Entrainment of typical AV nodal reentrant tachycardia using para-Hisian pacing: evidence for a lower common pathway within the AV node

Para-Hisian Pacing: New Insights of an Old Pacing Maneuver

More than 2 decades ago, para-Hisian pacing was introduced to assess the pattern of retrograde conduction during electrophysiological studies. Although there is no ideal maneuver for every patient and condition, para-Hisian pacing is a valuable and handy strategy to differentiate between retrograde conduction over the atrioventricular node and the accessory pathways. The dynamic behavior of para-Hisian pacing, in a region with unique anatomical features, can produce various activation patterns and intriguing electrophysiological phenomena. Although the demonstration of a retrograde nodal activation pattern during para-Hisian pacing does not rule out the presence of an accessory pathway, evidence of retrograde conduction over an accessory pathway does not prove its active role in the culprit tachycardia. Multipolar His bundle recordings, detailed atrial mapping, and recognition of the truly captured structures and the impact of temporal changes of autonomic tone or pacing rates, are essential keys for accurate interpretation of this maneuver that may ultimately guide judicious catheter ablation of the arrhythmic substrate. This review aims to summarize the practical usefulness and potential pitfalls of the para-Hisian pacing maneuver, focusing on the interpretation of electrocardiograms and intracardiac recordings.

Superior-Type Fast-Slow Atrioventricular Nodal Reentrant Tachycardia Phenotype Mimicking the Slow-Fast Type

BACKGROUND

Superior-type fast-slow (sup-F/S-) atrioventricular nodal reentrant tachycardia (AVNRT) is a rare AVNRT variant using a superior slow pathway (SP) as the retrograde limb. Its intracardiac appearance, characterized by a short atrio-His (AH) interval and the earliest site of atrial activation in the His-bundle, is an initial indicator for making a diagnosis.

METHODS

Among 22 consecutive patients with sup-F/S-AVNRT, 3 (age, 68-81 years) patients had an apparent slow-fast (S/F-) AVNRT characterized by a long AH interval and the earliest site of atrial activation in or superior to the His-bundle region (tachy-long-AH).

RESULTS

The diagnosis of sup-F/S-AVNRT was based on the standard criteria in 2 patients and on the occurrence of Wenckebach-type atrioventricular block during tachycardia, which was attributable to a block at the lower common pathway (LCP) below the circuit of the AVNRT, detected owing to the lower common pathway potentials, in one patient. As with the typical S/F-AVNRT, tachy-long-AH was induced after a jump in the AH interval. In contrast to typical S/F-AVNRT, fluctuation in the ventriculoatrial interval was observed during the tachy-long-AH. Ventricular overdrive pacing was unable to entrain or terminate the tachy-long-AH. Moreover, the tachy-long-AH reciprocally transited to/from sup-F/S-AVNRT spontaneously or was triggered by ventricular contractions while the atrial cycle length and earliest site of atrial activation remained unchanged. Both tachycardias were cured by ablation at a single site in the right-side para-Hisian region of 2 patients and the noncoronary aortic cusp of one patient. Collectively, the essential circuit of both tachycardias was identical, and the tachy-long-AH was diagnosed as another phenotype of sup-F/S-AVNRT accompanied by sustained antegrade conduction via another bystander slow pathway breaking through the His-bundle owing to the repetitive antegrade block at the lower common pathway, thus representing a long AH interval during the ongoing sup-F/S-AVNRT.

CONCLUSIONS

An unknown sup-F/S-AVNRT phenotype exists that apparently mimics the typical S/F-AVNRT and is also an unknown subtype of apparent S/F-AVNRT.

Differentiating Atrioventricular Reentry Tachycardia and Atrioventricular Node Reentry Tachycardia Using Premature His Bundle Complexes

Background:

Current maneuvers for differentiation of atrioventricular node reentry tachycardia (AVNRT) and atrioventricular reentry tachycardia (AVRT) lack sensitivity and specificity for AVRT circuits located away from the site of pacing. We hypothesized that a premature His complex (PHC) will always perturb AVRT because the His bundle is obligatory to the circuit. Further, AVNRT could not be perturbed by a late PHC (≤20 ms ahead of the His) due to the retrograde His conduction time. Earlier PHCs can advance the AVNRT circuit but only by a quantity less than the prematurity of the PHC.

Methods:

High-output pacing at the distal His location delivered PHCs. AVRT was predicted when late PHCs perturbed tachycardia or when earlier PHCs led to atrial advancement by an amount equal or greater than the degree of PHC prematurity.

Results:

Among the 73 supraventricular tachycardias, the test accurately predicted AVRT (n=29) and AVNRT (n=44) in all cases. Late PHC advanced the circuit in all 29 AVRTs and none of the AVNRTs (sensitivity and specificity, 100%). With earlier PHCs, the degree of atrial advancement was equal or greater than the PHC prematurity in 26/29 AVRTs and none of the AVNRTs (90% sensitivity and 100% specificity). The mean prematurity of the PHC required to perturb AVNRT was 48 ms (range, 28–70 ms) and the advancement less than the prematurity of the PHC (mean, 32 ms; range, 18–54 ms).

Conclusions:

The responses to PHCs distinguished AVRT and AVNRT with 100% specificity and sensitivity.

Lower common pathway location detected by cryoablation of atrioventricular nodal reentrant tachycardia of the common variety

As different from radiofrequency current energy, cryofreezing energy is able to provide reversible effects on cardiac tissue, called "cryomapping," which enables us to predict the effects of a subsequent application of ablative energy. Cryomapping is able to delineate the anatomical location of the lower common pathway of atrioventricular nodal reentrant tachycardia.

Mark E Josephson: Clinical Investigator

Mark E Josephson entered the world of clinical cardiac electrophysiology (EP) almost at its inception (1972); with so much to learn and so many directions one could take, he dived into the field with unbridled enthusiasm and an uncommon - perhaps almost unique - aptitude for asking questions and finding ways to answer them. Few aspects of EP escaped his indelible influence. In this short paper, I will attempt to touch on some of the high points of his astounding career as a clinical investigator.

Classification, Electrophysiological Features and Therapy of Atrioventricular Nodal Reentrant Tachycardia

Atrioventricular nodal reentrant tachycardia (AVNRT) should be classified as typical or atypical. The term 'fast-slow AVNRT' is rather misleading. Retrograde atrial activation during tachycardia should not be relied upon as a diagnostic criterion. Both typical and atypical atrioventricular nodal reentrant tachycardia are compatible with varying retrograde atrial activation patterns. Attempts at establishing the presence of a 'lower common pathway' are probably of no practical significance. When the diagnosis of AVNRT is established, ablation should be only directed towards the anatomic position of the slow pathway. If right septal attempts are unsuccessful, the left septal side should be tried. Ablation targeting earliest atrial activation sites during typical atrioventricular nodal reentrant tachycardia or the fast pathway in general for any kind of typical or atypical atrioventricular nodal reentrant tachycardia, are not justified. In this review we discuss current concepts about the tachycardia circuit, electrophysiologic diagnosis, and ablation of this arrhythmia.

Principles of differential diagnostic pacing maneuvers: serial versus parallel conduction

In this article we will review differential diagnostic pacing maneuvers. It is not meant to be an exhaustive review of all such maneuvers. Rather, we offer some general analytic principles as they apply to electrophysiology (EP) and illustrate their use through several examples. Our hope is to provide a framework for thinking about electrogram data that acts more like a compass and map than like a specific set of directions. Amongst the most helpful pieces of advice that we can offer the EP trainee is to actively try to picture the waves of electricity spreading through the heart, passing beneath the recording electrodes and generating the electrograms you seek to interpret. Digest the fact that more than one propagation pattern can result in the same electrogram pattern and that differential diagnostic pacing is aimed at distinguishing between these possibilities. A fundamental tenet of differential diagnostic maneuvers of any kind (not simply pacing) is to choose a test that maximizes the difference between possible explanations. This perspective and a careful and meticulous cataloguing of what you can unambiguously conclude from the electrograms versus what remains to be determined via pacing offers the best approach to succeeding at EP. We will discuss pacing maneuvers in three contexts: differential diagnosis of narrow complex tachycardia, mapping of accessory pathways, and Para-Hisian pacing.

Participation of a concealed atriohisian tract in the reentrant circuit of the slow–fast type of atrioventricular nodal reentrant tachycardia

BACKGROUND

The retrograde fast pathway in typical atrioventricular nodal reentrant tachycardia (AVNRT) exhibits marked variation in its electrophysiologic properties.

OBJECTIVE

The purpose of this study was to characterize the retrograde fast pathway and localize the lower turnaround site of the reentrant circuit in typical AVNRT.

METHODS

Seventy-four patients with typical AVNRT were divided into two groups according to the response of the retrograde fast pathway to intravenous administration of adenosine triphosphate (ATP) during ventricular pacing: ATP-S [n = 47 (63.5%)] with and ATP-R without [n = 27 (36.5%)] His-atrial (H-A) block. H-A intervals were measured from the most proximal His-bundle electrogram to the earliest atrial activation during the tachycardia (HAt) and entrainment pacing from the parahisian right ventricular region (HAe). It was postulated that the HAt was the difference in conduction time between the lower common pathway (x) and retrograde fast pathway (y) (HAt = y - x), whereas HAe was the sum of the two (HAe = y + x). Hence, x = (HAe-HAt)/2. x >0 suggested the presence of a lower common pathway, whereas x <0 suggested the absence of a lower common pathway and lower turnaround site within the His bundle.

RESULTS

x was significantly smaller in ATP-R than ATP-S (-6 +/- 5 vs 4 +/- 4 ms, P <.05) and was <0 in 23 (85%) of 27 ATP-R patients. The maximal increment in H-A interval during ventricular pacing was significantly longer in ATP-S than ATP-R (35 +/- 33 vs 2 +/- 2 ms, P <.05).

CONCLUSION

A concealed atriohisian tract totally bypassing the atrioventricular node constituted the retrograde fast pathway in one third of all typical AVNRT cases.

Effects of right bundle branch block during atrioventricular nodal reentrant tachycardia

BACKGROUND

The significant role of bundle branch block during atrioventricular nodal reentrant tachycardia (AVNRT) is not clear. The purposes of this study were to study the effects of complete right bundle branch block (RBBB) on electrophysiological parameters during AVNRT and to define the significance of complete RBBB during AVNRT.

METHODS AND RESULTS

According to characteristics of electrocardiogram during sinus rhythm and AVNRT, 50 patients who underwent catheter ablation for slow-fast AVNRT were divided into three groups. Group I included 20 patients who had narrow QRS (< or = 110 ms) during sinus rhythm and AVNRT. Group II included 18 patients who had persistent RBBB (< or = 120 ms) during sinus rhythm and AVNRT. Group III included 12 patients who had narrow QRS during sinus rhythm, but they had narrow QRS and transient RBBB during AVNRT. The atrio-His (AH) interval (296+/-60 vs. 288+/-75 ms), His-ventricular (HV) interval (36+/-11 vs. 35+/-11 ms), His-atrial (HA) interval (72+/-24 vs. 71+/-28 ms), VA(HRA) interval (defined as the interval between the onset of ventricular depolarization and the onset of atrial activity of right high atrium; 34+/-24 vs. 37+/-25 ms), VA(CSO) interval (defined as the interval between the onset of ventricular depolarization and the onset of atrial activity of coronary sinus ostium; 13+/-28 vs. 26+/-23 ms) and tachycardia cycle length (TCL; 368+/-67 vs. 359+/-73 ms) during AVNRT were similar between group I and group II (all P > 0.05). In group III, the AH interval (255+/-81 vs. 246+/-83 ms), HV interval (44+/-5 vs. 42+/-11 ms), HA interval (66+/-19 vs. 70+/-15 ms), VA(HRA) interval (27+/-15 vs. 29+/-16 ms), VA(CSO) interval (23+/-25 vs. 21+/-25 ms) and TCL (322+/-76 vs. 316+/-77 ms) were not significantly different between AVNRT with narrow QRS and those with transient RBBB (all P > 0.05).

CONCLUSIONS

Persistent RBBB and transient RBBB have no significant effects on the electrophysiological parameters during AVNRT. These findings suggest that RBBB might not influence the conduction of lower common pathway or the circuit of AVNRT.

Significance of bundle branch block during atrioventricular nodal reentrant tachycardia

There are very limited data on the effects of bundle branch block (BBB) in patients with atrioventricular nodal reentrant tachycardia (AVNRT). Studies in a total of 155 patients with 162 episodes of AVNRT were retrospectively analyzed. A total of 38 patients (25%) developed spontaneous right BBB, whereas 5 (3%) developed left BBB during tachycardia. Five of the 38 (13%) with right BBB showed near identical prolongation of both the ventriculoatrial (VA) (15 +/- 5 ms; 10 to 23) and His to atrial intervals (HA) (14 +/- 4 ms; 10 to 20) with an identical atrial activation sequence for both right BBB or normal QRS tachycardia complexes. In contrast, all 5 patients with left BBB showed a decrease in the VA (-18 +/- 11 ms; 10 to 36) with unchanged HA comparing left BBB to normal QRS patterns during AVNRT. The magnitude of prolongation of the His to ventricular interval (HV) during left BBB (19 +/- 12 ms; 10 to 40) was nearly identical to the decrease in the VA. In conclusion, prolongation of VA and HA with unchanged HV in patients with AVNRT and right BBB suggests that right BBB is due to a block in the fibers in close proximity to the His recording site. The data suggest that fibers in the His bundle are predestined to activate the right bundle branch, and in AVNRT the lower turnaround point may be within the His bundle.

Location of the lower turnaround point in typical AV nodal reentrant tachycardia: a quantitative model

INTRODUCTION

Recent observations suggest that the circuit of AV nodal reentrant tachycardia (AVNRT) may extend down to the His bundle. The purpose of this study was to develop a quantitative model indicating the location of the lower turnaround point in AVNRT.

METHODS AND RESULTS

Slow pathway modification was performed in 70 patients with typical AVNRT. During sinus rhythm, ventricular pacing was performed with the AVNRT cycle length. During AVNRT, the HinitAinit interval was measured from initial His to the initial atrial deflection recorded in the His-bundle lead. During ventricular pacing, the HendAinit interval was measured from end of the His to the beginning of the atrial deflection. It was hypothesized that x reflects conduction time from the lower turnaround point to Ainit, whereas y reflects conduction time from the lower turnaround point to Hinit. Anterograde conduction during AVNRT and retrograde conduction during ventricular pacing were assumed to be identical if there was 1:1 retrograde conduction at the AVNRT cycle length. The following formulas describe the relation of the measured parameters: x - y = HinitAinit; and x + y = HendAinit. Resolving both formulas yields the unknown x and y: y = (HendAinit - HinitAinit)/2, x = (HendAinit + HinitAinit)/2. These criteria were present in 52 of 70 patients. The mean cycle length of AVNRT was 355 +/- 42 msec, mean HinitAinit was 54 +/- 27 msec, and mean HendAinit was 60 +/- 29 msec. Accordingly, in 20 of 52 patients, the lower turnaround point was located within the His bundle (y = -15.4 +/- 16.1 msec), in 3 of 52 it was in the nodal-His junctional area (y = 0), and in 29 of 52 it was above the His bundle (y = +12.7 +/- 10.3 msec). The HinitAinit interval was significantly longer (66 +/- 32 msec vs 47 +/- 20 msec; P = 0.02) and the HendAinit interval was significantly shorter (45 +/- 30 msec vs 69 +/- 24 msec; P = 0.004) when the first group was compared with the others.

CONCLUSION

In about 1 of 3 of patients with typical AVNRT, the lower turnaround point of the circuit is within the His bundle; in more than half of the patients it is above the His bundle. These data do not support the concept that all AVNRTs have an intranodal circuit, but are in accordance with the finding of longitudinal dissociation of the His bundle.