File:PMC3034459 ipej100556-01.png

English: F1: Basal ECG (A): atrial tachycardia with 2:1 conduction is detectable. The atrial waves morphology (negative in lateral leads - see black arrow - and positive in V1) involves the likely diagnosis of left sided atrial tachycardia. Intracardiac electrograms (B) show left atrial tachycardia (cycle length 300 msec) with 2:1 conduction to the ventricles; the distal dipole of the catheter positioned inside the coronary sinus is the first one to be recording atrial signals, thus suggesting a left lateral origin of the tachycardia. The registration speed is 100 mm/sec. Post-procedural surface ECG (C): sinus rhythm is visible. Intracardiac electrograms (D) confirm the earliest atrial activation to be at the level of the high right atrium (HRA). Map d = distal dipole of the ablation catheter. Map p = proximal dipole of the ablation catheter. DCS = distal dipole of the catheter in coronary sinus. HRA = catheter positioned at the level of the high right atrium