The Hidden Cost of Immunity: Myocarditis Presenting as Complete Heart Block in an Older Adult Following COVID-19 Booster.

BACKGROUND: Myocarditis has been rarely reported following COVID-19 vaccination, most commonly in younger males. Although a temporal association has been observed, establishing causality in individual cases remains challenging. Myocardial inflammation may involve the cardiac conduction system, rarely resulting in high-grade atrioventricular (AV) block. Importantly, these conduction abnormalities may be transient and resolve as the underlying inflammation improves. CASE SUMMARY: We report a rare case of myocarditis following a COVID-19 vaccination in an elderly woman who experienced complete heart block and worsening exertional dyspnea subsequent to receiving a COVID-19 booster. Coronary angiography revealed patent coronary arteries, and magnetic resonance imaging confirmed the presence of myocarditis. Her conduction abnormality progressively resolved without the need for permanent pacing, and she was subsequently discharged in stable condition. DISCUSSION: Myocarditis should be considered as a potentially reversible cause of high-grade AV block. A thorough clinical history and multimodal imaging are essential for diagnosis, as early recognition and appropriate monitoring may allow recovery of AV conduction and avoid unnecessary permanent pacemaker implantation.