Hidenobu Ashikawa

Earlier Activation of the Distal than the Proximal Site of the Coronary Sinus May Represent Retrograde Conduction Through AV Node: Significance of Recording of Far Distal Coronary Sinus

During retrograde conduction through an accessory pathway (AP) or the atrioventricular (AV) node, earlier activation of the distal recording site than a more proximal site of the coronary sinus (CS) generally indicates retrograde conduction via a distally located AP. Thus, after successful ablation of a left‐sided AP, if the distal CS recording site is activated earlier than a more proximal site retrogradely, it is considered to suggest—in the absence of His‐bundle recording or more frequently in the setting of poor recording of the low septal right atrial electrogram—a conduction via a second AP (located more distally), and not conduction via the AV node. Yet, we hypothesized that retrograde conduction through the AV node may activate the far distal site of the CS (CSD) earlier than a more proximal site, as the anterior atrial wavefront, coming retrogradely from the AV node and traveling along the anterior mitral annulus, could reach the CSD earlier than a more proximal site. To test this we studied 18 patients with intact retrograde conduction via the AV node, but without evidence of an AP. The CSD was recorded by means of a quadripolar catheter (interelectrode distance of 2–5 mm); retrograde activation sequence at the distal (CSD1–2) versus proximal (CSD3–4) bipolar recording site was determined during ventricular stimulation. In 12 of 18 patients the CSD1–2 recording site was activated 5–10 ms earlier than the CSD3–4 recording site, in 3 of 18 patients the CSD1–2 site was activated 5 ms later than the CSD3–4 site; in the remaining 3 patients both recording sites were depolarized simultaneously. The results indicate that the CSD was often depolarized earlier than a more proximal site by impulses that conducted to the atria retrogradely via the AV node while the quadripolar recording catheter was placed at the CSD. This observation, al‐ though not well documented previously, suggests that the sequence of retrograde atrial activation in the CS should be studied carefully in consideration of the actual location of the mapping catheter in order to correctly diagnose the presence or absence of conduction via an AP.

Atypical Form of the Fourth Criterion for Transient Entrainment

The typical fourth criterion for transient entrainment is defined when both a sudden shortening in conduction interval to and a distinct change in electrogram morphology at a bipolar recording site are demonstrated while performing overdrive pacing of a reentrant tachycardia from a single pacing site at two different constant rates. The purpose of this article was to test the hypothesis that if an intracardiac recording site showing both orthodromic and antidromic capture with entrainment pacing is located suitably distant from the circuit, sudden shortening in conduction interval to that site may occur without any significant change in the bipolar electrogram morphology (i.e., atypical form of the fourth criterion). Atrial overdrive pacing of orthodromic tachycardia was performed in 20 patients with either left anterior (12 patients) or left posterior (8 patients) accessory pathways. We investigated the effects of overdrive pacing from the proximal or distal coronary sinus, specifically effects on the electrogram interval and the electrogram morphology at the right atrial appendage. Overdrive pacing of orthodromic tachycardia from the proximal coronary sinus was performed in 10 of the 12 patients with left anterior accessory pathways; those 10 patients demonstrated the first entrainment criterion at the right atrial appendage site. Overdrive pacing of orthodromic tachycardia at still shorter cycle lengths demonstrated a sudden shortening in conduction interval to the right atrial appendage site. Despite shortening in conduction interval the morphology of the right atrial appendage electrogram was completely or almost identical to that during orthodromic tachycardia, indicating an atypical form of the fourth criterion. This criterion was not demonstrated in patients with left posterior accessory pathways. Thus, atypical fourth entrainment criterion was demonstrated during overdrive pacing of orthodromic tachycardia from the proximal coronary sinus only in patients with left anterior accessory path ways. Demonstration of atypical fourth criterion seems largely dependent on the location of the accessory pathway, the pacing, and the recording sites.

Atypical antidromic resetting during programmed extrastimulation of reentrant ventricular tachycardia

A patient with reentrant ventricular tachycardia exhibited both the orthodromic and antidromic resetting responses at a single intracardiac recording site during programmed extrastimulation of ventricular tachycardia. The transition from orthodromic to antidromic resetting with extrastimulation demonstrated a sudden shortening in conduction interval to an electrogram recording site and unexpected identical morphology of the spontaneous and captured electrograms at that site, indicating atypical antidromic resetting. This newly observed resetting phenomenon with programmed extrastimulation suggests that the fourth entrainment criterion with overdrive pacing may likely be demonstrated in an atypical form; that is, a sudden shortening in conduction interval to an electrogram recording site may occur without any significant change in the bipolar electrogram morphology at that site when overdrive pacing is performed during tachycardia from a single pacing site at two different constant rates.