An Elusive Case of Transient 6:1 High-Grade Atrioventricular Block Despite Normal Initial Testing

We present a case of a 55-year-old man with a prior history of syncope and vertigo due to high-grade atrioventricular (AV) block despite initial negative tests. The patient underwent multiple diagnostic evaluations, including a normal echocardiogram, myocardial perfusion imaging, Holter monitoring, and electrocardiography. As his symptoms continued to persist, an implantable loop recorder (Confirm Rx™; Abbott, Sylmar, USA) was inserted subcutaneously, which revealed transient 6:1 high-grade AV block and bradycardia. Despite normal initial investigations, his persistent symptoms and documented conduction abnormality prompted pacemaker (Abbott, Sylmar, USA) placement. This case highlights the importance of detailed electrophysiologic assessment and close monitoring in patients with recurrent unexplained syncope and high-grade AV block, even with prior normal testing.