Sequence of retrograde atrial activation in patients with dual atrioventricular nodal pathways

An Unusual Cause of AV Dyssynchrony

A 71-year-old male with persistent atrial fibrillation and a dual chamber permanent pacemaker presented complaining of dyspnea on exertion, easy fatiguability, and intermittent cough. A 12-lead electrocardiogram revealed ventricular paced complexes, native QRS complexes, and irregular atrial activity. Herein we present an unusual mechanism of atrioventricular dyssynchrony. (Level of Difficulty: Intermediate.).

New insights into atrioventricular nodal anatomy, physiology, and immunochemistry: A comprehensive review and a proposed model of the slow-fast atrioventricular nodal reentrant tachycardia circuit in agreement with direct potential recordings in the Koch's triangle area

Atrioventricular nodal reentrant tachycardia (AVNRT) is the most frequent regular tachycardia in humans. In this review, we describe the most recent discoveries regarding the anatomical, physiological, and molecular biological features of the atrioventricular junction that could underlie the typical slow-fast AVNRT mechanisms, as these insights could lead to the proposal of a new theory concerning the circuit of this arrhythmia. Despite several models have been proposed over the years, the precise anatomical site of the reentrant circuit and the pathway involved in the slow-fast AVNRT have not been conclusively defined. One possible way to evaluate all the hypotheses regarding the nodal tachycardia circuit in humans is to map this circuit. Thus, we tried to identify the slow potential of nodal and inferior extension structures by using automated mapping of atrial activation during both sinus rhythm and typical slow-fast AVNRT. This constitutes a first step toward the definition of nodal area activation in sinus rhythm and during slow-fast AVNRT. Further studies and technical improvements in recording the potentials of the atrioventricular node structures are necessary to confirm our initial results.

Catheter ablation via the left atrium for atrioventricular nodal reentrant tachycardia: A narrative review

Background

Since 1996, it has been recognized that catheter ablation for atrioventricular nodal reentrant tachycardia (AVNRT) may require an approach through the left atrium.

Objective

The purposes are to present a case report and to provide a comprehensive narrative review on this topic.

Methods

A literature review of all articles that provided detailed information on patients who underwent catheter ablation via the left atrium for AVNRT was performed. The primary search queried PubMed using Medical Subject Headings (MeSH) terms "atrioventricular nodal reentrant tachycardia" and "left." The secondary search was performed by manual review of reference lists and Google Scholar citations of manuscripts retrieved by the primary search. The review was limited to the English language.

Results

The searches yielded 30 articles that described 79 patients. A case report was added. Therefore, the final review consisted of 80 patients. The prevalence of left atrial ablation for patients with AVNRT undergoing catheter ablation at tertiary care centers was approximately 1%. Failed right atrial ablation, with or without coronary sinus ablation, was the most common indication for left atrial ablation. Pooled data from 3 cohort studies estimated the acute success rate for radiofrequency ablation of the slow pathway at the septal or inferoparaseptal segments of the mitral valve annulus after failed right-sided ablation to be 90%. There were no reports of atrioventricular block requiring permanent pacemaker implantation.

Conclusion

Catheter ablation of the slow pathway via the left atrium is an important technique for AVNRT cases that are refractory to conventional ablation.

Reflections on the early invasive clinical cardiac electrophysiology era through fifty manuscripts: 1967-1992

In 1967, researchers in The Netherlands and France independently reported a new technique, later called programmed electrical stimulation. The ability to reproducibly initiate and terminate arrhythmias heralded the beginning of invasive clinical cardiac electrophysiology as a medical discipline. Over the next fifty years, insights into the pathophysiologic basis of arrhythmias would transform the field into an interventional specialty with a tremendous armamentarium of procedures. In 2015, the variety and complexity of these procedures were major reasons that led to the recommendation for an increase in the training period from one year to two years. The purpose of this manuscript is to present fifty manuscripts from the early invasive clinical cardiac electrophysiology era, between 1967 and 1992, to serve as an educational resource for current and future electrophysiologists. It is our hope that reflection on the transition from a predominantly noninvasive discipline to one where procedures are commonly utilized will lead to more thoughtful patient care today and to inspiration for innovation tomorrow. In the words of the late Dr. Mark E. Josephson, "It is only by getting back to the basics that the field of electrophysiology will continue to grow instead of stagnate."

A new criterion to differentiate atrioventricular nodal reentrant tachycardia from atrioventricular reciprocating tachycardia: Combined AVR criterion

AIM

A combined aVR criterion is described as the presence of a pseudo r' wave in aVR during tachycardia in patients without r' wave in aVR in sinus rhythm and/or a ≥50% increase in r' wave amplitude compared to sinus rhythm in patients with r' wave in the basal aVR lead. We aimed to investigate the use of combined aVR criterion in differential diagnosis of atrioventricular nodal reentrant tachycardia (AVNRT) and atrioventricular reciprocating tachycardia (AVRT).

METHODS

In this prospective study, 480 patients with inducible narrow QRS supraventricular tachycardia (SVT) were included. Twelve-lead electrocardiogram (ECG) was conducted during tachycardia and sinus rhythm. The patients were divided into two groups according to the arrhythmia mechanism that determined via EPS, AVNRT, and AVRT. Criteria of narrow QRS complex tachycardia were compared between the two groups.

RESULTS

AVNRT was present in 370 (77%) patients and AVRT in 110 (23%) patients. Combined aVR criterion was found to be more frequent in patients with AVNRT (84.1% and 9.1%, p < 0.001). In logistic regression analysis, combined aVR criterion and classical ECG criterion were found to be the most important predictors of AVNRT (p < 0.001). The sensitivity, specificity, positive predictive value, and negative predictive value of the combined aVR criterion for AVNRT were 84.1%, 90.9%, 96.9%, and 62.9%, respectively.

CONCLUSION

In the differential diagnosis of patients with SVT, the combined aVR criterion identifies the presence of AVNRT with an independent and acceptable diagnostic value. In addition to classical ECG criteria for AVNRT, it is necessary to evaluate the combined aVR criterion in daily practice.

Catheter ablation for supraventricular tachycardias: contemporary issues

The treatment of cardiac arrhythmias has evolved significantly over the last 30 years. Understanding of arrhythmia mechanisms has led to pharmacologic therapies, surgical interventions and the widely used percutaneous catheter ablation techniques. The focus of this review is centered on the current catheter ablation therapies available for supraventricular tachycardia. We will discuss current management strategies including challenges when considering catheter ablation therapy for management of supraventricular tachycardias: atrioventricular nodal reentrant tachycardia, atrioventricular reentrant tachycardia utilizing an accessory pathway, atrial tachycardia and atrial flutter. Selected contemporary issues related to supraventricular tachycardia physiology, ablation approaches and ablation outcomes and complications will be discussed. Future goals for electrophysiologists are to continue to improve procedural safety and efficiency, while maintaining the impressive success rates that have been achieved.

Slow pathway ablation for typical atrioventricular nodal re-entrant tachycardia significantly alters the autonomic modulation of atrioventricular conduction

PURPOSE

Atrioventricular (AV) conduction turbulence, biphasic dromotropic response of AV node to single ventricular premature contraction (VPC), consists of early shortening and later prolongation of AV conduction intervals due to the direct electrophysiological mechanisms and perturbation in autonomic modulation. We investigated the acute effect of radiofrequency catheter ablation of slow pathway on AV turbulence.

METHODS

The electrophysiological study was performed in 18 patients (7 men, mean age 49 ± 15 years) undergoing catheter ablation for AV nodal reentrant tachycardia. The stimulation protocol consisting of series of isolated VPC (coupling interval of 273 ± 23 ms) delivered from right ventricle apex during constant atrial pacing at 100 bpm was performed immediately prior to and 8 ± 4 min after successful slow-pathway ablation. Averaged post-VPCs profiles of AV conduction intervals were analyzed by purpose-written software. The descriptors of AV turbulence, turbulence onset (TOAV), turbulence slope (TSAV), and AV recovery (R AV) were assessed.

RESULTS

Slow-pathway ablation suppressed the AV nodal responsiveness to VPC as evidenced by significant reduction of AV turbulence indices: TOAV: -6.4 ± 7.5 % vs. -4.3 ± 6.1 % (p < 0.05); TSAV: 2.0 ± 2.6 ms/RRi vs. 1.0 ± 0.7 ms/RRi (p < 0.05); and R AV: -13.8 ± 7.3 % vs. -6.5 ± 12.7 % (p < 0.05).

CONCLUSIONS

Slow-pathway ablation significantly attenuated both vagal and non-autonomic modulation of AV nodal conduction. This effect is likely due to direct thermal injury of AV node associated with the change of properties of AV nodal fast-pathway although specific alteration of peri-AV nodal ganglionated plexi or their neural inputs into the AV node cannot be excluded.

A novel manoeuvre for discerning supraventricular tachycardia mechanism

AIMS

Discerning supraventricular tachycardia (SVT) mechanism during catheter ablation procedures can be difficult and time-consuming, which, when combined with diagnostic error, places patients at risk of unnecessary complications. Distinguishing atrial tachycardia (AT) from AV nodal re-entry tachycardia (AVNRT) may be particularly vexatious. Value-added techniques are thus always welcome, particularly if they are not time-consuming nor require complex intracardiac lead configurations. In this study, we assessed whether a new technique, simultaneous right atrial and right ventricular pacing (RA + RV) during ongoing SVT, met these criteria.

METHODS AND RESULTS

Using a simple intracardiac lead configuration (right atrial appendage, His bundle, right ventricular apex), the response to RA + RV delivered at 80-90% of the SVT cycle length, was examined in 80 patients referred for catheter ablation. In each patient, the actual tachycardia mechanism was adjudicated by standard electrophysiologic criteria ± successful catheter ablation. Mechanisms of SVT included, non-exclusively, AVNRT (24 patients), accessory pathway-mediated (orthodromic) re-entry (AVRT; 23 patients), AT (10 patients), and sinus tachycardia (ST induced with isoproterenol; 49 patients). Immediately after cessation of RA + RV pacing during persistent SVT, the first intracardiac electrogram observed was right atrial in all AT whereas it was His bundle in all AVNRT. The response during AVRT was mixed.

CONCLUSIONS

In this preliminary evaluation, RA + RV pacing appears to add value to the existing armamentarium of electrophysiologic indices to discern SVT mechanism, in particular with respect to discriminating between AVNRT and AT.

Utility of Atrial and Ventricular Cycle Length Variability in Determining the Mechanism of Paroxysmal Supraventricular Tachycardia

INTRODUCTION

No prior studies have systematically investigated the diagnostic value of cycle length (CL) variability in differentiating the mechanism of paroxysmal supraventricular tachycardia (PSVT).

METHODS AND RESULTS

We studied 173 consecutive patients with PSVT; 86 typical atrioventricular nodal reentrant tachycardia (AVNRT), 11 atypical AVNRT, 47 orthodromic reciprocating tachycardia (ORT), and 29 with atrial tachycardia (AT). Two consecutive atrial cycles that displayed the most CL variability were selected for analysis. One hundred and twenty-six patients (73%) had > or = 15 msec variability in tachycardia CL. The change in atrial CL predicted the change in subsequent ventricular CL in six of eight patients (75%) with atypical AVNRT, 18 of 21 patients (86%) with AT, in none of 66 patients with typical AVNRT, and in 32 patients with ORT. The change in atrial CL was predicted by the change in preceding ventricular CL in 55 of 66 patients (83%) with typical AVNRT, no patient with atypical AVNRT, 27 of 31 patients (87%) with ORT, and one of 21 patients (5%) with AT. The sensitivity, specificity, and positive and negative predictive values of a change in atrial CL predicting the change in ventricular CL for AT or atypical AVNRT were 83%, 100%, 100%, and 95%, respectively. The corresponding values for the change in atrial CL being predicted by the change in the preceding ventricular CL for typical AVNRT or ORT were 85%, 97%, 99%, and 65%, respectively.

CONCLUSION

Tachycardia CL variability > or = 15 msec is common in PSVT. A change in atrial CL that predicts the change in subsequent ventricular CL strongly favors AT or atypical AVNRT. A change in atrial CL that is predicted by the change in the preceding ventricular CL favors typical AVNRT or ORT.

Electrophysiologic delineation of the tachycardia circuit in the slow-slow form of atrioventricular nodal reentrant tachycardia

BACKGROUND

Little is known about the exact boundaries of the reentrant circuit in the slow-slow form of atrioventricular nodal reentrant tachycardia (AVNRT).

OBJECTIVE

The purpose of this study was to examine the tachycardia circuit in the slow-slow form of AVNRT.

METHODS

Single extrastimuli were delivered during the slow-slow form of AVNRT at 10 sites along the right interatrial septum: superior portion of the His-bundle (HB) site, the HB site, three equidistantly divided sites of the AV junction between HB site and coronary sinus ostium (CSOS; sites S, M, and I), and inferior, superior, posterior, posteroinferior, and internal portions of the CSOS in 13 patients. The longest coupling interval of a single extrastimulus that reset the tachycardia and the following return cycle were measured.

RESULTS

The tachycardia cycle length was 409 +/- 50 ms. The earliest atrial electrogram during tachycardia was observed at site I in all patients. The longest coupling intervals at superior-HB, HB site, sites S, M, and I, and inferior-CSOS, superior-CSOS, posterior-CSOS, posteroinferior-CSOS, and internal-CSOS were 340 +/- 52, 355 +/- 50, 367 +/- 50, 378 +/- 51, 398 +/- 49, 398 +/- 52, 355 +/- 60, 351 +/- 50, 371 +/- 48, and 363 +/- 54 ms, respectively. The following return cycles were 468 +/- 52, 453 +/- 52, 442 +/- 52, 431 +/- 50, 411 +/- 52, 410 +/- 49, 454 +/- 45, 457 +/- 57, 438 +/- 54, and 445 +/- 53 ms, respectively. The longest coupling intervals at site I and inferior-CSOS were significantly longer than those at the other sites (P <.0001). The return cycles at site I and inferior-CSOS did not differ from the tachycardia cycle length, whereas those at the other sites were significantly longer than the tachycardia cycle length (P <.0001).

CONCLUSION

Site I and inferior-CSOS are involved in the slow-slow form of AVNRT circuit, and the atrial tissue between those sites form an integral limb of the reentrant circuit.

Paroxysmal Supraventricular Tachycardia: A Century of Progress

This article reviews progress in the understanding of AV junctional reentrant tachycardia and accessory pathway-mediated tachycardia in the twentieth century and in the early part of the twenty-first century. Emphasis is placed on the contributions of John Uther and the department he founded at Westmead Hospital.

Retrograde slow pathway conduction in patients with atrioventricular nodal re-entrant tachycardia

AIMS

To study retrograde slow pathway conduction by means of right- and left-sided septal mapping.

METHODS AND RESULTS

Nineteen patients with slow-fast atrioventricular nodal re-entrant tachycardia (AVNRT) were studied before and after slow pathway ablation. Simultaneous His bundle recordings from right and left sides of the septum, using trans-aortic and trans-septal electrodes, were made during right ventricular pacing. Pre-ablation, decremental retrograde ventriculo-atrial (VA) conduction without jumps or discontinuities was recorded in eight patients (group 1). In six patients, retrograde conduction jumps were demonstrated (group 2) and in the remaining four patients, there was minimal prolongation of stimulus to atrium (St-A) intervals (group 3). The maximal difference (Delta St-A) between St-A intervals obtained with pacing at a constant cycle length of 500 ms and at the cycle length with maximal retrograde VA prolongation was significantly longer measured from the right His compared with the left His (122 +/- 25 vs. 110 +/- 33 ms, P = 0.02, respectively) in group 1 and group 2 (140 +/- 23 vs. 110 +/- 35 ms, P = 0.03), but not in group 3 (10 +/- 4 vs. 13 +/- 8 ms, P = 0.35). Post-ablation, Delta St-A intervals were similar between right and left His recordings (77 +/- 37 vs. 76 +/- 33 ms, P = 0.53, respectively) in group 1, (100 +/- 24 vs. 103 +/- 21 ms, P = 0.35) group 2, and (63 +/- 32 vs. 66 +/- 33 ms, P = 0.35) group 3.

CONCLUSION

In patients with typical AVNRT, retrograde conduction through the slow pathway results in earliest retrograde atrial activation on the left side of the septum and catheter ablation in the right inferoparaseptal area abolishes this pattern. These findings are compatible with the concept of slow pathway conduction by means of the inferior AV nodal extensions.

The Electrophysiological Characteristics in Patients with Ventricular Stimulation Inducible Fast-Slow Form Atrioventricular Nodal Reentrant Tachycardia

BACKGROUND

Atrioventricular nodal reentrant tachycardia (AVNRT) can usually be induced by atrial stimulation. However, it seldom may be induced with only ventricular stimulation, especially the fast-slow form of AVNRT. The purpose of this retrospective study was to investigate the specific electrophysiological characteristics in patients with the fast-slow form of AVNRT that could be induced with only ventricular stimulation.

METHODS

The total population consisted of 1,497 patients associated with AVNRT, and 106 (8.4%) of them had the fast-slow form of AVNRT and 1,373 (91.7%) the slow-fast form of AVNRT. In patients with the fast-slow form of AVNRT, the AVNRT could be induced with only ventricular stimulation in 16 patients, Group 1; with only atrial stimulation or both atrial and ventricular stimulation in 90 patients, Group 2; and with only atrial stimulation in 13 patients, Group 3. We also divided these patients with slow-fast form AVNRT (n = 1,373) into two groups: those that could be induced only by ventricular stimulation (Group 4; n = 45, 3%) and those that could be induced by atrial stimulation only or by both atrial and ventricular stimulation (n = 1.328, 97%).

RESULTS

Patients with the fast-slow form of AVNRT that could be induced with only ventricular stimulation had a lower incidence of an antegrade dual AVN physiology (0% vs 71.1% and 92%, P < 0.001), a lower incidence of multiple form AVNRT (31% vs 69% and 85%, P = 0.009), and a more significant retrograde functional refractory period (FRP) difference (99 +/- 102 vs 30 +/- 57 ms, P < 0.001) than those that could be induced with only atrial stimulation or both atrial and ventricular stimulation. The occurrence of tachycardia stimulated with only ventricular stimulation was more frequently demonstrated in patients with the fast-slow form of AVNRT than in those with the slow-fast form of AVNRT (15% vs 3%, P < 0.001). Patients with the fast-slow form of AVNRT that could be induced with only ventricular stimulation had a higher incidence of retrograde dual AVN physiology (75% vs 4%, P < 0.001), a longer pacing cycle length of retrograde 1:1 fast and slow pathway conduction (475 +/- 63 ms vs 366 +/- 64 ms, P < 0.001; 449 +/- 138 ms vs 370 +/- 85 ms, P = 0.009), a longer retrograde effective refractory period of the fast pathway (360 +/- 124 ms vs 285 +/- 62 ms, P = 0.003), and a longer retrograde FRP of the fast and slow pathway (428 +/- 85 ms vs 362 +/- 47 ms, P < 0.001 and 522 +/- 106 vs 456 +/- 97 ms, P = 0.026) than those with the slow-fast form of AVNRT that could be induced with only ventricular stimulation.

CONCLUSION

This study demonstrated that patients with the fast-slow form of AVNRT that could be induced with only ventricular stimulation had a different incidence of the antegrade and retrograde dual AVN physiology and the specific electrophysiological characteristics. The mechanism of the AVNRT stimulated only with ventricular stimulation was supposed to be different in patients with the slow-fast and fast-slow forms of AVNRT.

Atrial activation during atrioventricular nodal reentrant tachycardia: Studies on retrograde fast pathway conduction

BACKGROUND

Detailed right and left septal mapping of retrograde atrial activation during typical atrioventricular nodal reentrant tachycardia (AVNRT) has not been undertaken and may provide insight into the complex physiology of AVNRT, especially the anatomic localization of the fast and slow pathways.

OBJECTIVES

The purpose of this study was to investigate the pattern of retrograde atrial activation during typical AVNRT by means of right-sided and left-sided septal mapping and implementation of pacing maneuvers for separating atrial and ventricular electrograms recorded during tachycardia.

METHODS

Twenty-two patients with slow-fast AVNRT were studied by means of simultaneous His-bundle recordings from the right and left sides of the septum. Patterns of retrograde atrial activation were recorded during tachycardia following specific pacing maneuvers and during right ventricular apical (RVA) pacing at the tachycardia cycle length.

RESULTS

The pattern of retrograde atrial activation could be mapped in 17 of 22 patients during AVNRT. In 9 (53%) patients, the earliest retrograde atrial activation was recorded on the left side of the septum, in 3 (17%) patients on the right side, and in 5 (29%) patients both right and left atrial septal electrograms occurred simultaneously. Stimulus to atrial electrogram times recorded during RVA pacing in 14 patients were 138.5 ms from the right His bundle, 134.5 ms from the left His bundle, and 148.0 ms from the ostium of the coronary sinus (P <.001). The predominant site of earliest retrograde atrial activation during RVA pacing was the left side of the septum (10 patients [71%]). Only 8 (57%) of 14 patients demonstrated concordance in the pattern of retrograde atrial activation during AVNRT and RVA pacing.

CONCLUSION

Earliest retrograde atrial activation during AVNRT is most often recorded on the left side of the septum. Breakthrough of atrial activation may be discordant from that observed during RVA pacing.

Unique electrophysiologic characteristics of atrioventricular nodal reentrant tachycardia with different ventriculoatrial block patterns: effects of slow pathway ablation and insights into the location of the reentrant circuit

BACKGROUND

The electrophysiologic mechanisms of different ventriculoatrial (VA) block patterns during atrioventricular nodal reentrant tachycardia (AVNRT) are poorly understood.

OBJECTIVES

The purpose of this study was to characterize AVNRTs with different VA block patterns and to assess the effects of slow pathway ablation.

METHODS

Electrophysiologic data from six AVNRT patients with different VA block patterns were reviewed.

RESULTS

All AVNRTs were induced after a sudden AH "jump-up" with the earliest retrograde atrial activation at the right superoparaseptum. Different VA block patterns comprised Wenckebach His-atrial (HA) block (n = 4), 2:1 HA block (n = 1), and variable HA conduction times during fixed AVNRT cycle length (CL) (n = 1). Wenckebach HA block during AVNRT was preceded by gradual HA interval prolongation with fixed His-His (HH) interval and unchanged atrial activation sequence. AVNRT with 2:1 HA block was induced after slow pathway ablation for slow-slow AVNRT with 1:1 HA conduction, and earliest atrial activation shifted from right inferoparaseptum to superoparaseptum without change in AVNRT CL. The presence of a lower common pathway was suggested by a longer HA interval during ventricular pacing at AVNRT CL than during AVNRT (n = 5) or Wenckebach HA block during ventricular pacing at AVNRT CL (n = 1). In four patients, HA interval during ventricular pacing at AVNRT CL was unusually long (188 +/- 30 ms). Ablations at the right inferoparaseptum rendered AVNRT noninducible in 5 (83%) of 6 patients.

CONCLUSION

Most AVNRTs with different VA block patterns were amenable to classic slow pathway ablation. The reentrant circuit could be contained within a functionally protected region around the AV node and posterior nodal extensions, and different VA block patterns resulted from variable conduction at tissues extrinsic to the reentrant circuit.

The history of AV nodal reentry

Though patients with AV nodal reentry are now routinely cured by catheter ablation, the basic mechanism of this disorder is still under debate. The putative mechanism of AV node reentry was first discovered by the elegant work of Gordon Moe. He demonstrated the existence of dual pathways and echo beats in rabbits. Building on these seminal observations, the mechanism of AVNRT has burgeoned to include the possibility of left atrial input into the node. The first curative nonpharmacologic procedures involved surgical dissection around the AV node and the procedure was rapidly supplanted by catheter ablation procedures. The initial ablative procedure targeted the fast pathway, but later observations showed that ablation of the slow pathway was more effective and safer. Cure of AV nodal reentry which is the most common cause of paroxysmal supraventricular tachycardia became possible through the cooperative efforts of anatomists, physiologists, surgeons, and clinical electrophysiologists.

The Electrophysiologic Characteristics in Patients with Only Ventricular-Pacing Inducible Slow–Fast Form Atrioventricular Nodal Reentrant Tachycardia

BACKGROUND

Atrioventricular nodal reentrant tachycardia (AVNRT) can be usually induced by atrial pacing or extrastimulation. However, it is less commonly induced only by ventricular pacing or extrastimulation.

OBJECTIVE

The purpose of this retrospective study was to investigate the electrophysiologic characteristics in patients with slow-fast form AVNRT that could be induced only by ventricular pacing or extrastimulation.

METHODS

The total population was 1497 patients associated with AVNRT. There were 1373 (91.7%) patients who had slow-fast form AVNRT included in our study. Group 1 (n = 45) could be induced only by ventricular pacing or extrastimulation, and Group 2 (n = 1328) could be induced by only atrial stimulation or both atrial and ventricular stimulation. The electrophysiologic characteristics of the group 1 and group 2 patients were compared.

RESULTS

Group 1 patients had a significantly lower incidence of both antegrade and retrograde dual AV nodal pathways. The pacing cycle length (CL) of the antegrade 1:1 fast pathway (FP) and antegrade ERP of the FP were both significantly shorter in Group 1 patients. Mean antegrade FRP of the fast and slow pathways were significantly shorter in Group 1 patients. The differences of pacing CL of 1:1 antegrade conduction, antegrade ERP and FRP were much longer in Group 2 patients.

CONCLUSION

This study demonstrated the patients with slow-fast form AVNRT that could be induced only by ventricular stimulation had a lower incidence of dual AV nodal pathways and the different electrophysiologic characteristics (shorter pacing CL of the antegrade 1:1 FP, antegrade ERP of the FP and the differences of pacing CL of 1:1 antegrade conduction, antegrade ERP and FRP) from the other patients. The specific electrophysiologic characteristics in such patients could be the reason that could be induced only by ventricular stimulation.

History of arrhythmias

A historical overview is given on the techniques to record the electrical activity of the heart, some anatomical aspects relevant for the understanding of arrhythmias, general mechanisms of arrhythmias, mechanisms of some specific arrhythmias and nonpharmacological forms of therapy. The unravelling of arrhythmia mechanisms depends, of course, on the ability to record the electrical activity of the heart. It is therefore no surprise that following the construction of the string galvanometer by Einthoven in 1901, which allowed high-fidelity recording of the body surface electrocardiogram, the study of arrhythmias developed in an explosive way. Still, papers from McWilliam (1887), Garrey (1914) and Mines (1913, 1914) in which neither mechanical nor electrical activity was recorded provided crucial insights into re-entry as a mechanism for atrial and ventricular fibrillation, atrioventricular nodal re-entry and atrioventricular re-entrant tachycardia in hearts with an accessory atrioventricular connection. The components of the electrocardiogram, and of extracellular electrograms directly recorded from the heart, could only be well understood by comparing such registrations with recordings of transmembrane potentials. The first intracellular potentials were recorded with microelectrodes in 1949 by Coraboeuf and Weidmann. It is remarkable that the interpretation of extracellular electrograms was still controversial in the 1950s, and it was not until 1962 that Dower showed that the transmembrane action potential upstroke coincided with the steep negative deflection in the electrogram. For many decades, mapping of the spread of activation during an arrhythmia was performed with a "roving" electrode that was subsequently placed on different sites on the cardiac surface with a simultaneous recording of another signal as time reference. This method could only provide reliable information if the arrhythmia was strictly regular. When multiplexing systems became available in the late 1970s, and optical mapping in the 1980s, simultaneous registrations could be made from many sites. The analysis of atrial and ventricular fibrillation then became much more precise. The old question whether an arrhythmia is due to a focal or a re-entrant mechanism could be answered, and for atrial fibrillation, for instance, the answer is that both mechanisms may be operative. The road from understanding the mechanism of an arrhythmia to its successful therapy has been long: the studies of Mines in 1913 and 1914, microelectrode studies in animal preparations in the 1960s and 1970s, experimental and clinical demonstrations of initiation and termination of tachycardias by premature stimuli in the 1960s and 1970s, successful surgery in the 1980s, the development of external and implantable defibrillators in the 1960s and 1980s, and finally catheter ablation at the end of the previous century, with success rates that approach 99% for supraventricular tachycardias.

"V-H-A Pattern" as a Criterion for the Differential Diagnosis of Atypical AV Nodal Reentrant Tachycardia from AV Reciprocating Tachycardia

BACKGROUND

During ventricular extrastimulation, His bundle potential (H) following ventricular (V) and followed by atrial potentials (A), i.e., V-H-A, is observed in the His bundle electrogram when ventriculo-atrial (VA) conduction occurs via the normal conduction system. We examined the diagnostic value of V-H-A for atypical form of atrioventricular nodal reentrant tachycardia (AVNRT), which showed the earliest atrial activation site at the posterior paraseptal region during the tachycardia.

METHODS

We prospectively examined the response of VA conduction to ventricular extrastimulation during basic drive pacing performed during sinus rhythm in 16 patients with atypical AVNRT masquerading atrioventricular reciprocating tachycardia (AVRT) utilizing a posterior paraseptal accessory pathway and 21 with AVRT utilizing a posterior paraseptal accessory pathway. Long RP' tachycardia with RP'/RR > 0.5 was excluded. The incidences of V-H-A and dual AV nodal physiology (DP) were compared between atypical AVNRT and AVRT.

RESULTS

V-H-A was demonstrated in all the 16 patients (100%) in atypical AVNRT and in only 1 of the 21 (5%) in AVRT (P < 0.001). DP was demonstrated in 10 patients (63%) in atypical AVNRT and in 4 (19%) in AVRT (P < 0.05). The sensitivity of V-H-A for atypical AVNRT was higher than that of DP (P < 0.05). Positive and negative predictive values were 94% and 100%, respectively, for V-H-A and 71% and 74%, respectively, for DP.

CONCLUSIONS

The appearance of V-H-A during ventricular extrastimulation is a simple criterion for differentiating atypical AVNRT masquerading AVRT from AVRT utilizing a posterior paraseptal accessory pathway.

Relation Between the AH Interval and the Ablation Site in Patients with Atrioventricular Nodal Reentrant Tachycardia

The determinants of slow pathway conduction in patients with AV nodal reentrant tachycardia (AVNRT) are still unknown, and great differences in the AH interval during slow pathway conduction are observed between patients. In 35 patients with typical AVNRT who underwent successful slow pathway ablation (defined as complete elimination of dual pathway physiology), the A2H2 interval at the "jump" during programmed atrial stimulation and the AH interval during AVNRT (as a reflection of slow pathway conduction time) and the fluoroscopic distance between the successful ablation site and the His-bundle recording site and between the coronary sinus ostium (CSO) and the His-bundle recording site were determined. The mean (+/- SEM) AH interval during slow pathway conduction was 323 +/- 12 ms with programmed stimulation and 310 +/- 10 ms during AVNRT. The mean number of energy applications was 8 +/- 1 (range 1-21). The mean distances between (1) the successful ablation site and the His bundle recording site and (2) between the CSO and the His-bundle recording site were 24 +/- 1 and 28 +/- 1 mm in the RAO and 23 +/- 1 and 28 +/- 1 mm in the LAO projections, respectively. The AH interval during slow pathway conduction correlated significantly with the distance between the successful ablation site and the His-bundle (P < 0.001) but not with the distance between CSO and His-bundle recording site. There is a significant correlation between the AH interval during slow pathway conduction and the distance of the successful ablation site from the His bundle. This relationship (1) suggests that, in addition to functional factors, anatomic factors influence slow pathway conduction and (2) may be helpful in determining the initial energy application site during slow pathway ablation.

Retrograde cycle length alternans during supraventricular tachycardia: an unusual tachycardia mechanism

Cycle length alternans is occasionally seen during supraventricular tachycardia due to oscillations in the antegrade atrioventricular nodal (AVN) refractoriness. However, alternans due to retrograde variation in AVN conduction has not been reported. This report describes the case of a 36-year-old man with atypical AVN reentry tachycardia (AVNRT) whose episodes of tachycardia were characterized by continuous oscillations in retrograde AVN conduction. Ablation at one spot eliminated the tachycardia. Cycle length alternans due to oscillations in retrograde AVN conduction, although rare, can be seen during atypical AVNRT and should be considered.

Radiofrequency ablation of atrial flutter: a randomized controlled study of two anatomic approaches

Atrial flutter often results from a macroreentrant circuit that uses anatomic structures within the right atrium as its borders. RF ablation at the site of an obligatory isthmus can eliminate the atrial flutter circuit. The aim of this study was to compare two approaches to atrial flutter ablation: the septal (septal aspect of the tricuspid valve annulus to coronary sinus ostium and Eustachian ridge) approach versus the posterior (inferior vena cava to tricuspid valve annulus) approach. Twenty patients were randomized to either the "septal" or "posterior" approach. Entrainment mapping and/or confirmation of bidirectional isthmus conduction at baseline were performed in those patients in atrial flutter and normal sinus rhythm, respectively. RF ablation was performed with standard catheters and techniques. Crossover was permitted after two lines of RF lesions. Endpoints included acute success rates and fluoroscopy times. There was no statistically significant difference in the success rate between the two approaches using intention-to-treat analysis. Fluoroscopy times in the septal versus posterior approaches were 58.4 +/- 30.3 versus 70.8 +/- 31.1 minutes, respectively (P = 0.7). There was more frequent crossover in patients assigned to the septal approach and the one major complication, atrioventricular block, also occurred using this approach. There was no statistically significant difference in the success rate or fluoroscopy times between the septal and posterior approaches to atrial flutter ablation. However, given the risk of atrioventricular block with the septal approach, the posterior approach should be the preferred initial choice.

Standard Right Atrial Ablation is Effective for Atrioventricular Nodal Reentry with Earliest Activation in the Coronary Sinus

INTRODUCTION

Reports suggest that coronary sinus (CS) or left atrial ablations may be necessary for treatment of AV nodal reentrant tachycardia (AVNRT) with earliest retrograde atrial activation in the CS. We assessed the efficacy of standard right atrial catheter ablation approaches in these tachycardias and determined the incidence of earliest activation in the CS in AVNRT.

METHODS AND RESULTS

We retrospectively evaluated intracardiac recordings from 225 consecutive patients who underwent electrophysiologic studies and radiofrequency (RF) ablation for AVNRT in two institutions. Atrial activation during AVNRT was evaluated using multiple catheters according to standard protocol used in our laboratories. RF ablations in the triangle of Koch were performed in all patients. Eighteen of 225 patients (8%) had earliest activation in one of the CS poles. The demographics and AVNRT characteristics of these 18 patients were similar to those of the other 207 patients who did not have CS as earliest activation site and included both typical and atypical AVNRT. Following RF ablation, none of the 18 patients had inducible AVNRT.

CONCLUSION

Successful RF ablation can be performed at standard sites in the triangle of Koch regardless of earliest site of atrial activation. The incidence of CS as earliest retrograde atrial activation site in AVNRT is 8%.

Usefulness of ST-segment elevation in lead aVR during tachycardia for determining the mechanism of narrow QRS complex tachycardia

In the present study, we analyzed ST-segment elevation in lead aVR during tachycardia to differentiate the narrow QRS complex tachycardia. A total of 338 12-lead electrocardiograms during narrow QRS complex tachycardia were analyzed. Each patient underwent a complete electrophysiologic study. There were 161 episodes of atrioventricular nodal reentrant tachycardia (AVNRT), 165 episodes of atrioventricular reciprocating tachycardia (AVRT), and 12 episodes of atrial tachycardia (AT). The prevalence of aVR ST-segment elevation was 71% for AVRT, 31% for AVNRT, and 16% for AT. For ST-T changes in different leads, logistic regression analysis showed aVR ST-segment elevation was the only significant factor to differentiate the types of narrow QRS complex tachycardia (p<0.001 for AVRT and AVNRT; p=0.02 for AVRT and AT). The sensitivity, specificity, and accuracy of aVR ST-segment elevation to differentiate AVRT from AVNRT and AT were 71%, 70%, and 70%, respectively. Among 117 episodes of AVRT with aVR ST-segment elevation, there were 76 (65%) left side, 23 (20%) right side, 14 (12%) posterior septal, and 4 (3%) antero- and mid-septal accessory pathways (p=0.002). In conclusion, aVR ST-segment elevation during narrow QRS complex tachycardia favors the atrioventricular reentry through an accessory pathway as the mechanism of the tachycardia.

Role of Compact Node and Posterior Extension in Direction-Dependent Changes in Atrioventricular Nodal Function in Rabbit

INTRODUCTION

AV nodal conduction properties differ in the anterograde versus the retrograde direction. The underlying substrate remains unclear. We propose that direction-dependent changes in AV nodal function are the net result of those occurring in the slow and fast pathways.

METHODS AND RESULTS

Anterograde and retrograde AV nodal properties were determined with a premature protocol before and after posterior extension (slow pathway) ablation, and before and after upper compact node (fast pathway) ablation. Each ablation was performed in a different group of six rabbit heart preparations. In control, nodal minimum conduction time (NCTmin) and effective refractory period (ERPN) typically were longer, and maximum conduction time (NCTmax) was shorter in the retrograde compared to the anterograde direction. Posterior extension ablation prolonged anterograde ERPN from 91 +/- 10 ms to 141 +/- 15 ms (P < 0.01) and shortened NCTmax from 150 +/- 13 ms to 82 +/- 7 ms (P < 0.01) but did not affect retrograde conduction. Thus, the posterior extension normally contributes to the anterograde but not retrograde recovery curve. Compact node ablation prolonged anterograde conduction (NCTmin increased from 57 +/- 2 ms to 73 +/- 7 ms, P < 0.01) but did not alter ERPN and NCTmax. This ablation abolished retrograde conduction in two preparations and resulted in retrograde slow pathway conduction in four, the latter being interrupted by posterior extension ablation. Thus, the compact node accounts for the baseline of the recovery curve in both directions. Ablation of the compact node results in anterograde slow pathway conduction over the entire cycle length range and may result in retrograde slow pathway conduction.

CONCLUSION

Direction-dependent properties of the AV node arise from those of the compact node-based fast pathway and posterior extension-based slow pathway. Normal AV node has bidirectional dual pathways.

Effects of a blocked atrial beat on the atrioventricular nodal recovery property in patients with dual nodal pathways

Dual AVN physiology can be demonstrated by a variety of maneuvers. To determine whether AVN recovery times following a blocked extrastimulus facilitate or obscure detection of dual AVN physiology, 11 patients (9-17 years) were studied with dual AVN pathways by using single and double atrial extrastimuli. With a single atrial extrastimuli, the premature atrial stimulus (A2) was coupled to basic atrial beats (A1). The fast and slow AVN recovery curves were constructed with plots of the nodal conduction time against the recovery time (A1A2,A2H2). With double atrial extrastimuli, a fixed blocked A2 beat (A2B) was followed by a scanning atrial beat (A3). The nodal recovery property post-A2B was studied by plots of A2BA3,A3H3. In all patients the recovery curve of the fast pathway post-A2B had a leftward shift when compared to that of the pre-A2B curve (i.e., the AH was shortened at the same recovery time). The window of slow pathway conduction post-A2B disappeared totally in five patients and decreased significantly in six patients (post-A2B: 26 +/- 42 ms; pre-A2B: 80 +/- 65 ms, P < 0.05). In the six patients that still had slow pathway conduction post-A2B, the slow pathway effective refractory period post-A2B was significantly less than that of pre-A2B (215 +/- 38 vs 268 +/- 16 ms, P < 0.05). The fast pathway effective refractory period post-A2B was also diminished significantly (235 +/- 62 vs 357 +/- 76 ms, P < 0.0001). The authors conclude that blocked atrial beats decrease the visibility of the slow pathway conduction.

Atrioventricular nodal reentry tachycardia with multiple AH jumps: electrophysiological characteristics and radiofrequency ablation

This article describes the additional use of incremental atrial burst pacing (A1A1) and double atrial extrastimulation with a predefined fast pathway conducted A2 (A1A2A3), rather than single atrial extrastimulation (A1A2) only, to characterize typical atrioventricular nodal reentrant tachycardia (AVNRT). The authors noted an additional 32% of patients had multiple anterograde AV nodal physiology demonstrated when A1A1 or A1A2A3 protocols were deployed compared to more conventional A1A2 protocols. The A2H2max (449 +/- 147 vs 339 +/- 94 ms) and A3H3max (481 +/- 120 vs 389 +/- 85 ms) were higher in 31 patients where multiple jumps in the AV nodal conduction curve were obtained (group 1) compared to 192 patients where only single jump was obtained (group 2) (both P < 0.01). Postablation, the degree of reduction of A2H2max (49%) and A3H3max (50%) in group 1 was greater than in group 2 (38% and 42%, respectively, P < 0.05). In seven of group 1 patients in whom A1A2A3 stimulation was required to reveal multiple jumps, the A2H2max remained unchanged after ablation (237 +/- 89 vs 214 +/- 59, P > 0.05). A3H3max was the only parameter that shortened significantly after ablation. Generally, successful ablation resulted in loss of multiple discontinuities in A1A1/A1H1 or A2A3/A3H3 curves. In conclusion, a combination of A1A2, A1A1, and A1A2A3 are required to fully elucidate AVNRT. Significant shortening of AHmax or loss of multiple jumps after ablation indicates successful elimination of AVNRT in these patients.

Selective atrionodal input ablation for induction of proximal complete heart block with stable junctional escape rhythm in patients with uncontrolled atrial fibrillation

BACKGROUND

The study tests the hypothesis that ablating all inputs to the atrioventricular (AV) node can result in complete heart block with stable junctional escape rhythm.

METHODS AND RESULTS

We attempted atrionodal input ablation in 76 consecutive patients with uncontrolled atrial fibrillation. Fast and slow pathways were first ablated. If there was no AV block, additional energy applications were done between fast and slow pathway locations. The patients were followed for 42 +/- 11 months. Group I (n = 57) comprised patients with complete heart block and junctional escape rhythm (53 +/- 4 beats/min) at the end of the procedure. The escape rhythm remained stable throughout follow-up. Group II (n = 15) were patients who failed the stepwise atrionodal input ablation and required AV junctional ablation guided by His bundle potential to achieve complete heart block. Four patients showed a slow escape rhythm after ablation (33 +/- 4 beats/min). Others had no escape rhythm. All 15 pts remained pacemaker dependent. The total death rate of groups I and II was 18/57 (31.6%) vs 10/15 (66.7%), respectively (p < 0.02). These differences could not be explained by a difference of left ventricular ejection fraction (0.42 +/- 0.07 vs 0.41 +/- 0.04, respectively, p = NS).

CONCLUSIONS

(1) In most patients, ablation of both fast and slow pathways did not result in complete heart block, indicating the presence of multiple atrionodal inputs. (2) Ablation of all atrionodal inputs may result in complete heart block with stable junctional escape rhythm. (3) As compared with AV junctional ablation, atrionodal input ablation was associated with a lower mortality rate on long-term follow up.

Atrioventricular nodal re-entrant tachycardia with two functionally discrete fast pathways

We present a case with two forms of atrioventricular nodal re-entrant tachycardia (AVNRT) that revealed similar H-A-V sequences, but could be differentiated only by their retrograde atrial activation sequences. Both tachycardias were induced following anterograde slow pathway conduction, suggesting the slow pathway as the anterograde limb of the re-entry circuit. The earliest atrial activation site of one form was in the same region of the bundle of His as that of the common type of AVNRT, while that of the other form was the ostium of the coronary sinus. Properly timed extra-stimuli delivered from the atrium or ventricle during the latter tachycardia penetrated through the fast pathway without resetting the tachycardia cycle length. These rare phenomena suggest the existence of two functionally discrete fast pathways, of which the alternative pathway alters to become the more predominant retrograde limb according to time and circumstances.

Patient with atrioventricular node reentrant tachycardia with eccentric retrograde left-sided activation: treatment with radiofrequency catheter ablation

We describe a patient with supraventricular tachycardia with triple atrioventricular (AV) node pathway physiology. A discontinuous curve was present in the antegrade AV nodal function curves. During right ventricular pacing, the earliest retrograde atrial activation was recorded at the left-sided coronary sinus electrode. The retrograde ventricular-atrial interval was long and had decremental conduction. We induced a slow-slow AV node reentrant tachycardia (AVNRT) with eccentric retrograde left-sided activation. After slow pathway ablation, dual AV nodal pathway physiology was present. AVNRT with eccentric retrograde left-sided activation is relatively rare, and our findings suggest that eccentric retrograde left-sided atrial inputs consist partially of a slow pathway and disappear with slow pathway ablation.

Evolution of diagnostic and interventional cardiac electrophysiology: a brief historical review

The field of clinical cardiac electrophysiology has evolved dramatically over the last 30 years, beginning with description of the first His bundle recording in 1969. Subsequently, in the early 1970s, more sophisticated diagnostic electrophysiologic techniques were developed to diagnose and guide drug treatment of arrhythmias. These diagnostic techniques were further advanced during the late 1970s and 1980s to electrically map arrhythmias and guide their surgical ablation. Surgical treatments of both supraventricular and ventricular arrhythmias proliferated in the 1970s and 1980s, with overall excellent results. However, because of the morbidity and mortality associated with arrhythmia surgery, it was ultimately replaced in the 1990s by radiofrequency catheter ablation (RFCA) for treatment of most forms of supraventricular tachycardia and idiopathic ventricular tachycardia, and by the automatic implantable cardioverter defibrillator (ICD) for treatment of life-threatening ventricular arrhythmias associated with coronary artery disease and dilated cardiomyopathy. At present, the only arrhythmias that cannot be reliably and safely cured by RFCA are chronic atrial fibrillation and life-threatening ventricular arrhythmias. For chronic atrial fibrillation, new catheter designs are being developed to create linear ablation lines mimicking the curative MAZE operation. For life-threatening ventricular arrhythmias, the ICD has been increasingly utilized as transvenous lead systems and smaller devices have been developed. In the next millennium, new developments that may be expected for treatment of atrial fibrillation and life-threatening ventricular arrhythmias include catheter systems for linear RFCA of atrial fibrillation, ICDs for both atrial and ventricular defibrillation, and biventricular pacing ICDs for patients with congestive heart failure.

Double component action potentials in the posterior approach to the atrioventricular node: do they reflect activation delay in the slow pathway?

OBJECTIVES

The aim of the study was to elucidate the mechanism of double component action potentials in the posterior approach to the atrioventricular (AV) junctional area.

BACKGROUND

Double component action potentials are often associated with activation delay and therefore might be a marker of the location of the so-called slow pathway.

METHODS

The AV junction was scanned for double component action potentials in Langendorff perfused pig and dog hearts, using conventional microelectrode recordings. Characteristics of these action potentials were investigated during basic and premature stimulation and cooling of the anterior approach to the node.

RESULTS

During basic stimulation, double component action potentials were recorded in 19 out of 20 hearts. In 74% of these cases, the second component occurred before the His deflection. During premature stimulation this percentage was 50%, while delay between the two components always increased. In 80% of the cases, the amplitude of the two components became <20 mV during progressive shortening of the coupling interval. The first component was generated by activation in superficial layers, the second one by activation in deeper layers. Cooling of the anterior region revealed that the second component was caused by activation arriving from the anterior region.

CONCLUSIONS

Double component action potentials in the posterior approach to the AV node are generated by the asynchronous arrival of wave fronts in different, weakly coupled layers or by the summation of asynchronously arriving wave fronts. They are not always associated with activation delay in the slow pathway.

Characteristics, circuit, mechanism, and ablation of reentry in the rabbit atrioventricular node

INTRODUCTION

The circuitry underlying AV nodal reentry remains debated. We developed a model of AV nodal reentry and assessed the role of nodal inputs, compact node, and its posterior nodal extension (PNE) in this phenomenon.

METHODS AND RESULTS

A fine scanning of short coupling interval range with an atrial premature beat consistently initiated slow-fast AV nodal reentrant beats that occurred 37+/-31 msec (mean+/-SD) after His-bundle activation in 11 of 16 consecutive rabbit heart preparations. The repeated testing (>40 times) of a chosen coupling interval within reentry window (6+/-9 msec, n = 11) yielded reentrant intervals that varied by 2+/-1 msec (mean SD for 40 beats+/-SD, n = 11). The breakthrough point of reentrant activation, as assessed from four perinodal sites, varied in different preparations from diffuse (4) to anterior (1), medial (3), or posterior (3); mean reentrant interval did not differ between perinodal sites. Antegrade perinodal activation pattern did not differ at reentrant versus nonreentrant coupling intervals and thus was not a primary determinant of reentry. A PNE ablation (n = 4) interrupted the slow pathway conduction and prevented reentry without affecting antegrade perinodal activation or fast pathway conduction.

CONCLUSION

A reproducible model of AV nodal reentrant beats was developed and used to study underlying circuitry. The AV nodal reentry involves unaltered antegrade perinodal activation, slow PNE conduction and retrograde broad invasion of perinodal tissues starting at a preparation-dependent breakthrough point. A PNE ablation abolishes the reentry.