Atrial Flutter with Spontaneous 1:1 Atrioventricular Conduction in Adults: An Uncommon but Frequently Missed Cause for Syncope/Presyncope


  • Conflict of interest: None declared.

Address for reprints: Gioia Turitto, M.D., F.A.C.C., Cardiac Electrophysiology Services, New York Methodist Hospital-Cornell Heart Center, 506 Six Street, Brooklyn, NY 11215. Fax: 718-780-7717; e-mail:


Aims: To compare patients with atrial flutter (AFl) and 1:1 atrioventricular conduction (AVC) with patients with AFl and higher AVC.

Methods: The characteristics of 19 patients with AFl and 1:1 AVC (group A) were compared with those of 116 consecutive patients with AFl and 2:1 AVC or higher degree AV block (group B).

Results: Age, gender, and left ventricular function were similar in the two groups. In group A versus group B, more patients had no structural heart disease (42% vs 17%, P < 0.05) and syncope/presyncope (90% vs 12%, P < 0.05). The AFl cycle length (CL) in group A was longer than in group B (265 ± 24 ms vs 241 ± 26 ms, P < 0.01). The transition from AFl with 1:1 to 2:1 AVC or vice versa was associated with small but definite changes in AFl CL, which showed larger variations in response to sympathetic stimulation. In group A patients who were studied off drugs, the atrial-His interval was not different from group B, but maximal atrial pacing rate with 1:1 AVC was faster. In group A, five patients were misdiagnosed as ventricular tachyarrhythmias, and three with a defibrillator received inappropriate shocks. Four patients had ablation of AVC and six had ablation of AFl circuit.

Conclusions: The main difference between groups A and B may be an inherent capacity of the AV node for faster conduction, especially in response to increased sympathetic tone. The latter affects not only AVC but also the AFl CL. One should be aware of the different presentations of AFl with 1:1 AVC to avoid misdiagnosis/mismanagement and to consider the diagnosis in patients with narrow or wide QRS tachycardia and rates above 220/min.