Introduction: Atrial flutter with 1:1 atrioventricular conduction is an arrhythmia that usually occurs when-class IC antiarrhythmic drugs are prescribed to patients with paroxysmal atrial fibrillation. In the absence of an-tiarrhythmic therapy, 1:1 atrioventricular conduction is a rare, but still possible condition. In this situation, aberrant conduction occurs, resulting in a wide QRS complexes tachycardia, which requires a differential diagnosis with a major impact on the subsequent treat-ment strategy.

Methods: We are presenting the case of a 46-year-old patient transferred from a local hospital, where he was admitted for an episode of palpitations accompanied by dizziness. A wide QRS complexes tachycardia was documented, being considered a ventricular tachycar-dia at the onset of an acute coronary syndrome, due to the isolated increase of T troponine. Antiarrhythmic treatment with Amiodarone was started achieving thus rate control, with passage in 2:1 atrioventricular con-ducted flutter.

Results: On admission, the patient has rhythmic cardi-ac sounds, he is in sinus rhythm 76 / min with narrow QRS complexes. Repeated episodes of paroxysmal atri-al fibrillation occurred initially, which responded to intravenous Metoprolol. Subsequently, the recurren-ce of the large QRS complexes tachycardia occurred, with haemodynamic compromise, which required the administration of an 50J electric shock, with restorati-on of sinus rhythm. The ventricular activation time is very short and it indicates the supraventricular origin of the wide QRS complexes tachycardia, which turns out to be an atrial flutter with 1:1 atrioventricular con-duction and a right bundle branch aberrant conduc-tion morphology, an other argument being the recent history of 2:1 atrioventricular conducted atrial flutter. Echocardiography was normal, except the presence of a normofunctional bicuspid aortic valve. The electrophy-siological study showed a hyperconducting atrioventri-cular node (AH 40 ms, HV 44 ms), and radiofrequency ablation of the cavot-tricuspid isthmus was performed, with a bi-directional block at the end of the procedu-re. An accessory pathway was excluded. On discharge, anticoagulant treatment was started, with no antiarrhytmic. After three months, the patient maintains si-nus rhythm without antiarrhythmic and anticoagulant treatment.

Conclusions: The atrial flutter with 1:1 atrioventricular conduction was the primary documented arrhythmia of this patient, which was treated successfully. The asso-ciation between 1: 1atrioventricular conducted flutter and aortic bicuspid aortic valve is most likely random, especially in the young patient, when the aortic valve, although bicuspid, is normofunctional and there is no hemodynamic impact of bicuspidia. This case illustra-tes the coexistence of atrial flutter with 1: 1 atrioventri-cular conduction and aortic bicuspid valve in a young patient without previous antiarrhythmic medication and a hyperconductingatrioventricular node. On the other hand, it emphasizes the importance of differenti-al diagnosis of wide QRS complexes tachycardia.