Abstract
Background:
Third-degree atrioventricular (AV) block, or complete heart block, is a severe cardiac conduction abnormality characterized by complete dissociation between atrial and ventricular activity. While commonly associated with structural heart disease and advanced age, it may also arise from multiple reversible and irreversible contributors, creating a complex diagnostic challenge.
Case Presentation:
An 85-year-old male with a history of atrial fibrillation and prior coronary artery bypass grafting presented with generalized weakness, bradycardia, and dyspnea. Vital signs revealed profound bradycardia at 34 beats per minute with preserved hemodynamic stability. Laboratory evaluation demonstrated severe hyponatremia, markedly elevated cardiac biomarkers, elevated liver enzymes, creatine kinase, and thyroid dysfunction. Electrocardiogram confirmed third-degree AV block with atrioventricular dissociation and ventricular escape rhythm. The patient had recently initiated a sleep medication, representing a potential pharmacologic contributor. Despite initial stability, cardiology was emergently consulted, and the patient was transferred for permanent pacemaker placement.
Discussion:
Complete heart block often results from a multifactorial interplay of conditions, including electrolyte abnormalities, endocrine dysfunction, and medication effects, which may unmask underlying conduction disease. Reversible causes such as hyponatremia and hypothyroidism can impair conduction but are frequently insufficient as sole explanations in elderly patients. Notably, patients may remain hemodynamically stable despite severe bradycardia due to compensatory mechanisms, potentially delaying recognition and treatment. Early electrocardiographic identification, prompt cardiology consultation, and definitive management with pacemaker implantation are critical to prevent rapid clinical deterioration.
