Left Atrial Thrombus

The risk factors identified with intra-cardiac thrombus formation include abnormal endocardium, loss of atrial contraction, arrhythmias and abnormal dilatation of cardiac chambers. Endocardial endothelium functions as a structural and functional barrier between the blood and highly thrombogenic subendothelial tissue. Abnormal and turbulent flow patterns cause endothelial injury and dysfunction leading to increase incidence of thromboembolism. Arrhythmias, particularly atrial fibrillation and enlargement of one or more cardiac chambers without apparent structural damage have an increase incidence of thromboembolic events [1]. Left atrial thrombus almost always origin from the extreme posterior wall of the left atrium and is also identified as the MacCallum’s patch, which was first described by MacCallum in 1924. This region macroscopically appears as a map like area which contains thickened, wrinkled and roughened part of endothelium [2]. Transesophageal echocardiography is believed to be the most sensitive method of detecting intracardiac thrombi although it is relatively invasive. Spontaneous echo contrast (SEC) in an ultrasound phenomenon, which indicates hypercoagulable or pre thrombotic state and is associated with increased risk for thromboembolic complications. Ultrasound reflection of normal blood is too low to produce an image and appear anechoic. Contrast enhanced CT scans or cardiac CT angiograms demonstrate a thrombus as a filling defect. However SEC caused by slow blood flow can cause an apparent filling defect simulating a thrombus. This pseudo filling effect on CT is due to incomplete mixing of CT contrast material in early, single phase contrast enhanced studies. Two phase cardiac CT angiography had shown a high sensitivity and a negative predictive value in assessing a cardiac thrombus. The late phase images depict a true thrombus as a persistent filling defect in the late phase [3]. A left atrial thrombus has to be differentiated from an atrial myxoma which is also commonly involve the left atrium. Atrial myxomas are benign cardiac neoplasms that commonly arise from interatrial septum. They and be sessile or pedunculated and shows variable contrast enhancement. Thrombi almost always arise from left atrial appendage, they are usually sessile and do not demonstrate contrast enhancement [4].