Atrial flutter with 1:1 conduction in a 70-year-old man with hyperthyroidism.

Atrial flutter (AFL) is a rapid, regular atrial tachyarrhythmia that occurs most commonly in patients with underlying structural heart disease. AFL with 1:1 atrioventricular (AV) conduction is a rare occasion. We describe a 70-year-old male patient with hyperthyroidism in whom AFL was associated with 1:1 AV conduction. This case report emphasizes that AFL with 1:1 AV conduction should be kept in mind as a diagnostic alternative in patients with rapid supraventricular tachycardia and hyperthyroidism.