P0405 - Rapidly Growing Left Atrial Thrombus Unexpectedly Found Two Months After Heart Transplant in a 10-Year-Old Female.

Background Left atrial (LA) thrombus is occasionally encountered in post heart transplant patients. Pathogenesis is poorly understood. Multiple factors are considered, including left atrial enlargement, coagulation abnormality, hemodynamic abnormality, atrial arrhythmia, transplant rejection, and steroid use. Anticoagulation therapy and surgical excision are the main treatment options. A decision may be challenging given that the definitive diagnosis requires pathologic evaluation of the mass.
Case Presentation Ten-year-old female underwent orthotropic heart transplant for severe genetic dilated cardiomyopathy. The patient was discharged home on post-operative day 28 after uneventful clinical course. The third endomyocardial biopsy, 9 days prior to this presentation, demonstrated acute cellular rejection (ACR) grade 2R, for which she was admitted for intravenous steroids for 3 days (methylprednisolone 10 mg/kg/day) and discharged home on tapering oral steroids along with her regular immunosuppressive therapy. On her follow up visit, five days after discharge, routine echocardiogram identified an echogenic mass in the left atrium (Figure 1). Mass was presumed to be thrombus given its absence on the echocardiogram five days prior. On examination, she was well-appearing with normal neurological examination. The patient was admitted to the cardiac intensive care unit for further management. Complete blood count was unremarkable. Blood culture was sent for possible endocarditis. Patient was started on intravenous heparin infusion and empiric antibiotics. Given the thromboembolic risk, the patient underwent surgical resection of the LA mass on the third hospital day. The mass was attached to interatrial septum approximately 3-4 mm above the mitral valve. Postoperative course was unremarkable. Pathological specimen showed 1.5 x 1 cm sized mass consistent with thrombus (Figure 2). Hypercoagulable workup was only significant for MTHFR heterozygous C677T and heterozygous A1298C mutations with normal homocysteine level.
Conclusion Several cases have reported LA thrombus after heart transplant with variable pathogenesis, mostly with atrial fibrillation or low cardiac output status. Our patient had no arrhythmia and normal systolic function. However, it is plausible that high dose steroid use in ACR and MTHFR mutation contribute to LA thrombus formation. In most of the reported cases, intracardiac thrombus was detected years after heart transplant with insidious course. In our case, however, LA thrombus was discovered only 2 months after heart transplant with a rapid progression over 5 days. This highlights the importance of surveillance echocardiograms in post-transplant patients.