[Wide spectrum of arrhythmias, with inductions and terminations of atrio-ventricular replica-nodal tachycardia by automaticity during successful radiofrequency ablation of long anterogradely slow conducting atrio-fasciculo-ventricular accessory pathway]

Mahaim syndrome is still a challenge. The specific characteristics of the pathway, the fact that it seldom occurs, and ambiguities about the pathophysiology and nomenclature make it, for electrophysiologists, still difficult to ablate. We present a case of a patient with anterogradely slow conducting accessory pathway, which has been effectively ablated although M potential was not observed nor was a mechanical conducting block of the accessory pathway. The accessory pathway showed a wide spectrum of electrophysiological characteristics of the "AV node physiology" including inductions and terminations of atrio-ventricular replica-nodal tachycardia by local automaticity, not only during electrophysiological study, but during successful application. The accessory pathway presented signs of two types of pseudo Mahaim fibers: atrio-fascicular and slow conducting atrio-ventricular connection.

The clinical course and risk in patients with pseudo-Mahaim fibers

BACKGROUND

Pseudo-Mahaim (AP-M) fibers are a rare variant of atrioventricular (AV) accessory pathways. Atriofascicular and atrioventricular accessory connections are characterized by slow conduction and decremental properties. Dual physiological AV node pathways, slow and fast, are observed in a large number of patients with AP-M. Therefore, there is substrate for AV nodal reentrant tachycardia (AVNRT) in addition to antidromic AV reentrant tachycardia (AVRT) with left bundle branch block (LBBB)-like morphology. Other arrhythmia such as atrial fibrillation (AF) or atrial flutter (AFL) and ventricular fibrillation (VF) are also observed. We analysed the occurrence of arrhythmias in a group of patients with AP-M treated in our department.

METHODS

We evaluated 27 patients (12 women) aged 14-53 years (mean age 25.6 years) with AP-M. The clinical course in these patients, in particular with regard to the occurrence of arrhythmias, was analysed. Patients with dual AV node properties were compared to patients without such findings.

RESULTS

We found dual AV node properties in 18 patients (Group 1), while 9 patients had fast pathway only (Group 2). Twenty-six patients presented with AVRT, 2 patients with AVNRT, 3 patients with AF, 1 patient with AT, 2 patients with AFL, and 3 patients with VF. In 2 patients, AP-M were seen in an atypical area. In one patient, the pathway connected the right atrium with the left ventricle (septal region), and in the other patient it connected the left atrium with the left ventricle (left anterior region).

CONCLUSIONS

The majority of AP-M was right-sided. Two thirds of patients with AP-M had anatomical substrate for AVNRT (fast/slow pathway AV node). VF or asystole occurred in 10% of patients.

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.

Entrainment Mapping of a Concealed Nodoventricular Accessory Pathway in a Man with Complete Heart Block and Tachycardia-Induced Cardiomyopathy

True nodoventricular (NV) accessory connections, as originally described by Mahaim, are rare entities, with the majority of previously reported cases now recognized as being due to decremental atriofascicular pathways. Here, we present a patient with incessant narrow and wide QRS complex tachycardia occurring in the setting of prior complete heart block. Entrainment mapping proved useful in diagnosing orthodromic reentry utilizing a concealed right septal NV pathway. The patient was successfully treated with radiofrequency ablation, resulting in a marked improvement in left ventricular function.

The 12-lead ECG in patients with Mahaim fibers

The aim of this review article is to discuss the electrocardiographic presentation of the so called variants of pre-excitation ("Mahaim fibers") during sinus rhythm and tachycardia.

Cryoablation of a Nodoventricular Mahaim Fiber

An 11-year old female presented with paroxysmal tachycardia and was diagnosed with a Mahaim fiber during electrophysiologic study. A preexcited tachycardia and the typical variety of AV nodal reentry tachycardia were induced at different times. During preexcited tachycardia, the His bundle electrogram followed the ventricular electrogram, and, introduction of atrial premature beats at different coupling intervals, advanced the peri-AV nodal atrial tissue, with no change in the ventricular cycle length, leading to a diagnosis of an antidromic tachycardia due to a nodoventricular fiber. Cryoablation at a mid-septal location under three-dimensional guidance successfully eliminated both tachycardias without detrimental effects to the AV node.

Electrocardiogram during tachycardia in patients with anterograde conduction over a Mahaim fiber: old criteria revisited

OBJECTIVES

The aim of this study was to prospectively evaluate the sensitivity, specificity, and positive and negative predictive values of previously described ECG criteria to identify preexcited tachycardia due to decrementally conducting accessory pathways (QRS axis between 0 and -75 degrees , QRS width < or = 0.15 seconds, an R wave in lead I, an rS pattern in lead V(1), RS > 1 QRS transition > V(4), and cycle length between 220 and 450 ms).

BACKGROUND

Preexcited tachycardia associated with decrementally conducting right-sided accessory pathways usually shows a rather "narrow" QRS complex and can be difficult to differentiate from supraventricular tachycardia (SVT) with left bundle branch block (LBBB) aberrant conduction.

METHODS

We analyzed three groups of patients: 32 patients with an atriofascicular pathway (group I); 8 patients with long (n = 3) or short (n = 5) decrementally conducting right-sided AV pathway (group II); and a control group that consisted of 35 patients with SVT and LBBB (group III).

RESULTS

Presence of all six criteria had 87.5% sensitivity in group I and a 0% sensitivity in group II. There were four false negatives in group I. The negative predictive value was 82.5%, with six false positives in group III (five patients with an aberrant LBBB-shaped tachycardia with ventriculoatrial conduction over an accessory AV pathway). The criterion cycle length was not helpful.

CONCLUSIONS

Criteria for identifying a tachycardia with anterograde conduction over a Mahaim fiber are helpful only in atriofascicular pathways, with a sensitivity of 87.5% and a negative predictive value of 82.5%. The major cause of false positives was a tachycardia with aberrant LBBB conduction and ventriculoatrial conduction over an accessory AV pathway.

The electrocardiogram during sinus rhythm and tachycardia in patients with Mahaim fibers: the importance of an "rS" pattern in lead III

OBJECTIVES

The purpose of the study was to identify the electrocardiographic (ECG) characteristics of the Mahaim fiber.

BACKGROUND

Mahaim fibers are slowly conducting accessory pathways reaching into the right ventricle. They often play a role in tachycardias.

METHODS

We retrospectively analyzed 40 patients with Mahaim fibers. Five patients had associated Wolff-Parkinson-White syndrome and were excluded from the study. Two patients had a short atrioventricular decremental accessory pathway and were also excluded. The remaining 33 patients had a tachycardia with anterograde conduction over a Mahaim fiber. Twenty were female. Their mean age was 24 +/- 10 years.

RESULTS

The most common pattern of minimal preexcitation during sinus rhythm was an rS pattern in lead III. This was found in 20 patients. There was a match between the presence of rS in lead III during sinus rhythm and left axis deviation during tachycardia with anterograde conduction over the Mahaim fiber. After ablation, a different QRS pattern emerged in lead III, indicating the absence of conduction over the Mahaim fiber. To obtain information on the prevalence of an rS pattern in lead III in age-matched controls with palpitations and without structural heart disease, the 12-lead ECG of 200 young individuals were examined. An rS pattern in lead III was found in 6%.

CONCLUSIONS

A narrow QRS with an rS pattern in lead III during sinus rhythm in a patient with a history of palpitations should alert the physician to the possibility of a Mahaim fiber. During tachycardia, these patients typically show a left bundle branch block-like QRS complex with left axis deviation.

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.

Latent Mahaim fiber as a cause of antidromic reciprocating tachycardia: recognition and successful radiofrequency ablation

The term "Mahaim fiber" usually is applied to an atriofascicular fiber that inserts distally into the right bundle branch and forms the anterograde limb of a reciprocating tachycardia. One of the features that has been used to describe the physiology of Mahaim fibers is the presence of anterograde preexcitation. We describe two patients who had a clinical tachycardia consistent with a "Mahaim tachycardia" in whom there was no evidence or minimal evidence of anterograde preexcitation during sinus rhythm or atrial pacing. In both patients, the tachycardia was rendered noninducible by radiofrequency ablation at the site of Mahaim potentials at the tricuspid annulus, and a long-term cure was achieved. This is the first description of a "latent Mahaim fiber" that does not cause preexcitation but which can support antidromic reciprocating tachycardia.

Orthodromic tachycardia with atrioventricular dissociation: evidence for a nodoventricular (Mahaim) fiber

We describe a patient in whom two tachycardias with AV dissociation were inducible by ventricular extrastimulation. The first tachycardia was characterized by a narrow QRS preceded by a His deflection with an HV interval identical to that recorded in sinus rhythm (40 ms). Premature ventricular depolarization delivered when the His bundle was refractory advanced the next His deflection. These findings suggest the presence of a nodoventricular bypass tract involved in an orthodromic tachycardia. The second tachycardia was induced after propafenone infusion and exhibited a wide QRS complex with left bundle branch block morphology; each ventricular complex was consistently associated with a His deflection with a HV interval of -15 ms. The second tachycardia may be considered to represent an antidromic tachycardia through the nodoventricular tract. However, a ventricular tachycardia cannot be excluded.

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.

Mahaim tachycardias

Patients with Mahaim fibres form a distinct subgroup of the pre-excitation syndromes (less than 3%). They have episodes of a pre-excitation during sinus rhythm. Originally, Mahaim fibres have been classified into two main groups, nodoventricular and fasciculoventricular fibres. Recent evidence from both surgery and catheter ablation has shown that the substrate for tachycardia arises due to a slowly conducting fright atrioventricular (AV) accessory pathway (AP) with decremental properties. The pre-excited tachycardia (antidromic re-entrant tachycardia) is distinctive with a left bundle branch block (LBBB) pattern, long AV interval (due to the long conduction time over the AP) and short VA interval (over the AV node). The majority of these patients do not have episodes of narrow QRS complex, due to the absence of retrograde conduction of the AP. There are several ECG features that suggest Mahaim tachycardia as a cause of LBBB pattern tachycardia: QRS axis superior or between 0 degrees and 75 degrees, QRS duration of 0.15 s or less and precordial transition in lead V4 or after. Clinically, Ebstein's anomaly is relatively common and multiple APs are also observed with an increased frequency. Small studies and cases reports have demonstrated sensitivity to various classes of AA drugs. Class IA, IC and beta-blocker may be effective in preventing tachycardias. Small surgical series have reported excellent results in patients with accessory AV connections and Mahaim fibres tachycardia. However catheter ablation offers a definitive therapy in such patients with a high success rate and minimal morbidity.

[Accessory atrioventricular pathways with decremental conduction (Mahaim connections). 2 case reports]

The so called Mahaim connections form a relatively scarce variant of the preexcitation syndrome. Antidromic atrioventricular reentry tachycardia with wide QRS complex of LBBB morphology represents a typical clinical manifestation of the condition. Nodofascicular and nodoventricular fibres in all the probability do exist, but only rarely. Most of these accessory pathways are located on the firht free wall and conduct only antegradely and decrementally. Majority of these pathways are formed by long bundles inserting in the terminal part of the right bundle branch or in the myocardium near the right ventricular apex. In this setting traditional mapping strategy is of little use and different approaches must be employed. Only minority of these right-sided accessory pathways are short inserting in the ventricular myocardium under the tricuspid annulus. We present two case reports of patients with accessory connections exhibiting the so called Mahaim electrophysiology. In the first case, the pathway was merely an innocent bystander that, however, masked serious low intrahissian conduction disturbance. In the second case, the patient had a long-standing characteristic symptomatology due to the right anterolateral short accessory pathway which was successfully mapped and ablated.

Preexcitation in hypertrophic cardiomyopathy: a case of a fasciculoventricular Mahaim fiber

A patient with hypertrophic cardiomyopathy (HCM) who presented with preexcitation pattern on the surface ECG suggestive of the Wolff-Parkinson-White (WPW) syndrome is described. Intracardiac electrophysiological study revealed a fixed anomalous QRS complex and a short-fixed His-ventricular interval indicating a fasciculoventricular Mahaim fiber. As this specific form of accessory connection does not cause reentrant tachycardias, no treatment was required. It is important to distinguish this entity from atriofascicular or nodoventricular Mahaim fibers or the WPW syndrome in patients with HCM showing a preexcitation pattern in the surface ECG, as these may cause life-threatening arrhythmias in this patient population.

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.

Hypothesis testing as an approach to the analysis of complex tachycardias--an illustrative case of a preexcitation variant

The correct elucidation of the electrophysiological substrate and mechanism(s) responsible for a complex arrhythmia requires a systematic approach to the analysis of the electrophysiological data. One approach calls for the formulation of a set of hypotheses that could explain the data obtained during the study. The hypotheses are then tested for compatibility with phenomena observed and the one that agrees with the majority of the findings would represent the most tenable explanation. We present the case of a young girl with a wide QRS complex tachycardia and a history of ventricular preexcitation that illustrates this approach. The complexities were resolved only after intraoperative analysis and surgical ablation of a right-sided accessory pathway with decremental properties, and provides further insight into our understanding of the nodoventricular Mahaim fiber.

AV nodal reentrant tachycardia with Mahaim fiber conduction

Paroxysmal tachycardia with widened QRS complexes was found in a 46-year-old woman. In sinus rhythm, the patient had electrocardiographic evidence of type B preexcitation with a left bundle branch block pattern. The resting PR interval (160 msec) and A-H interval (100 msec) were within normal limits, but the H-V interval (10 msec) was abnormally short. Programmed atrial extrastimuli at progressively shorter coupling intervals resulted in sudden prolongation of the A-H interval from 120 msec to 250 msec, and the His bundle activities became incorporated just after initiation of the QRS complexes. The QRS morphology was changed but the change was minimal, and atrial echo beats or sustained tachycardia with wide and preexcited QRS complexes were elicited. It is postulated that the site of reentry is within the AV node with preexcitation occurring as the result of conduction in an anomalous nodoventricular pathway.

Atriofascicular connection or a nodoventricular Mahaim fiber? Electrophysiologic elucidation of the pathway and associated reentrant circuit

Accessory pathways showing decremental properties and inserting into the right ventricle have been frequently described as "nodoventricular" or Mahaim pathways. However, conclusive evidence for a nodal origination of such pathways is lacking. The patient in this study had characteristics typical of such a pathway. Antegradely, the pathway showed decremental, nodelike conduction properties. With the aid of right bundle branch recordings, the pathway was demonstrated to insert directly into the right bundle branch. Atrioventricular reciprocating tachycardia could be readily initiated by atrial or ventricular pacing. The QRS morphology was normal during sinus rhythm and demonstrated a left bundle branch block pattern with normal axis during tachycardia. The reentrant circuit involved antegrade conduction over the accessory pathway and retrograde conduction via the bundle branches, His bundle, and the atrioventricular node. More significantly, late atrial stimuli delivered during tachycardia could preexcite the ventricle via the accessory pathway despite their inability to enter the atrioventricular node. Thus, the upper "turn around" of the reentrant circuit involved atrial tissue and the accessory pathway originated directly from the right atrium independent of the atrioventricular node. In view of these new findings and other recent observations during surgical resection of similar pathways, a reassessment of previous descriptions of "nodoventricular" fibers may be necessary. Many of these pathways may actually represent atriofascicular or atrioventricular connections with decremental properties.

Successive myocardial infarctions in a patient with Mahaim fiber syndrome

A patient with Mahaim fiber syndrome suffered two acute myocardial infarctions during the last two years. Anomalous atrioventricular excitation was intermittent. Diagnosis of both anteroseptal and anterolateral electrocardiographic myocardial infarction could be made despite ventricular pre-excitation. These findings have not been previously published, to our knowledge.