When the Heart Stops Conducting: AV Block in Acute Rheumatic Fever

Acute rheumatic fever (ARF) is an autoimmune inflammatory complication that occurs following pharyngitis caused by group A B-hemolytic Streptococcus (GAS). Although ARF predominantly affects children aged 5–15 years, initial presentations in young adults pose significant diagnostic challenges because of atypical clinical manifestations and low clinical suspicion. Cardiac conduction abnormalities commonly manifest as first-degree atrioventricular (AV) block, whereas complete AV block is exceptionally rare. This case report describes ARF in a young adult presenting with first-degree AV block and subclinical carditis, accompanied by a structured review of rheumatic conduction abnormalities. A 22-year-old Indonesian woman presented to the emergency department with a one-week history of severe migratory polyarthralgia involving the lower extremities, resulting in difficulty walking. She reported an untreated episode of sore throat and fever four weeks before presentation. Initial 12-lead electrocardiography (ECG) demonstrated first-degree AV block, with a prolonged PR interval of 240 ms (0.24 seconds) and a heart rate of 84 beats/min. Laboratory investigations revealed elevated inflammatory markers, including an erythrocyte sedimentation rate (ESR) of 88 mm/h and a C-reactive protein (CRP) level of 14.34 mg/L, along with leukocytosis (11,200 cells/µL) and an elevated antistreptolysin O (ASO) antibody titer of 1:400. Transthoracic echocardiography revealed mild mitral regurgitation with a preserved left ventricular ejection fraction of 67%, consistent with subclinical carditis. The diagnosis of ARF was established using the 2015 revised Jones criteria, based on one major and three minor manifestations. Treatment with oral methylprednisolone (24 mg/day), acetaminophen, and a single intramuscular dose of benzathine penicillin G (1.2 million units) was followed by normalization of the PR interval to 160 ms (0.16 seconds) and resolution of symptoms within 72 hours. This case highlights the diagnostic significance of PR interval prolongation in young adults presenting with migratory joint symptoms and suspected ARF. Although first-degree AV block may accompany rheumatic carditis, it is not independently diagnostic of valvular involvement. Early recognition, appropriate cardiac evaluation, and timely treatment are essential for identifying cardiac manifestations and guiding the management of ARF.