Differentiating atrioventricular nodal re-entrant tachycardia from junctional tachycardia: conflicting reponses?

Typical atrioventricular nodal re-entrant tachycardia (AVNRT) is the most common supraventricular tachycardia; however, junctional tachycardia (JT) is rare and occurs mostly in children or during infusion of isoproterenol.1,2 Distinguishing between these arrhythmias can often be challenging during electrophysiology testing. They share many common characteristics, including similar intracardiac activation patterns, similar sites of earliest activation, and typical occurrence of a His bundle deflection before the atrial and ventricular electrograms. Slow pathway (SP) modification has evolved as the first-line treatment for AVNRT with acute success rates of 95% to 98%3,4; however, catheter ablation of JT has lower success rates and a higher rate of atrioventricular block.5 Previous studies have suggested that premature atrial contractions (PACs) or atrial overdrive pacing can rapidly differentiate AVNRT from JT.2,6 Editor’s Perspective see p 236 A 72-year-old woman with a history of paroxysmal supraventricular tachycardia that was refractory to medical therapy underwent catheter ablation. During the procedure, baseline AA interval during sinus rhythm, AH interval, and HV interval were 610, 80, and 38 ms (Figure 1A), respectively. Narrow QRS tachycardia was induced by atrial burst pacing (320 ms; Figure 1B), which was felt to be most consistent with slow/fast AVNRT (cycle length, 380 ms; AH, 340 ms; HA, 40 ms) based on the characteristics of induction with a critically long AH interval and the response to right ventricular overdrive pacing (Figure 1B and 1C). SP modification was performed and guided by intracardiac electrograms and fluoroscopic landmarks. After SP modification, a tachycardia spontaneously initiated during infusion of isoproterenol …