Characterization of atrioventricular nodal reentry with continuous atrioventricular node conduction curve by double atrial extrastimulation

A jump in the atrioventricular conduction curve is not caused by a switch from fast pathway to slow pathway conduction

Background: A jump in the atrioventricular (AV) conduction curve is the current clinical criterion of dual-pathway electrophysiology. However, the assumption that a jump indicates a switch from fast pathway (FP) to slow pathway (SP) conduction remains unconfirmed. This study was carried out to investigate whether a jump indeed indicates a transition from FP to SP conduction, and if not, what the potential cause is. Methods: Eighty-one experimental records from rabbit AV nodal preparations containing the following data were analyzed: 1) had at least one AV conduction curve and 2) had recording of His electrogram alternans (a validated new index of dual-pathway conduction). Most cases also had intracellular action potential recordings from the AV nodal fibers. Results: Of the 81 preparations, 11 (13%) showed a jump in the AV conduction curve. The jumps always occurred after the FP to SP transition. The FP-SP transition occurred at prematurity at 196 ± 39 ms versus the jump at 114 ± 13 ms (p < 0.001). The beat with a jump showed an SP-FP pattern in seven and an SP-SP pattern in four preparations. The jumps were always associated with and most likely caused by the formation of intranodal/nodal-atrial reentry and its subsequent conduction, rather than a switch from FP to SP conduction. Conclusion: Contrary to what has been assumed, a transition from FP to SP conduction does not produce a jump in the AV conduction curve. A jump in the AV conduction curve is most likely caused by the formation of intranodal/nodal-atrial reentry and its subsequent conduction.

A unified theory for the circuit of atrioventricular nodal re-entrant tachycardia

Atrioventricular nodal re-entrant tachycardia (AVNRT) is the most common regular tachycardia in the human, but its exact circuit remains elusive. In this article, recent evidence about the electrophysiological characteristics of AVNRT and new data on the anatomy of the atrioventricular node, are discussed. Based on this information, a novel, unified theory for the nature of the circuit of the tachycardia is presented.

[Mapping and ablation of cardiac arrhythmias : Never forget where you are coming from]

With the rapid development of new mapping and imaging technologies as well as catheter ablation technologies, it is increasingly important to understand the basic concepts of conventional mapping and ablation of cardiac arrhythmias. Prerequisite for successful ablation is the exact identification of the tachycardia mechanism and subsequent localization of the origin or tachycardic substrate. Only intracardiac electrograms provide decisive information regarding activation time and signal morphology. In some arrhythmias, it is necessary to supplement conventional mapping with so-called pace and/or entrainment mapping. This article aims to discuss and demonstrate the fundamentals of intracardiac mapping as it relates to the mapping and ablation of supraventricular and ventricular arrhythmias based on representative clinical cases. Modern three-dimensional mapping methods make it possible to individually optimize established ablation strategies with significantly better spatial resolution. The authors aimed to demonstrate that intracardiac uni- and bipolar electrograms provide essential information about timing and morphology guiding successful catheter ablation. Furthermore, our article provides useful information about conventional cardiac mapping techniques including activation mapping, pace mapping, and individual substrate mapping.

Novel electrophysiological characteristics of atrioventricular nodal continuous conduction curves in atrioventricular nodal re-entrant tachycardia with concomitant cavotricuspid isthmus-dependent atrial flutter

AIMS

The detailed electrophysiological characteristics of patients with both atrioventricular nodal re-entrant tachycardia (AVNRT) and atrial flutter (AFL) have not been clarified. This study investigated the related electrophysiological differences in a large series of patients undergoing radiofrequency catheter ablation of AVNRT.

METHODS AND RESULTS

A total of 1063 clinically documented AVNRT patients underwent catheter ablation were enrolled. Before the slow pathway (SP) ablation, 61 patients (5.7%) had inducible sustained cavotricuspid isthmus (CTI)-dependent AFL (Group 1), and the others (94.3%) without inducible sustained CTI-dependent AFL were defined as Group 2. The electrophysiological characteristics of these two groups and effect of the SP ablation on the inducibility of AFL were assessed. In Group 1, 36 patients (59%) had inducible/sustained AFL after the ablation of AVNRT and required a CTI ablation. The Group 1 patients had more AVNRT with continuous atrioventricular (AV) node function curves (P < 0.001, odds ratio = 7.55 [3.70-16.7], multivariate regression), and a younger age (P = 0.02, odds ratio = 1.02 [1.003-1.03], multivariate regression) than Group 2. The other characteristics were comparable between the two groups. The long-term follow-up (64.9 ± 34.9 months) revealed that the recurrence of AFL/atrial fibrillation was similar between the two groups (P > 0.05).

CONCLUSION

Atrioventricular nodal re-entrant tachycardia patients with concomitant CTI-dependent AFL had more continuous AV node function curves. Forty-one per cent of these patients had non-inducible AFL after the SP ablation, indicating a slow conduction isthmus in the triangle of Koch area.

In vivo recording of Zhang's phenomenon (His electrogram alternans): a novel index of atrioventricular node dual pathway conduction

BACKGROUND

Zhang's phenomenon (originally His electrogram alternans) is a new index of atrioventricular node dual pathway electrophysiology. This index has been described and validated in isolated hearts in vitro, but has not been recorded in vivo.

METHODS

This study explored the feasibility of in vivo recording of Zhang's phenomenon (His electrogram alternans) in six dogs with a custom-built bipolar electrode.

RESULTS

The His electrogram recorded from superior His bundle domain (superior His electrogram) was high in amplitude at basic beats and long coupling intervals (i.e., fast pathway conduction) and low amplitude at short prematurities (i.e., slow pathway conduction). In contrast, His electrogram recorded from the inferior His bundle domain (inferior His electrogram) was always from low amplitude during fast pathway conduction to high amplitude during slow pathway conduction. The characteristic His electrogram alternans had been recorded in vivo in all six animals.

CONCLUSIONS

This study provided the first data representing in vivo recording of Zhang's phenomenon (His electrogram alternans) in large animals. Clinical studies are needed before this novel index can be applied in patients.

The atrioventricular nodal reentrant tachycardia circuit: A proposal

Several models of the atrioventricular nodal reentrant tachycardia circuit have been proposed. Recently, there has been experimental and clinical electrophysiology evidence that the right and left inferior extensions of the human atriventricular node and the atrionodal inputs they facilitate may provide the anatomic substrate of the slow pathway. Inferior nodal extensions appear to constitute a necessary limb of the tachycardia circuit in all forms of atrioventricular nodal reentrant tachycardia and represent the ablation target for all forms of this arrhythmia. Anatomic variations of multiple atrionodal inputs via atrial transitional cells may create the conditions for tachycardia inducibility and differing patterns of retrograde atrial activation. In the present article, we summarize the available evidence and propose a comprehensive model of the tachycardia circuit for all forms of atrioventricular nodal reentrant tachycardia based on the concept of atrionodal inputs.

Unified rate-dependent atrioventricular nodal function: Consistent recovery and fatigue properties revealed with S1S2S3 protocols and different recovery indexes

BACKGROUND

Rate-dependent nodal properties are commonly assessed with premature protocols performed at different basic rates. Because characteristics of responses differ with recovery time index, the true nature of nodal rate-dependent properties is elusive.

OBJECTIVES

The purpose of this study was to reveal consistent nodal rate-dependent properties regardless of selected recovery index.

METHODS

With S(1)S(2)S(3) protocols, we independently varied basic and pretest cycle lengths and thereby distinguished cumulative from noncumulative effects of rate on nodal conduction time in rabbit heart preparations. Nodal responses to 30 basic and pretest cycle length combinations (five with identical basic and pretest cycles as in standard protocols) were analyzed using both atrial (AA) and His-atrial (HA) intervals as recovery index.

RESULTS

AA and HA curves had an identical shape for any of 30 steady-state conditions. When assessed with constant pretest cycle lengths, cumulative effects (fatigue) of shortened basic cycle lengths were also independent of recovery index. Shortening of pretest cycle length at fixed basic rates led to apparent inhibitory and facilitatory effects when assessed with AA and HA curves, respectively. These effects vanished when a single long cycle was inserted after the pretest cycle. In all responses including those obtained with standard protocols, combined effects of basic and pretest cycle lengths set nodal conduction time.

CONCLUSION

S(1)S(2)S(3) protocols reveal consistent nodal recovery and fatigue properties regardless of recovery index used. Changes in nodal function curves arising from the use of different recovery indexes mainly depend on pretest effects. This study provides a new approach to a unified interpretation of nodal recovery and fatigue properties.

Classification and differential diagnosis of atrioventricular nodal re-entrant tachycardia

Recent evidence on atrioventricular nodal re-entrant tachycardia has identified several types of this common arrhythmia, with potential therapeutic implications. This article reviews the relevant new information, discusses the differential diagnosis of atrioventricular nodal re-entrant tachycardia, and summarizes the electrophysiological criteria for classification of the various forms of the arrhythmia.

Slow pathway modification for atrioventricular nodal reentrant tachycardia

The change in the "refractory window" was assessed as a possible indicator of successful slow pathway modification in 26 pediatric patients with persistent dual-atrioventricular node physiology. The "refractory window" was defined as the difference between the fast and slow pathway effective refractory periods. A significant decrease in the refractory window (p <0.001) after successful slow pathway modification was found.

Right and left inferior extensions of the atrioventricular node may represent the anatomic substrate of the slow pathway in humans

OBJECTIVES

The purpose of this study was to investigate the electrophysiologic characteristics of the inferior extensions of the human atrioventricular (AV) node and their possible relationship to slow pathway conduction.

BACKGROUND

The human heart contains right and left inferior extensions of the AV node that relate to right and left atrial inputs.

METHODS

Fourteen patients admitted for catheter ablation of left-sided accessory pathways were studied. Atrial pacing was performed from multiple sites in both atria, and simultaneous His-bundle recordings from right and left sides of the septum were made.

RESULTS

Significant differences of A-H and stimulus to His (St-H) intervals with pacing at various sites were found. St-H intervals were similar during constant pacing from the low right atrium or the left inferoparaseptal area (112 +/- 28 ms vs 112 +/- 26 ms, P = .8, for right His recordings and 114 +/- 23 ms vs 111 +/- 25 ms, P = .9, for left His recordings). At maximum decrement, there were significantly shorter St-H intervals during left inferoparaseptal pacing compared to low right atrial pacing (201 +/- 24 ms vs 218 +/- 44 ms, P = .02, for right His recordings, and 200 +/- 24 ms vs 219 +/- 41 ms, P = .009, for left His recordings). Differences on right His recordings between St-H intervals at maximum decrement and at constant pacing from the low right atrium were significantly higher than corresponding differences on left His recordings during pacing from the left inferoparaseptal area (P = .035).

CONCLUSIONS

Our findings support the concept that the right and left inferior extensions of the human AV node may represent the anatomic substrate of the slow pathway as defined electrophysiologically.

Electrophysiological characteristics of accessory pathways with prolonged retrograde conduction

Electrophysiological characteristics of an accessory pathway (AP) with a long ventriculoatrial (VA) interval (arbitrarily defined as > or = 50 ms and absence of continuous electrical activity) and no retrograde decremental property are described in this study. Fifteen patients (group 1) were compared with 171 patients with normal VA conduction (group 2). Mean VA conduction time was 77 +/- 24 versus 34 +/- 12 ms in group 1 versus group 2, respectively. Group 1 patients were older (55 +/- 14 vs 40 +/- 14 years), the male to female ratio was higher (2.8 vs 1.6), and APs were more prevalent on the right (60%) but manifest APs were lower (20% vs 54%) compared to group 2 patients (P < 0.05 in all cases). QRS morphology during induced atrioventricular reciprocating tachycardia was identical in both groups but the tachycardia cycle length was longer in group 1 (373 +/- 29 vs 344 +/- 50 ms, P < 0.05). Retrograde AP block cycle length and effective refractory period were greater in group 1 (362 +/- 59 vs 293 +/- 57 ms; 330 +/- 58 vs 273 +/- 55 ms, both P < 0.05). Adenosine (up to 18 mg) and verapamil (5-10 mg) failed to block the VA conduction via AP during ventricular pacing. In group 1 the number of radiofrequency lesions for a successful ablation were significantly less (3 +/- 2 vs 6 +/- 5, P < 0.05). In conclusion, APs with a long VA interval and no decremental retrograde conduction have electrophysiological characteristics that are different from those with a short VA interval. Role of aging deserves further exploration.

Electrophysiology of inducible atrial flutter in patients with atrioventricular nodal reentrant tachycardia

An association between atrial flutter and atrioventricular nodal reentrant tachycardia (AVNRT) has been observed, but the underlying mechanisms are poorly defined. This issue was therefore investigated by comparing the electrophysiological properties of AVNRT patients with and without inducible atrial flutter and those of patients with a history of flutter. Twenty-nine patients with clinically documented atrial flutter and 104 with AVNRT were studied. Atrial flutter was induced in 38 (37%) AVNRT patients during standardized electrophysiological testing before radiofrequency ablation. The atrial relative refractory periods in AVNRT patients with inducible flutter (260 +/- 30 ms) were significantly shorter than those of either patients with a history of flutter (282 +/- 30 ms; P = 0.02) or AVNRT patients without inducible flutter (284 +/- 38 ms; P = 0.006). The atrial effective refractory periods in AVNRT patients with inducible flutter (205 +/- 31 ms) were shorter than in AVNRT patients without inducible flutter (227 +/- 40 ms; P = 0.01). The maximum AH interval during premature atrial stimulation in patients with clinical flutter (239 +/- 94 ms) was shorter than in AVNRT patients either with (290 +/- 91 ms; P = 0.04) or without inducible flutter (313 +/- 101 ms; P = 0.002). However, no significant differences were found in the maximum AH interval achieved during incremental atrial pacing among different groups. Our data show that a non-clinical flutter could more often be induced in those who had short atrial refractoriness. Despite their anatomical proximity, the slow pathway conduction of AVNRT and the isthmus slow conduction of flutter may be related to different mechanisms.

Prediction of Clinical Recurrence of Atrioventricular-Nodal Reentrant Tachycardia (AVNRT) After Successful Slow Pathway Ablation

BACKGROUND

Even after successful slow pathway (SP) ablation for atrioventricular-nodal reentrant tachycardia (AVNRT), there may be clinical recurrence in certain patients and it is clinically important to be able to predict that.

METHODS AND RESULTS

In 97 patients with common type AVNRT, the effective refractory period (ERP) of the fast pathway (FP), SP-ERP, and prolongation of the atrio-His (AH) interval (AH) at the time of jump-up phenomenon were investigated. In patients with residual SP, parameters were re-evaluated in a similar manner. SP was successfully ablated and AVNRT was not inducible in all the patients, but residual SP was observed in 54 of the 97 patients, and there was late clinical recurrence in 10 patients (10/54 patients with residual SP and 0/43 without residual SP, p=0.002). The changes in FP-ERP before and after ablation (DeltaFP-ERP) did not differ between recurrent and non-recurrent patients. Among the patients with residual SP, DeltaSP-ERP did not differ between the groups. However, the changes in DeltaAH before and after ablation (DeltaDeltaAH) were larger in non-recurrent (24+/-30 ms) than in the recurrent patients (4+/-7 ms, p=0.042).

CONCLUSIONS

In patients with AVNRT, the residual SP and changes in DeltaAH after successful SP ablation might be useful indices of clinical recurrence.

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.

Determination of repetitive slow pathway conduction for evaluation of the efficacy of radiofrequency ablation in AVNRT

AIMS

To determine whether the loss of repetitive slow pathway conduction identifies a successful radiofrequency ablation of atrioventricular nodal reentry tachycardia (AVNRT).

METHODS AND RESULTS

Thirty nine consecutive patients undergoing ablation of AVNRT using the slow pathway approach were included. At baseline and after each radiofrequency application with an episode of junctional rhythm, repetitive slow pathway conduction was assessed as follows: Effective refractory period of the fast pathway was determined. The coupling interval of the first atrial extrastimulus (A2) was set at 30 ms below the effective refractory period of the fast pathway to ensure its conduction via the slow pathway. The second atrial extrastimulus (A3) was introduced at progressively longer coupling intervals starting from 200 ms until: (1) it propagated to the His bundle or (2) an anterogradely blocked AV nodal echo of A2 appeared before a conducted A3 depolarized the atrium in the His bundle electrogram. The response was termed repetitive slow pathway conduction if A3 was conducted with an AH > 200 ms. Application was considered successful if no AVNRT could be induced. Repetitive slow pathway conduction was present after 1 of 39 successful and after 34 of 40 ineffective applications (P < 0.0001). Repetitive slow pathway conduction identified a successful application with 97% sensitivity, 86% specificity, 86% positive predictive value, and 97% negative predictive value.

CONCLUSION

The presence of repetitive slow pathway conduction identifies an unsuccessful application with a clinically meaningful negative predictive value.

The tendons of Todaro and the "triangle of Koch": lessons from eponymous hagiolatry

INTRODUCTION

There is growing use of the Todaro tendon and triangle of Koch as anatomic icons for invasive cardiac electrophysiologists. Reasons exist to doubt this validity.

METHODS AND RESULTS

Histologic sections were prepared from 96 anatomically normal human hearts. The study area extended from the crista supraventricularis to the eustachian valve and included the AV node and His bundle. This encompasses any tendon of Todaro. Because the purported triangle of Koch includes the tendon of Todaro, all of Koch's available publications were examined. The tendon of Todaro is absent in only one fourth of infant hearts, but in two thirds of adult hearts. Tendons present were less often single than double or more, rarely exceeded 4 mm in length, and were seldom > 1 mm in diameter. Tendons usually originated from the central fibrous body and ended in the eustachian valve. Their origin most often was over the His bundle or its junction with the AV node, rather than the AV node. Tendons were primarily composed of collagen. Koch never described any triangle or acknowledged existence of tendons of Todaro.

CONCLUSION

Todaro tendons are too often absent (or multiple) to warrant use as anatomic landmarks. Without this side of the supposed triangle of Koch, the entire tendon and triangle concept collapses and should be abandoned. There are numerous far more constant anatomic landmarks available to orient one to the human AV node and His bundle; these are briefly reviewed.