Coexistent Mahaim and Kent accessory connections: diagnostic and therapeutic implications

Variable clinical features and ablation of manifest nodofascicular/ventricular pathways

BACKGROUND

Manifest nodofascicular/ventricular (NFV) pathways are rare.

METHODS AND RESULTS

From 2008 to 2013, 4 cases were identified with manifest NFV pathways from 3 centers. The clinical findings and ablation sites are reported. All 4 cases presented with a wide complex tachycardia but with different QRS morphologies. Case 1 showed a left bundle branch block/superior axis, case 2 showed a right bundle branch block/inferior axis, case 3 showed a left bundle branch block/inferior axis, and case 4 showed a narrow QRS tachycardia and a wide complex tachycardia with a left bundle branch block/inferior axis. Three of the 4 tachycardias had atrioventricular dissociation ruling out extranodal accessory pathways, including atriofascicular pathways. Programmed extrastimuli showed evidence of a decremental accessory pathway in 3 of the 4 cases. Coexisting tachycardia mechanisms were seen in 3 of the 4 cases (atrioventricular nodal reentry tachycardia [2] and atrioventricular reentrant tachycardia [1]). Ablation in the slow pathway region eliminated the NFV pathway in 3 (transient in 1) with the other responding to surgical closure of a large atrial septal defect. The NFV pathway was a critical part of the tachycardia circuit in 1 and proved to be a bystander in the other 3 cases.

CONCLUSIONS

Manifest NFV pathways presented with variable QRS expression dependent on the ventricular insertion site and often coexisted with other tachycardia mechanisms (atrioventricular nodal reentry tachycardia and atrioventricular reentrant tachycardia). In most cases, the atrial insertion of the pathway was in or near the slow pathway region. The NFV pathways were either critical to the tachycardia circuit or served as bystanders.

Parasystole in a mahaim accessory pathway

Automaticity has been described in Mahaim pathways, both spontaneously and during radiofrequency ablation. We describe an unusual case of automatic rhythm from a Mahaim pathway presenting as parasystole. The parasystolic beats were also found to initiate tachycardia, resulting in initial presentation with incessant tachycardia and tachycardia induced cardiomyopathy.

Differentiating fasciculoventricular pathway from Wolff-Parkinson-White syndrome by electrocardiography

BACKGROUND

In school-based cardiovascular screening programs in Japan, Wolff-Parkinson-White (WPW) syndrome is diagnosed based on the presence of an electrocardiographic (ECG) delta wave without differentiation from the fasciculoventricular pathway (FVP), although the risk of sudden death is associated only with the former.

OBJECTIVE

The purpose of this study was to differentiate FVP patients among children diagnosed with WPW syndrome by ECG.

METHODS

Children who were diagnosed with WPW syndrome through school screening between April 2006 and March 2008 and had QRS width ≤120 ms were included. Patients with asthma and/or coronary heart disease were excluded. FVP and WPW syndrome were differentiated based on ECG responses to adenosine triphosphate (ATP) injection. Age, PR interval, QRS width, and Rosenbaum classification were compared among patients.

RESULTS

Thirty patients (median age 12.7 years, range 6.5-15.7 years) participated in the study. FVP was diagnosed in 23 patients (76.7%), and WPW syndrome in 7 (23.3%). In Rosenbaum type A patients, all six patients had WPW syndrome, whereas FVP was diagnosed in 23 of 24 and WPW syndrome was diagnosed in 1 of 24 of type B patients. Age, PR interval, and QRS width were not significantly different between the two conditions.

CONCLUSION

ATP stress test was reliable in differentiating FVP from WPW syndrome. Although FVP is considered rare, the results of our study indicate that many WPW syndrome patients with QRS width ≤120 ms may actually have FVP. Patients categorized as type B are more likely to have FVP, whereas type A patients are most likely to have WPW syndrome.

Clinical and electrophysiological characteristics of fasciculoventricular fibers in children

INTRODUCTION

Fasciculoventricular (FV) fiber is a rare cause for ventricular preexcitation. It is usually described as an innocent bystander pathway. There is only limited data on FV fiber in children. Hence we evaluated the clinical and electrophysiological features of FV fiber in a group of 11 children.

METHODS AND RESULTS

Of 215 children with manifest preexcitation who had electrophysiological studies at the University of Miami, 11 (5.1%) had characteristics of FV fiber. FV fiber was not directly responsible for any arrhythmias in these children. Three children had supraventricular tachycardia due to associated left sided Kent fiber and FV fiber was identified after the ablation of Kent fiber. One child had associated hypertrophic cardiomyopathy, another child had atrial septal defect and a third child had ventricular septal defect. The electrophysiological testing of FV fiber revealed AH interval of 40-95 ms and H-delta interval of 15-40 ms. Mapping study showed that the FV fiber was located on the right side of the heart in all patients: right anteroseptal in 9, right midseptal in 1 and it could not be mapped well in 1 as the delta wave was intermittent. We identified a discrete FV fiber depolarization spike in 9 patients, with a local FV fiber depolarization to delta wave interval of 5-20 ms (11+4 ms).

CONCLUSION

FV fiber is an uncommon cause for ventricular preexcitation in children and it can be associated with other conduction abnormalities and heart defects. FV fibers are commonly located at the right anteroseptal region and are not usually involved in any tachycardia. Discrete local FV fiber potential can be identified during electrophysiological testing of these patients.

Anatomic and electrophysiologic evaluation of a right lateral atrioventricular Mahaim fiber

We report a patient who underwent an electrophysiologic study and radiofrequency catheter ablation for a right lateral Mahaim fiber. During sinus rhythm with overt preexcitation, propagation mapping was performed in the right ventricle using a three-dimensional electro-anatomical mapping system (CARTO). Small discrete potentials, which reflected the excitation of the Mahaim fiber, could be recorded along the line from the vicinity of the parental tricuspid annulus to approximately one-third of distal site from the base to the apex. The relationship of the timing of its potential to the anatomical location could be disclosed on recordings of the local electrogram and anatomical map.

Unusual QRS Morphology on ECG: A Rare Condition and an Interesting Response to Pacing

We present the interesting case of a young man with borderline wide QRS complexes noted on electrocardiogram (ECG). The diagnosis of an unusual form of preexcitation was reached using observations from intracardiac tracings at electrophysiology study. Atrial pacing consistently resulted in further widening of the first conducted QRS complex, and the physiology underlying this unusual finding is explored.

Narrow QRS Tachycardia with Ventriculoatrial Dissociation Mediated by a Left Fasciculoventricular Fiber

A 30-year-old man presented with narrow QRS tachycardia. The intracardiac electrocardiogram showed an atrial-HIS (AH) interval of 75 msec and a HIS-ventricular (HV) interval of 44 msec during baseline. Atrial incremental pacing revealed HV shortening, with apparent incomplete right bundle branch block (RBBB) morphology without QRS complex axis deviation. The induced tachycardia exhibited several QRS morphologies: a narrow QRS, complete RBBB and complete left bundle branch block (LBBB) morphology. Spontaneous conversion of the QRS pattern from wide to narrow was observed. The cycle length of the tachycardia was significantly shortened (from 316 to 272 ms) from LBBB morphology to narrow QRS complex. The atrial activation was dissociated from the ventricular activation during all tachycardias. Each QRS complex during tachycardia was preceded by a HIS deflection and HV interval was 35 ms, which was shorter than that of sinus rhythm. HIS deflection was earlier than right bundle potential during all kinds of tachycardia. This tachycardia is most likely mediated by a left fasciculoventricular fiber which connects the HIS bundle below the atrioventricular node to the myocardial tissue of the left ventricle. The HIS-Purkinje system is used as an antegrade conduction limb and the fasciculoventricular fiber as a retrograde limb in the tachycardia circuit.

Electrocardiographic Characteristics of Fasciculoventricular Pathways

INTRODUCTION

Fasciculoventricular (FV) pathways are rare variants of preexcitation, and their ECGs may be misinterpreted as Wolff-Parkinson-White syndrome with anteroseptal accessory pathways (WPW-AS). We analyzed the electrocardiographic characteristics of the patients with FV pathways to find out the different findings from WPW-AS.

METHODS AND RESULTS

Five patients with FV pathways and four patients with WPW-AS who underwent electrophysiologic studies were evaluated. Intervals and amplitudes of each wave and QRS morphologies were analyzed in standard 12-lead ECGs of these patients by two independent cardiologists without the information of the electrophysiologic findings. PR intervals were longer in FV pathways (122 +/- 11.0 vs 83 +/- 21 ms, FV pathways vs WPW-AS, P = 0.017). In lead V1, narrower width of R waves (25 +/- 6 vs 45 +/- 13 ms, P = 0.037) and smaller amplitude of S waves (12.8 +/- 8.3 vs 26.6 +/- 7.4 mm, P = 0.037) were observed in FV pathways. The polarity of delta waves in V1 was flat or negative in contrast with the cases of WPW-AS in which the polarity was positive. Three of five patients had notching in the descending limb of S waves in V1, which was not observed in WPW-AS.

CONCLUSION

FV pathways have different ECG characteristics from WPW-AS in PR interval and morphology of QRS complexes in lead V1 of the standard 12-lead ECG.

Fasciculoventricular Pathways:

Fasciculoventricular Fibers.

INTRODUCTION

Fasciculoventricular tracts are considered a rare form of ventricular preexcitation. Few fasciculoventricular pathways have been reported, and none have been linked to a reentrant tachycardia.

METHODS AND RESULTS

Four patients with fasciculoventricular bypass tracts underwent electrophysiologic evaluation. Two patients had a single fasciculoventricular pathway, one that inserted anteroseptally and the other in the left ventricle. Two patients also had an AV bypass tract, with anterograde conduction over the fasciculoventricular pathway during orthodromic AV reentrant tachycardia. After ablation of the AV pathways, the ECG during sinus rhythm and the electrophysiologic study showed ventricular preexcitation due to a fasciculoventricular bypass tract inserting into the right ventricle. Adenosine triphosphate was helpful in the diagnostic process.

CONCLUSION

Electrophysiologists should be able to make the differential diagnosis between a fasciculoventricular bypass tract and an anteroseptal accessory pathway to preclude potential harm to the AV conduction system if a fasciculoventricular pathway is targeted for catheter ablation.

Coexistent atrioventricular and nodoventricular pathways in a patient with hypertrophic cardiomyopathy

A 17-year-old girl with concentric hypertrophic cardiomyopathy presented with a wide complex tachycardia and underwent electrophysiological study. She was found to have an antidromic tachycardia utilizing a decremental atrioventricular fiber as the anterograde limb with retrograde conduction occurring through the septum. Ablation of a right free-wall pathway rendered tachycardia noninducible, yet ventricular preexcitation remained. After ablation there was evidence of a second nodoventricular connection. We believe this to be the first report of coexistent "Mahaim" fibers; one a decremental atrioventricular connection and the second nodoventricular.

Electrophysiologic characteristics and radiofrequency ablation of concealed nodofascicular and left anterograde atriofascicular pathways

INTRODUCTION

True nodoventricular or nodofascicular pathways and left-sided anterograde decremental accessory pathways (APs) are considered rare findings.

METHODS AND RESULTS

Two unusual patients with paroxysmal supraventricular tachycardia were referred for radiofrequency (RF) ablation. Both patients had evidence of dual AV nodal conduction. In case 1, programmed atrial and ventricular stimulation induced regular tachycardia with a narrow QRS complex or episodes of right and left bundle branch block not altering the tachycardia cycle length and long concentric ventriculoatrial (VA) conduction. Ventricular extrastimuli elicited during His-bundle refractoriness resulted in tachycardia termination. During the tachycardia, both the ventricles and the distal right bundle were not part of the reentrant circuit. These findings were consistent with a concealed nodofascicular pathway. RF ablation in the right atrial mid-septal region with the earliest atrial activation preceded by a possible AP potential resulted in tachycardia termination and elimination of VA conduction. In case 2, antidromic reciprocating tachycardia of a right bundle branch block pattern was considered to involve an anterograde left posteroseptal atriofascicular pathway. For this pathway, decremental conduction properties as typically observed for right atriofascicular pathways could be demonstrated. During atrial stimulation and tachycardia, a discrete AP potential was recorded at the atrial and ventricular insertion sites and along the AP. Mechanical conduction block of the AP was reproducibly induced at the annular level and at the distal insertion site. Successful RF ablation was performed at the mitral annulus.

CONCLUSION

This report describes two unusual cases consistent with concealed nodofascicular and left anterograde atriofascicular pathways, which were ablated successfully without impairing normal AV conduction system.

Left posteroseptal Mahaim fiber associated with marked longitudinal dissociation

We report a patient who underwent radiofrequency catheter ablation of a left posteroseptal atrioventricular (AV) Mahaim fiber with a marked longitudinal dissociation. During atrial pacing, Wenckebach-type atrioventricular block over the accessory pathway was observed with progressive preexcitation and no change in polarity of the delta waves. The AV conduction curve was discontinuous, with a distinct "jump-up" in local AV conduction time of 84 ms. The earliest ventricular activation was recorded from the posteroseptal portion of the mitral annulus, and the unipolar electrogram from a distal electrode had a high, steep deflection with uniphasic QS-like activity with 62 ms of local AV conduction time.

Right posterior atrioventricular ring: a location for different types of atrioventricular accessory connections

We present an unusual case of a 28-year-old female patient with recurrent episodes of tachycardias due to participation of two accessory connections located in the posterior tricuspid annulus. Both connections were of the atrioventricular type, the one with non decremental fast conducting properties at the right posteroseptal area, the other with node-like properties at the posterolateral tricuspid ring. Both pathways were successfully ablated transvenously with radiofrequency energy application at the same session. Implications about a common embryological origin of the two pathways as well as review of the literature for similar cases are presented.

Radiofrequency ablation of a concealed nodoventricular Mahaim fiber guided by a discrete potential

INTRODUCTION

We present the case of a 17-year-old woman who underwent an electrophysiological study and radiofrequency (RF) ablation of supraventricular tachycardia refractory to medical treatment. Two right-sided, concealed, nondecremental atrioventricular accessory pathways (AV-APs) involved in orthodromic circus movement tachycardias were identified. After RF ablation of both AV-APs, evidence of bidirectional dual AV nodal conduction was demonstrated and regular narrow complex tachycardia was induced.

METHODS AND RESULTS

During the tachycardia, retrograde slow and fast AV nodal pathway conduction with second-degree ventriculoatrial (VA) block and VA dissociation were observed. During the tachycardia with second-degree VA block, ventricular extrastimuli elicited during His-bundle refractoriness advanced the next His potential or terminated the tachycardia. Mapping the right atrial mid-septal region, a distinct high-frequency activation P potential was recorded in a discrete area, two thirds of the way from the His bundle toward the os of the coronary sinus. Detailed electrophysiologic testing with the recordable P potential demonstrated that the tachycardia utilized a concealed nodoventricular AP arising from the proximal slow AV nodal pathway.

CONCLUSION

The tachycardia with slow 1:1 VA conduction could be reset by ventricular extrastimuli elicited during His-bundle refractoriness advancing the subsequent activation P potential and atrial activation. RF ablation guided by recording of the activation P potential resulted in elimination of both the slow AV nodal pathway and the nodoventricular connection with preservation of the normal AV conduction system.

Preexcitation secondary to fasciculoventricular pathways in children: a report of three cases

INTRODUCTION

Fasciculoventricular connections are the rarest form of accessory pathways leading to preexcitation. Electrophysiologic characteristics of these pathways include ventricular preexcitation with normal PR and AH intervals and short HV intervals during sinus rhythm. In addition, atrial overdrive pacing prolongs the PR interval without affecting the HV interval or the degree of preexcitation.

METHODS AND RESULTS

From March 1994 through February 1997, 3 of 59 pediatric patients referred for electrophysiologic study for preexcitation on surface ECGs were found to have fasciculoventricular pathways. Two patients had no inducible supraventricular tachycardia. One patient had successful ablation of both a left lateral pathway and a concealed anterolateral pathway that had facilitated antidromic and orthodromic supraventricular tachycardias, respectively.

CONCLUSION

Children often manifest minimal preexcitation via accessory AV pathways due to rapid AV conduction and/or left lateral pathway location. Fasciculoventricular pathways may masquerade as Wolff-Parkinson-White syndrome. Separation of the two diagnoses depends on the demonstration of specific electrophysiologic criteria.

Narrow complex tachycardia with VA block: diagnostic and therapeutic implications

To review our experience with cases of narrow complex tachycardia with VA block, highlighting the difficulties in the differential diagnosis, and the therapeutic implications. Prior reports of patients with narrow complex tachycardia with VA block consist of isolated case reports. The differential diagnosis of this disorder includes: automatic junctional tachycardia, AV nodal reentry with final upper common pathway block, concealed nodofascicular (ventricular) pathway, and intra-Hissian reentry. Between June 1994 and January 1996, six patients with narrow complex tachycardia with episodes of ventriculoatrial block were referred for evaluation. All six patients underwent attempted radiofrequency ablation of the putative arrhythmic site. Three of six patients had evidence suggestive of a nodofascicular tract. Intermittent antegrade conduction over a left-sided nodofascicular tract was present in two patients and the diagnosis of a concealed nodofascicular was made in the third patient after ruling out other tachycardia mechanisms. Two patients had automatic junctional tachycardia, and one patient had atrioventricular nodal reentry with proximal common pathway block. Attempted ablation in the posterior and mid-septum was unsuccessful in patients with nodofascicular tachycardia. In contrast, those with atrioventricular nodal reentry and automatic junctional tachycardia readily responded to ablation. The presence of a nodofascicular tachycardia should be suspected if: (1) intermittent antegrade preexcitation is recorded, (2) the tachycardia can be initiated with a single atrial premature producing two ventricular complexes, and (3) a single ventricular extrastimulus initiates SVT without a retrograde His deflection. The presence of a nodofascicular pathway is common in patients with narrow complex tachycardia and VA block. Unlike AV nodal reentry and automatic junctional tachycardia, the response to ablation is poor.

Diagnostic approach to narrow complex tachycardia with VA block

Narrow complex tachycardia with VA block is rare. The differential diagnosis usually consists of (1) junctional tachycardia (JT) with retrograde block; (2) AV nodal reentrant tachycardia (AVNRT) with proximal common pathway block; and finally (3) nodofascicular tachycardia using the His-Purkinje system for antegrade conduction and a nodofascicular pathway for retrograde conduction. Analysis of tachycardia onset and termination, the effect of bundle branch block on tachycardia cycle length, and the response to atrial and ventricular premature depolarization must be carefully done. Making the correct diagnosis is crucial as the success rate in eliminating the tachycardia will depend on tachycardia mechanism.

Use of only a regular diagnostic His-bundle catheter for both fast and reproducible "para-Hisian pacing" and stable right ventricular pacing

INTRODUCTION

Para-Hisian pacing, i.e., pacing the anteroseptal right ventricle (RV) with or without direct capture of the His bundle (HB), allows the differentiation of VA conduction over the AV node from conduction over an accessory pathway. Classically, it is performed by maneuvering a separate pacing catheter around the HB catheter, which may be difficult and time-consuming.

METHODS AND RESULTS

This study prospectively evaluated the use of a single standard octapolar HB catheter with 2-mm interelectrode spacing for simultaneous (para-Hisian) pacing from the distal bipole and recording from the three proximal bipoles in 148 consecutive patients. Para-Hisian pacing was successful in 146 of 148 patients, performed within a median of only 10 seconds, and easily repeated several times during the course of an electrophysiologic study. Retrograde HB activation could be recorded in 132 of 146 patients; a clearly different surface ECG configuration confirmed the presence or absence of HB capture in all other patients. Interestingly, stable RV pacing could be performed from the HB catheter for the rest of the electrophysiologic study in 138 of 142 patients in whom this was tried. RV pacing from this site also led to better interpretation of retrograde conduction, due to clear visualization of retrograde HB activation.

CONCLUSION

Pacing from the distal bipole of a regular diagnostic HB catheter provides a fast and reliable way to perform para-Hisian pacing. Therefore, it may be advocated as a routine diagnostic protocol during electrophysiologic procedures. Moreover, pacing from this site obviates the need for a separate RV pacing catheter in most patients.

A left free-wall, decrementally conducting, atrioventricular (Mahaim) fiber: diagnosis at electrophysiological study and radiofrequency catheter ablation guided by direct recording of a Mahaim potential

A 64-year-old female with Wolff-Parkinson-White syndrome and an ECG demonstrating a right posterolateral accessory pathway was referred for electrophysiological study. During electrophysiological testing two AV pathways were identified: a right posterolateral pathway that displayed conventional electrophysiological properties: and a left free-wall pathway that conducted only anterogradely and demonstrated decremental properties. Two separate wide complex tachycardias were induced that utilized the left free-wall pathway anterogradely and either the AV node or the right posterolateral accessory pathway retrogradely. A discrete electrical potential on the free wall of the mitral annulus was identified during tachycardia and was utilized to facilitate mapping and ablation.

New observations on decremental atriofascicular and nodofascicular fibers: implications for catheter ablation

INTRODUCTION

The purpose of this study was to characterize the anatomy and physiology of accessory pathways that exhibit anterograde decremental conduction.

RESULTS

Among 100 consecutive patients with an accessory pathway undergoing electrophysiological study, six individuals with decremental anterograde accessory pathway conduction were identified. Anterograde accessory pathway effective refractory periods and conduction curves were assessed by atrial extrastimulus testing. Atrial pace mapping and ventricular activation sequence mapping were used to define accessory pathway origin and insertion. Surgical ablation (N = 1) or radiofrequency catheter ablation (N = 3) was performed based on accessory pathway anatomy as determined during electrophysiological study. Four of 6 patients had gaps in anterograde accessory pathway conduction. Two patients had evidence of functional longitudinal dissociation in the accessory pathway. Five of 6 patients had atriofascicular fibers with an atrial rather than AV nodal site of origin of their decrementally conducting accessory pathway and with distal insertions in the right bundle branch. Among these five patients, a right posterior atrial origin was nearly as common as a right anterior atrial origin. One patient had a true nodofascicular fiber that arose from the AV node, inserting distally into the left bundle branch.

CONCLUSION

Most accessory pathways with anterograde decremental conduction arise from the right anterior or right posterior atrium, not the AV node. A gap in anterograde accessory pathway conduction and functional longitudinal dissociation are common in such accessory pathways. Surgical or catheter ablation of such pathways is effective when directed at the atrial origin of the accessory pathway. True nodofascicular fibers arising from the AV node are rare. These may insert distally in the left ventricle. Catheter ablation of the proximal origin of such fibers is likely to result in complete AV block.

Characteristics of the ventricular insertion sites of accessory pathways with anterograde decremental conduction properties

BACKGROUND

Accessory pathways (APs) with anterograde decremental conduction properties referred to as Mahaim fibers have recently been recognized as originating from the right lateral atrium. Little information is available about their distal insertion. The purpose of this study was to determine the different kinds of APs involved and the characteristics of their distal insertion site.

METHODS AND RESULTS

Twenty-one patients (mean age, 28 +/- 13 years) with reciprocating tachycardia or atrial fibrillation were studied. Right-sided atrial and/or ventricular endocardial mapping during tachycardia identified different types of APs. (1) Seventeen patients had long APs originating from the right lateral atrium and coursing several centimeters to the right ventricle. In 10 patients, the AP terminated in or close to the right bundle-branch system (atriofascicular AP) and in 7, the AP terminated in the anterior right ventricle (atrioventricular AP). Patients with atriofascicular APs had narrower QRS complexes (133 +/- 10 versus 165 +/- 26 milliseconds, P = .02) and narrower initial r wave in leads V2 through V4 during maximal preexcitation than patients with atrioventricular APs. In addition, they had earlier His-bundle and right bundle-branch retrograde activation, ie, shorter V-His (16 +/- 5 versus 37 +/- 9 milliseconds, P < .01) and V-right bundle intervals (3 +/- 5 versus 25 +/- 6 milliseconds, P < .01). In 6 patients, minimal preexcitation not readily apparent was present in sinus rhythm despite the appearance of a narrow QRS complex. A wide distal insertion site of 0.5 to 2 cm in diameter consistent with arborization of the AP was found in 10 patients. The distal application of radiofrequency current produced a change in the preexcitation pattern in 4 patients and ablated the AP in 2 patients. In the other patients, radiofrequency current was applied more proximally and successfully ablated the AP bundle (n = 9) or AP proximal insertion (n = 6). No recurrence was observed during a follow-up period of 12 +/- 10 months. (2) Four patients had short paratricuspid atrioventricular APs; in one, the decremental conduction property was acquired as demonstrated by two electrophysiological studies performed 7 years apart. Radiofrequency ablation was successfully accomplished in all 4 patients at the tricuspid annulus.

CONCLUSIONS

Different types of APs account for tachycardias previously called Mahaim fibers. Long and short atrioventricular APs are observed in 81% and 19%, respectively. Long APs often have a distal arborization and may have either a fascicular or ventricular insertion. Radiofrequency current is more efficient when applied to the AP bundle or AP proximal insertion rather than to the distal insertion in patients with long APs.

Involvement of a nodofascicular connection in supraventricular tachycardia with VA dissociation

We present the case of a patient with episodes of supraventricular tachycardia and atrial dissociation that were terminated by either adenosine or verapamil. Involvement of an accessory pathway was shown by ventricular extrastimuli, elicited during His-bundle refractoriness, that interrupted the tachycardia or advanced the next His potential. The tachycardia circuit was demonstrated to be confined to the nodofascicular region based on the exclusion of surrounding tissues. Atrial activity, including that in the perinodal region, was totally dissociated during tachycardia. The lowest part of the circuit was determined to be located above the Hisian bifurcation, as multiple episodes with either a right or left bundle branch configuration during tachycardia did not modify the HH cycle. The ventricular septum summit was determined not to be involved, as no preexcitation was present during tachycardia or atrial pacing, and the right bundle branch was not part of the circuit. Radiofrequency current applied beneath the tricuspid valve at the His region successfully eliminated the nodofascicular connection with preservation of 1:1 AV conduction. The anatomical substrate underlying the abnormal connection may be either nodofasciculoventricular Mahaim fibers or a duality or dispersion of the nodo-Hisian conducting system.

Antidromic tachycardia utilizing decremental, latent accessory atrioventricular fibers: differentiation from adenosine-sensitive ventricular tachycardia

OBJECTIVES

We studied two patients with latent, decremental atrioventricular (AV) fibers in whom pre-excitation could be demonstrated only during wide complex tachycardia.

BACKGROUND

The presence of decremental AV fibers participating in antidromic AV reentrant tachycardia is usually suspected by the presence of pre-excitation either in sinus rhythm or during atrial pacing.

METHODS

Two patients were referred for evaluation and treatment of wide complex tachycardia whose configuration suggested ventricular tachycardia that could be terminated with adenosine infusion. They underwent standard electrophysiologic studies.

RESULTS

Baseline AH and HV intervals were normal. No pre-excitation was noted with atrial overdrive at multiple sites or during atrial extrastimulation. Retrograde conduction was present with a sequence compatible with AV node conduction. Sustained wide complex tachycardia was induced with ventricular overdrive pacing. Late atrial premature depolarizations during tachycardia pre-excited the subsequent ventricular activation. Earlier atrial premature depolarizations delayed the subsequent ventricular activation. In one patient, early atrial premature depolarizations terminated the tachycardia without activating the ventricle. In the other patient, spontaneous tachycardia termination was accompanied by ventriculoatrial block. The earliest ventricular activation was at the annulus in the posteroseptal region in one patient and at the left posterior region in the other. Atrioventricular node reentry and atrial tachycardia with bystander AV fibers were also excluded. These findings establish the diagnosis of antidromic AV reentrant tachycardia utilizing a slow, decrementally conducting AV pathway.

CONCLUSIONS

This is the first report describing the presence of latent, decremental accessory AV pathways in which conduction was manifest only during antidromic AV reentrant tachycardia. To differentiate these wide complex tachycardias from adenosine-sensitive ventricular tachycardia, we recommend that atrial premature depolarizations be applied during tachycardia to rule out the presence of a latent, decremental AV fiber even in patients who do not otherwise have pre-excitation with atrial pacing techniques.

Catheter-induced mechanical conduction block of right-sided accessory fibers with Mahaim-type preexcitation to guide radiofrequency ablation

BACKGROUND

Accessory pathways originating at the tricuspid annulus that exhibit decremental antegrade conduction properties (Mahaim-type preexcitation) are amenable to radiofrequency (RF) current catheter ablation. However, a reliable and reproducible strategy for mapping and ablation of these fibers is lacking.

METHODS AND RESULTS

Eleven patients with preexcited atrioventricular tachycardia involving a decrementally conducting antegrade accessory pathway underwent complete electrophysiological evaluation and subsequent attempts at RF catheter ablation. Mechanical conduction block at the subannular level of the atrial input to the accessory fiber was induced by catheter manipulation in 8 patients, in 2 of them during atrial fibrillation. RF current was delivered, after resumption of preexcitation, to the site of mechanical block during atrial pacing (n = 6) or atrial fibrillation (n = 2) and eliminated the accessory pathway in all 8 patients. In another patient, mechanical block was not observed, but ablation of the atrial accessory fiber insertion was achieved at the subannular level during atrioventricular tachycardia. The anatomic site of ablation along the tricuspid annulus was anterolateral (n = 1), lateral (n = 3), or posterolateral (n = 5). Failures were encountered in the first patient of the series in whom ablation attempts were directed at the ventricular insertion of the accessory fiber and in a patient in whom ablation of the atrial insertion was attempted at the supraannular level. Recurrence of preexcitation within 12 hours was observed in 5 of 6 patients in whom ablation had been achieved during atrial pacing. Eventually successful repeat sessions were performed the following day using a simplified ablation approach. Thus, a median of 5 RF pulses (range, 1 to 26) per accessory fiber eliminated conduction in 9 (82%) of the 11 patients in 1.9 +/- 0.9 sessions. During a follow-up of 9.5 +/- 2.3 months, preexcitation recurred in 1 patient.

CONCLUSIONS

The atrial origin of accessory connections with Mahaim-type preexcitation is apparently confined to the anterolateral-to-posterolateral region of the tricuspid annulus. Mechanical conduction block in the atrial input to the accessory fiber induced at the subannular level by catheter manipulation provides an optimal marker to locate the ablation site, even during atrial fibrillation. To expose early recurrence of antegrade accessory pathway conduction, intermittent atrial pacing in the 12 hours after ablation is advisable; in cases of recurrence, a repeat procedure can readily be performed using just the ablation catheter advanced to the target site at the tricuspid annulus.

Catheter ablation of Mahaim fibers with preservation of atrioventricular nodal conduction

Three patients with refractory preexcited tachycardia implicating Mahaim fibers underwent attempted catheter ablation of the accessory pathway. In the absence of demonstrable retrograde conduction in Mahaim fibers, we located the accessory pathway ventricular insertion site using the criteria of concordance between paced and spontaneous QRS morphologies during pace-mapping and earliest onset of local electrogram relative to surface preexcited QRS. At this site, a QS-like pattern of unfiltered unipolar electrograms with steep downstroke was recorded. The optimal site appeared radiologically at the right ventricular anterior wall or the adjacent septum, 2-4 cm from the tricuspid anulus. Three to six 160-J shocks were delivered at this site using an anterior chest wall plate as anode. After fulguration, conduction through the Mahaim tract was absent. A right bundle branch block persisted in two patients. All patients remained free of preexcited tachycardia during 12-16 months of follow-up. Postablation electrophysiological assessment showed no preexcitation in any patient. No reciprocating tachycardia was inducible, even during isoproterenol infusion. Atrioventricular nodal conduction parameters were unchanged from baseline study. Catheter ablation of Mahaim fibers is an effective alternative method for the treatment of tachycardias that include the accessory pathway in the circuit.

The scintigraphic characteristics of ventricular pre-excitation through Mahaim fibers with the use of phase analysis

The phase image pattern of blood pool scintigrams was blindly assessed in 11 patients exhibiting conduction through Mahaim pathways, including 6 nodoventricular and 5 fasciculoventricular. These patterns were compared with the phase image findings in normal subjects, patients with left and right bundle branch block in the absence of pre-excitation and patients with pre-excitation through atrioventricular (AV) connections. In all patients with a Mahaim pathway, the site of earliest phase angle was septal or paraseptal. Phase progression was asymmetric and the pre-excited ventricle demonstrated the earliest mean ventricular phase angle in 10 of 11 patients. This pattern, and the associated ventricular phase difference, appeared to vary from that in normal subjects and in those with a septal AV connection, in whom phase progression is generally symmetric. Scintigraphic phase analysis provided localizing information and presented patterns consistent with Mahaim pathways. Although not able to differentiate among Mahaim pathway subtypes, these phase patterns differed from those in normal subjects, those with right and left lateral free wall pathways and most patients with a septal AV pathway. However, the phase pattern of patients with a Mahaim pathway may not differ from that of patients with a septal AV connection displaying an asymmetric pattern of phase progression, or those with left and right bundle branch block in the absence of pre-excitation. Objective, yet imperfect phase measurements supported these differences. Such image findings may complement the often complex electrophysiologic evaluation of patients presenting with pre-excitation.