the fossa ovalis and could present inhomogeneous areas of hyperechogenicity due to calcification. Contrarily, thrombi have frequently homogenous, and are usually found in the left atrial appendage.4 Contrast echocardiography has been reported as a way to distinguish between thrombi and myxomas,5 and may be an option for further evaluation to differentiate between them.
Early surgical resection is recommended for large LA thrombi. Leung et al. reported that patients with LA thrombus have an embolism risk of 10.4% per year and a mortality rate of 15.8% per year.6 In patients with small thrombus size, small left atrial diameter, and fresh thrombus, anticoagulation therapy may be effective against LA thrombus; 7 Surgical resection is required if the aforementioned conditions are not met. Mobile thrombi are considered to have a higher risk of embolism 8 and may require early surgery. It also has been reported that the average time between the diagnosis of LA thrombus by echocardiography and the onset of embolism is 53 days. 7 If the patient is elderly or otherwise at high surgical risk, anticoagulation should be attempted if LA thrombus is suspected; however, if anticoagulation is found to be ineffective, surgical resection should be considered as early as possible. In this case, based on the size of the thrombus and the presence of calcification, anticoagulation was probably ineffective. Fortunately, the patient was cured with early surgery without embolism. We believe that predicting the risk of embolization and the effect of anticoagulation therapy based on the characteristics of the thrombus and if required, early surgical intervention can prevent thrombosis and improve patient’s prognosis.