Atrial-His-atrial and atrial-His-His-atrial responses during slow-fast atrioventricular nodal reentrant tachycardia

Key Teaching Points•Atrial overdrive pacing (AOD) is useful in differentiating slow–fast atrioventricular nodal reentrant tachycardia (AVNRT) from junctional tachycardia (JT). Slow-fast AVNRT usually exhibits an atrial-His-atrial (AHA) response, whereas JT exhibits an atrial-His-His-atrial (AHHA) response.•An AHHA response is possible in slow-fast AVNRT with a double ventricular response.•In slow-fast AVNRT with a double ventricular response, the anatomical relationship between the pacing site and the entrance of the slow conduction (slow pathway) may contribute to the different responses to AOD. •Atrial overdrive pacing (AOD) is useful in differentiating slow–fast atrioventricular nodal reentrant tachycardia (AVNRT) from junctional tachycardia (JT). Slow-fast AVNRT usually exhibits an atrial-His-atrial (AHA) response, whereas JT exhibits an atrial-His-His-atrial (AHHA) response.•An AHHA response is possible in slow-fast AVNRT with a double ventricular response.•In slow-fast AVNRT with a double ventricular response, the anatomical relationship between the pacing site and the entrance of the slow conduction (slow pathway) may contribute to the different responses to AOD. Distinguishing junctional tachycardia (JT) from slow-fast atrioventricular nodal reentrant tachycardia (AVNRT) is challenging during electrophysiologic testing. Both rhythms have similar intracardiac electrogram activation patterns and earliest atrial activation sites with catheter mapping. Atrial pacing at a rate slightly faster than the tachycardia cycle length (TCL) (ie, atrial overdrive pacing [AOP]) from the high right atrium (HRA) or the proximal coronary sinus (CS) during a tachycardia could quickly differentiate JT from AVNRT. Previously, JT was identified with an atrial-His-His-atrial (AHHA) response in 100% (8/8) of cases, whereas AVNRT was identified with an atrial-His-atrial (AHA) response in 100% (14/14) of cases.1Fan R. Tardos J.G. Almasry I. Barbera S. Rashba E.J. Iwai S. Novel use of atrial overdrive pacing to rapidly differentiate junctional tachycardia from atrioventricular nodal reentrant tachycardia.Heart Rhythm. 2011; 8: 840-844Abstract Full Text Full Text PDF PubMed Scopus (48) Google Scholar We present a rare case of slow-fast AVNRT, wherein the response to AOP from the HRA exhibited an AHHA response, whereas that from the proximal CS exhibited an AHA response. A 65-year-old man presented to the emergency department owing to repetitive episodes of palpitations. A 12-lead electrocardiogram showed a normal sinus rhythm, and a regular narrow QRS complex tachycardia was identified during the palpitations (Supplemental Figure 1). After the patient’s informed consent was obtained, an electrophysiological study and catheter ablation of the tachycardia were performed. Under local anesthesia, 4 electrode catheters were inserted into the femoral and brachial veins and positioned in the right atrial appendage, His bundle region, CS, and right ventricular apex (Supplemental Figure 2A). At baseline, the atrio-His (AH) and His-ventricular intervals were 72 and 41 ms, respectively. Dual atrioventricular nodal physiology was observed during programmed double atrial extrastimuli. Programmed ventricular stimulation exhibited decremental ventriculoatrial conduction with the earliest atrial activation site located on the His electrograms (Supplemental Figure 2B). Para-Hisian pacing showed a retrograde AV nodal pattern. After infusion of isoproterenol, supraventricular tachycardia with a fixed 1:1 AV relationship was induced by double atrial extrastimuli, revealing an AH jump (Supplemental Figure 2C). During the tachycardia, the AH and His-atrial intervals were 430 and 64 ms, respectively. The cycle length oscillations of <15 ms were observed during the tachycardia. The atrial activation sequence during the tachycardia was identical to that during right ventricular pacing. Premature ventricular complexes during His refractoriness did not perturb the tachycardia. After the right ventricular overdrive pacing, the first return electrogram resulted in a ventricular-atrial-ventricular response, but the TCL after the pacing became altered by the pacing; thus, we could not evaluate the postpacing interval. Instead, we confirmed that the atrial timing was perturbed after the transition zone. From those findings, the tachycardia was diagnosed as slow-fast AVNRT. However, the response to AOP from the HRA was an AHHA pattern (Figure 1A), whereas that from the proximal CS was an AHA pattern (Figure 1B). As described in the Discussion section, an AHHA pattern would be possible in slow-fast AVNRT with a double ventricular response. Thus, radiofrequency energy was applied to the slow pathway potentials in the posteroseptal region. With a gradual titration increase of the radiofrequency energy from 15 W to 30 W, a steady junctional rhythm was confirmed during the application. After antegrade slow pathway modification, any evidence of dual AV nodal physiology (absence of an AH jump or echo beat) with and without isoproterenol was absent. During the 6-month follow-up, there was no recurrence of any symptomatic arrhythmias. The response to AOP during the tachycardia is important to distinguish AVNRT from JT. We described a case of slow-fast AVNRT that exhibited AHHA and AHA responses to AOP from the HRA and proximal CS, respectively. Inconsistent results can mislead the diagnosis, and the underlying mechanism should be cleared to prevent unnecessary ablation. In principle, an AHHA response is observed in JT (Figure 2A), whereas an AHA response is observed in AVNRT (Figure 2B).1Fan R. Tardos J.G. Almasry I. Barbera S. Rashba E.J. Iwai S. Novel use of atrial overdrive pacing to rapidly differentiate junctional tachycardia from atrioventricular nodal reentrant tachycardia.Heart Rhythm. 2011; 8: 840-844Abstract Full Text Full Text PDF PubMed Scopus (48) Google Scholar Thus, the mechanism of why the slow-fast AVNRT exhibited an AHHA response should be explained. A double ventricular response resulting from simultaneous antegrade conduction over the fast and slow pathways of the AV node clears this phenomenon.2Kim S.S. Lal R. Ruffy R. Paroxysmal nonreentrant supraventricular tachycardia due to simultaneous fast and slow pathway conduction in dual atrioventricular node pathways.J Am Coll Cardiol. 1987; 10: 456-461Crossref PubMed Scopus (29) Google Scholar When the tachycardia terminates during AOP and the last atrial pacing simultaneously propagates over the fast and slow pathways (ie, double ventricular response), the last atrial paced beat can result in 2 His signals. When an antegrade conduction via a slow pathway could retrogradely activate the fast pathway and reinitiate the tachycardia, an AHHA response is observed even in AVNRT cases (Figure 2C).3Alasti M. Mirzaee S. Machado C. et al.Junctional ectopic tachycardia (JET).J Arrhythm. 2020; 36: 837-844Crossref PubMed Scopus (5) Google Scholar A previous study examining slow-fast AVNRT reported a different pacing site-dependent response in the His bundle potentials during AOP. An orthodromic capture of the atrial electrograms at the recording site of the His bundle was observed during AOP from the proximal CS in 5 of 7 (71%) patients, whereas an antidromic capture was observed during AOP from the HRA in 4 of 4 (100%),4Satoh M. Miyajima S. Koyama S. Ishiguro J. Okabe M. Orthodromic capture of the atrial electrogram during transient entrainment of atrioventricular nodal reentrant tachycardia.Circulation. 1993; 88: 2329-2336Crossref PubMed Scopus (31) Google Scholar probably because the proximal CS pacing penetrated more easily into the upstream of the slow conduction, compared to the HRA pacing. When the pacing exhibits manifest entrainment and orthodromic capture of the earliest activation site, the entrance of the slow conduction zone is located between the pacing site and earliest activation site.5Okumura K. Olshansky B. Henthorn R.W. Epstein A.E. Plumb V.J. Waldo A.L. Demonstration of the presence of slow conduction during sustained ventricular tachycardia in man: use of transient entrainment of the tachycardia.Circulation. 1987; 75: 369-378Crossref PubMed Scopus (129) Google Scholar Thus, in typical AVNRT, the entrance of the slow conduction zone (probably equivalent to the antegrade slow pathway) would be located between the proximal CS and His bundle regions (Figure 3). The pacing from the entrance side of the slow conduction zone would allow an orthodromic penetration (conduction via the antegrade slow pathway) of the last pacing impulse down to the His electrograms, resulting in an AHA response (Figure 3B). Conversely, an antidromic penetration (conduction via the antegrade fast pathway) from HRA pacing may terminate the tachycardia during AOP (Figure 3C). When the last atrial pacing propagates over the fast pathway alone, the tachycardia does not recur after AOP. However, when the last atrial pacing simultaneously propagates over the fast and slow pathways (ie, double ventricular response), the antegrade conduction via the slow pathway could retrogradely activate the fast pathway, restarting the tachycardia. In this situation, an AHHA response is observed, leading to the misdiagnosis of the rhythm as JT. An AHHA response after cessation of AOP was possible even in patients with slow-fast AVNRT. Tachycardia termination during AOP, simultaneous fast and slow pathway conduction (ie, double ventricular response) of the last pacing stimulus, and restarting the tachycardia are the possible mechanisms of this phenomenon. Although there may be individual variations, AOP from the entrance side of the slow conduction zone (the proximal CS in typical AVNRT) may be the most suitable pacing site to correctly activate the antegrade slow pathway without terminating the tachycardia.