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.