A single atrial extrastimulus during a short RP tachycardia

Abstract

A 26-year-old female underwent electrophysiological study for recurrent palpitations. She was in sinus rhythm at baseline with cycle length (CL), atrial-His (AH), and His-ventricular (HV) intervals of 802, 87, and 48 ms, respectively. Ventricular pacing showed decremental ventriculoatrial (VA) conduction with concentric atrial activation. Parahisian pacing showed VA prolongation with loss of His capture consistent with nodal conduction. Rapid atrial pacing induced a short RP tachycardia with a CL of 580 ms that corresponded to the tachycardia documented clinically (Figure 1). The VA interval was 30 ms during the tachycardia with the earliest atrial activation at the proximal coronary sinus. The short VA interval is not consistent with atrioventricular reentrant tachycardia, but atrial tachycardia (AT), atrioventricular nodal reentrant tachycardia (AVNRT), and junctional tachycardia (JT) are possible differential diagnoses. During tachycardia, a single premature atrial complex (PAC) was introduced from the proximal coronary sinus (Figure 2). Based on the response to the extra stimulus, what is the most likely mechanism of the tachycardia? Commentary The short RP tachycardia with a very short VA interval can represent AT with a long atrioventricular (AV) delay, typical slow-fast AVNRT, or JT. Although JT is an uncommon tachycardia mechanism in this setting, it becomes a distinct possibility due to the long CL of the tachycardia.