Background Atrial flutter with 1:1 (AFL 1:1) conduction may be spontaneous or secondary to anti-arrhythmic drug (AAD) use. This group of patients are not well characterised. We aimed to compare various characteristics between patients suffering 'spontaneous' AFL 1:1 (the development of 1:1 Atrioventricular conducting Atrial Flutter in the absence of concomitant AAD use) and 'Drug-induced' AFL 1:1.

Methods This is a retrospective study of patients referred to our institution over an 8 year period. Sixty-eight patients had confirmed and documented atrial flutter with 1:1 conduction.

Results Baseline clinical characteristics and differences between the study populations are summarised in Table.

Patients with spontaneous AFL 1:1 had a significantly higher flutter rate and were less likely to have concomitant AF. Drug-induced AFL 1:1 was mainly secondary to Class 1 AAD's despite the use of AV blocking agents in a third of these patients. Sixty-three patients underwent a successful cavotricuspid isthmus ablation with no recurrence.

Conclusions We have reported the largest series of patients with atrial flutter and 1:1 conduction. Patients suffering spontaneous AFL 1:1 had a significantly faster flutter rate compared to the drug-induced population.