Introduction: Atrial tachyarrhythmias are common in patients with congenital heart disease, especially after reparative surgical procedures. Several studies show-ed that these patients have an increased risk of sudden cardiac death. Atrial arrhythmias are associated with a 50% increase in mortality and a two-fold increased risk of heart failure or stroke. Moreover, rhythm disturban-ces are characterized by antiarrhythmic drug resistance and a lower rate of successful ablations in this patient population.

Methods: We present the case of a 46 year old patient with a history of tricuspid valve endocarditis secondary to a perimembranous ventricular septal defect, where surgical correction of the VSD and tricuspid anulo-plasty were performed. T he patient presented recur-rent typical and atypical atrial flutter episodes, which did not respond to drug therapy, followed by syncope. Taking into account the arrythmias drug resistance, an electrophysiological study was performed. Initially, entrainment pacing was performed which located the macroreentrant circuit in the right atrium. The anato-mical and voltage map performed with a high density mapping catheter (Pentaray – Biosense Webster) de-termined the scar tissue on the lateral wall of the right atrium. The activation and propagation maps showed a double-loop reentry atrial flutter which used the atrio-tomy scar as well as the cavo-tricuspid isthmus. Initi-ally, radiofrequency energy was delivered at the cavo-tricuspid isthmus. Despite the successful cavo-tricus-pid isthmus block the tachycardia continued.

Results: The activation map obtained with the help of the high density catheter correctly determined the scar related macro-reentrant atrial circuit. Radiofrequency energy was applied to an isthmus of slow-conduction of the scar which terminated the arrhythmia. Differen-tial pacing was then performed in order to confirm the continuity of the ablation lines.

Conclusions: Atrial tachyarrithmias have a strong im-pact on morbidity and mortality in patients with con-genital heart disease. Radiofrequency ablation guided by a high denisty mapping catheter is highly useful in treating these arrythmias, but the succes rate is lower and recurrence rate higher than in the general popu-lation.