A 50-year-old woman was referred to our hospital for catheter ablation of a regular narrow QRS tachycardia with a short RP interval. In an electrophysiological study, the baseline atrio-His (AH) and His-ventricular intervals were normal. Retrograde conduction during ventricular pacing was decremental and concentric with the earliest atrial activation site (EAS) at the ostium of the coronary sinus (CS). No retrograde dual atrioventricular (AV) nodal physiology was observed. A narrow QRS tachycardia was reproducibly induced by programmed atrial extrastimuli with an AH interval jump.

The electrocardiogram-based algorithm for predicting para-septal atrial tachycardia (PSAT) is limited by the significant overlaps in the P-wave morphology originating from various para-septal sites.

A 70-year-old man underwent an electrophysiology study for episodic palpitations. The baseline HV interval was 54 ms. Atrial extrastimulus testing induced a short RP tachycardia initiated by prolongation of the AH interval. The response of the tachycardia to ventricular overdrive pacing (VOP) from the right ventricular (RV) apex is shown in Figure 1A, and the response to atrial overdrive pacing is shown in Figure 1B. Ventricular premature depolarizations (VPDs) delivered during His bundle (HB) refractoriness resulted in a repetitive response (Figure 2).

Atriofascicular fibers (AFFs) are rare accessory pathways that have higher rates of recurrence after ablation because of either failure to identify AFF (M) potentials or mechanical termination with contact.