An 89 year-old man presented after being found down at home. His history included hypertension and hyperlipidemia. His exam was notable for an irregularly irregular rhythm at a rate of 150 beats per minute. EKG showed new coarse atrial fibrillation which was rate controlled with metoprolol prior to his spontaneous conversion to sinus rhythm. Trans-thoracic echocardiography revealed a large, lobulated, homogeneous mass affixed to the posterior wall of the right atrium, measuring 3.8 cm x 1.7 cm, whose appearance was most consistent with thrombus. The echocardiogram did not show evidence of pulmonary hypertension or elevated right-sided pressures. The patient was started on therapeutic anticoagulation with heparin. During the subsequent week he remained hemodynamically stable. A repeat echocardiogram performed 6 days after the initial study showed resolution of the previous right atrial mass. He was discharged in stable condition to continue anticoagulation as an outpatient.
Right atrial thrombi are far less common than their left atrial counterparts. Much as in the left atrium, right atrial thrombi are prone to form in the setting of atrial fibrillation albeit at a significantly reduced rate. A posited explanation for this finding is the differing anatomy of the right and left atrial appendages, the portions of the atria most likely to provide a nidus for thrombosis. The right atrial appendage, being considerably more shallow than the left, provides a less hospitable environment for thrombus formation. Indeed, right atrial appendage thrombi are found in 3% to 6% of patients with atrial fibrillation while left atrial thrombi are found in 13% of the same population. Additionally, patients with right atrial thrombi most typically have concomitant left atrial thrombi, further suggesting that, given the anatomy of the right atrium, clots on the right require a more thrombogenic milieu to form. Right atrial thrombi are more common than left atrial thrombi in the setting of in-dwelling catheters, with clots most often forming at or near the catheter tip adjoining the junction of the SVC and RA. Additionally, deep venous thrombi may be caught in the right atrium while on their way to the lungs, a phenomenon referred to as “thrombus in transit”. In a meta-analysis of 119 patients with pulmonary embolism and residual clot found in the right atrium at the time of evaluation, the mortality rate was 80 – 100% in untreated patients compared to 30% in treated patients. The rates of thromboembolic events and mortality are still not well established in cases of right atrial thrombus without concomitant pulmonary embolism.
Right atrial thrombosis is significantly less common than left atrial thrombosis due to the anatomic differences between the atria and their appendages. Right atrial thrombi may sometimes represent residual clot from PE. Pulmonary embolism with residual right atrial thrombus has a high rate of morbidity and mortality and may be treated with anticoagulation in the stable patient while requiring emergent thrombolysis or thrombectomy in the unstable patient.
To cite this abstract:Naymagon L, Carney K, Fagan I. Right Atrial Thrombus. Abstract published at Hospital Medicine 2016, March 6-9, San Diego, Calif. Abstract 708. Journal of Hospital Medicine. 2016; 11 (suppl 1). https://www.shmabstracts.com/abstract/right-atrial-thrombus/. Accessed April 4, 2020.