Change in atrial activation patterns during narrow complex tachycardia: What is the mechanism?

A change in the coronary sinus (CS) activation pattern from an eccentric to a concentric pattern during the ablation of an orthodromic reciprocating tachycardia might falsely suggest the presence of a second (septal) accessory pathway (AP) during tachycardia or the successful ablation of the left lateral AP under ventricular pacing despite persistent and unaffected AP conduction. Complete or partial intra-atrial block should be suspected when an abrupt change in the atrial activation sequence is noted during catheter ablation at the posterolateral and lateral aspects of the mitral annulus. The correct anatomical position of the CS catheter plays a vital role in the differential diagnosis of this situation

An interesting response to His-synchronous ventricular stimulation: What is the mechanism of this supraventricular tachycardia?

A20‐year‐old male with an implantable cardioverter‐defibrillator(ICD) that had been implanted 7 years ago due to recurrent and failedablation for fascicular left ventricular tachycardia was referred forseveral inappropriate shocks and an elective replacement indicatoralert. He had no personal or family history of sudden cardiac death orinherited disorders that can cause arrhythmia