A case of atrial fibrillation complicated by complete atrioventricular block.

Atrial fibrillation and complete atrioventricular block are two well-established arrhythmias that can share common aetiologies and risk factors. Although the two arrhythmias can co-exist, only a limited number of cases of atrial fibrillation complicated by complete atrioventricular block have been reported. Correct recognition is essential due to the risk of sudden cardiac death. A 78-year-old female with known atrial fibrillation presented with a 1-week history of shortness of breath, chest tightness and dizziness. On assessment, she was bradycardic with a heart rate of 38 bpm, despite the absence of any rate-limiting medication. Electrocardiography revealed an absence of P waves with a regular ventricular rhythm, consistent with a diagnosis of atrial fibrillation complicated by complete atrioventricular block. This case highlights the diagnostic electrocardiography features of co-existing atrial fibrillation with complete atrioventricular block that are often misinterpreted, leading to a delay in correct diagnosis and initiation of definitive management. Upon diagnosis, it is essential to exclude the reversible causes of complete atrioventricular block before considering permanent pacing. In particular, this includes rate-limiting medications in patients with pre-existing arrhythmias such as atrial fibrillation and electrolyte disturbances.