A 13-year-old football player with a 1-year history of recurrent palpitations during exercise despite beta-blocker therapy attended our Paediatric Arrhythmia Clinic. An initial electrophysiology study diagnosed typical slow-fast AVNRT. Despite an aggressive radiofrequency ablation procedure including lesions in the low, middle, and superior aspects of the triangle of Koch as well as in the coronary sinus, we could not induce any junctional response. After a conventional right-sided procedure, there was no modification in the tachycardia characteristics or in the slow pathway conduction (including tachycardia induction, cycle length, and slow pathway refractory period). A decision was made to attempt a left-sided procedure.
A steerable decapolar electrode catheter was placed in the coronary sinus, and the His position was again identified on the anterior septum. The transseptal puncture was performed using the usual technique under fluoroscopy guidance without complications, followed by heparin administration. A deflectable catheter with a 4-mm tip was introduced into the left atrium, and the septal aspect of the mitral valve was mapped. A balanced atrioventricular signal with multicomponent atrial electrograms and low amplitude potentials was identified in the posteroseptal aspect of the mitral annulus, 3 mm above the coronary sinus (Figure 1). This left site clearly corresponded with the usual target for a conventional right-sided procedure (Figure 2, Figure 3). At this point, a single radiofrequency application resulted in an immediate accelerated junctional response with stable retrograde ventriculoatrial conduction. This application also resulted in temperatures of 55 -60  and was continued for 60 seconds. After this ablation, AVNRT was not inducible despite aggressive atrial stimulation on isoprenaline. The procedure was terminated without complications, and the patient did not show recurrence of palpitations afterward.