Abstract
We encountered a case of a one-year-old girl who was diagnosed with focal atrial tachycardia (FAT) at two months old. The FAT was controlled with medical treatment. However, she later developed pallor and tachycardia, with a heart rate of 180 beats per minute (bpm). This occurred after an acute onset of high-grade fever for four days, followed by rapid fever reduction and a rash. She exhibited signs of chest discomfort by grabbing her clothes around her chest and complaining of chest pain. On the second day after the fever subsided, she suddenly became pale with tachycardia and was brought to our emergency department. A 12-lead electrocardiogram (ECG) revealed a sinus rhythm of approximately 120 bpm with frequent nonsustained FAT. Initial laboratory investigations showed normal results: creatinine kinase at 99 IU/L, troponin T at 0.010 ng/mL, and an elevated B-type natriuretic peptide level at 95.1 pg/mL. Echocardiography revealed a pericardial effusion of up to 6.6 mm despite normal cardiac function. We clinically diagnosed her with acute pericarditis and administered aspirin. The pericardial effusion resolved after two weeks but recurred two months later. Prednisolone was administered for recurrent pericarditis, and aspirin was replaced with colchicine. After one month, the pericardial effusion was resolved, and the prednisolone was discontinued. Subsequent echocardiography showed no pericardial effusion and no evidence of diastolic dysfunction. The quantitative polymerase chain reaction confirmed the presence of human herpesvirus 6 (HHV-6) in her serum at the onset of the disease. Additionally, serologic tests conducted in acute and chronic phases indicated viral antibody titers that were eight and 256 times higher, respectively. In conclusion, the HHV-6 virus can cause acute viral pericarditis in patients with exanthema subitum.