Short atrioventricular Mahaim fibers: observations on their clinical, electrocardiographic, and electrophysiologic profile

Short A-V manheim fiber. INTRODUCTION: A short atrioventricular decrementally conducting accessory pathway is an uncommon variant of preexcitation. Available data from small series suggest that their decremental properties might not be caused by A-V nodal-like tissue. METHODS: We compared clinical, electrocardiographic and electrophysiologic parameters in two groups of patients: 8 patients with a short A-V Mahaim pathway (Group A), and 33 patients with atriofascicular pathways (Group B). Radiofrequency catheter ablation was carried out guided by activation mapping at the annulus in Group A patients and targeting the "M" potential in Group B patients. RESULTS: After ablation of all associated rapidly conducting bypass tracts, 7 of the 8 Group A patients showed clear preexcitation. In only 1 of 8 patients the short A-V Mahaim fiber was actively engaged in a reentrant tachycardia circuit. During radiofrequency catheter ablation an automatic rhythm occurred in 4 of 8 patients. Intravenous adenosine caused conduction a block in the Mahaim fiber in 3 of the 5 patients tested. In group B, no patient showed clear preexcitation (P<00001) while 72% had a minimal preexcitation pattern. Twenty-nine of the 33 patients had a circus movement tachycardia with AV conduction over the atriofascicular fiber. During radiofrequency catheter ablation 30 of 33 patients showed accessory pathway automaticity. Adenosine caused transient block at the atriofascicular pathway in 11 (92%) of the 12 patients tested. CONCLUSIONS: While short decrementally conducting right-sided accessory pathways show a typical ECG pattern different from atriofascicular pathways, their electrophysiologic properties do not seem to be uniform. Those pathways can be successfully interrupted by catheter ablation.     

Catheter Ablation of the Atrial Origin of a Decrementally Conducting Atriofascicular Accessory Pathway by Radiofrequency Current

Radiofrequency Ablation of Pseudo-Mahaim Fibers. Introduction: A young woman with refractory recurrent supraventricular tachycardia was referred for catheter ablation. Methods and Results: Electrophysiologic studies revealed the mechanism of tachycardia to be atrioventricular (AV) reentry, utilizing a decrementally conducting atriofascicular accessory pathway as the anterograde limb of the circuit and the normal intraventricular conducting system as the retrograde limb. Pace mapping in the right atrium during sinus rhythm suggested an atrial origin of the accessory pathway several centimeters distant from the AV node. Multiple radiofrequency lesions at the distal insertion of the accessory pathway in or near the right bundle branch failed to abolish preexcitation. In contrast, radiofrequency current applied to the ventricular side of the anterolateral tricuspid ring, adjacent to the atrial origin of the accessory pathway, was successful in abolishing preexcitation and inducible supraventricular tachycardia without affecting AV nodal conduction. Conclusion: Radiofrequency ablation can provide curative therapy for intractable supraventricular tachycardia due to decrementally-conducting atriofascicular accessory pathways. The risk of AV block in such patients as a consequence of the procedure should be quite low.     

Effects of right bundle branch block on the antidromic circus movement tachycardia in patients with presumed atriofascicular pathways

BACKGROUND: The typical and most common tachycardia in patients with atriofascicular pathways is a macro reentrant tachycardia, with anterograde conduction over the decrementally conducting bypass tract and retrograde conduction over the right bundle branch-His-AV node axis resulting in a short V-right bundle branch and short V-H interval. OBJECTIVES: To report on changes in rate and QRS configuration when right bundle branch block (RBBB) develops spontaneously during antidromic tachycardia using an atriofascicular fiber. METHODS: Three of 25 patients with an antidromic circus movement tachycardia using a right-sided atriofascicular pathway showed episodes of right bundle branch block (RBBB) during ventriculo-atrial conduction. Effect of retrograde RBBB on tachycardia rate and QRS configuration was studied using intracardiac and extracardiac recordings. RESULTS: All 3 patients showed prolongation of their V-A interval when retrograde RBBB occurred during tachycardia, resulting in a longer tachycardia cycle length. The VA time increase ranged from 85 to 100 msec, with a mean 346 +/- 5 msec. Two of the 3 patients also showed a change in QRS configuration due to a more leftward shift of the frontal plane QRS axis. CONCLUSION: Rate changes in antidromic tachycardia in patients with atriofascicular fibers can be based on a shift in VA conduction from one bundle branch to the other. This may be accompanied by changes in the frontal plane QRS axis because of a change in ventricular activation sequence.     

Mahaim fiber: An atriofascicular or a long atrioventricular pathway?

There is debate concerning the distal insertion of Mahaim fibers. Some findings favor an atriofascicular fiber connected with the distal right bundle branch. Other findings favor a long atrioventricular (AV) structure inserting into the myocardium. A patient having a decrementally conducting accessory pathway is reported. Proximal and distal Mahaim potentials were recorded during sinus rhythm, atrial pacing, and antidromic tachycardia. Both proximal and distal M potentials always preceded the QRS complex during sinus rhythm and antidromic tachycardia earlier than the right bundle branch potential. During tachycardia, the distal M potential was recorded 6 ms before the retrograde right bundle potential. Other arguments consistent with an AV connection were a change in the QRS configuration during tachycardia after the first radiofrequency pulse at the site of the distal M potential and absence of right bundle branch block after successful ablation. Conduction through the proximal part of the Mahaim fiber was unaltered after ablation, as assessed by recording the proximal M potential. Electrophysiologic evidence is presented suggesting a long AV accessory pathway inserting close to the distal right bundle branch rather than an atriofascicular connection in this patient with a Mahaim fiber.     

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.     

Case Report: Spontaneous Atriofascicular Pathway Automaticity Simulating Ventricular Tachycardia

Atriofascicular pathways most commonly present electrocardiographically as an antidromic reciprocating AV reentrant tachycardia. We report the case of a child who presented in infancy with a wide QRS complex tachycardia thought to be supraventricular tachycardia with aberrant conduction, associated with tachycardia-induced cardiomyopathy. Later in life the same patient represented with episodes of palpitations secondary to a wide QRS complex tachycardia, thought to be ventricular tachycardia. Electrophysiologic mapping demonstrated the origin of the wide QRS complex tachycardia was from automatic activity originating from a right anterolateral atriofascicular pathway, which also participated in a reentrant antidromic AV reciprocating tachycardia. Radiofrequency ablation of the atriofascicular pathway successfully eliminated both arrhythmias. The mechanism of the wide QRS complex tachycardia appeared to result from spontaneous automaticity of the atriofascicular pathway.     

Initiation of atrioventricular nodal reentrant tachycardia in patients with discontinuous anterograde atrioventricular nodal conduction curves with and without documented supraventricular tachycardia: Observations on the role of a discontinuous retrograde conduction curve

To evaluate factors playing a role in initiation of atrioventricular (AV) nodal reentrant tachycardia utilizing anterogradely a slow and retrogradely a fast conducting AV nodal pathway, 38 patients having no accessory pathways and showing discontinuous anterograde AV nodal conduction curves during atrial stimulation were studied. Twenty-two patients (group A) underwent an electrophysiologic investigation because of recurrent paroxysmal supraventricular tachycardia (SVT) that had been electrocardiographically documented before the study. Sixteen patients (group B) underwent the study because of a history of palpitations (15 patients) or recurrent ventricular tachycardia (one patient); in none of them had SVT ever been electrocardiographically documented before the investigation. Twenty-one of the 22 patients of group A demonstrated continuous retrograde conduction curves during ventricular stimulation. In 20 tachycardia was initiated by either a single atrial premature beat (18 patients) or by two atrial premature beats. Fifteen of the 16 patients of group B had discontinuous retrograde conduction curves during ventricular stimulation, with a long refractory period of their retrograde fast pathway. Tachycardia was initiated by multiple atrial premature beats in one patient. Thirteen out of the remaining 15 patients received atropine. Thereafter tachycardia could be initiated in three patients by a single atrial premature beat, by two atrial premature beats in one patient, and by incremental atrial pacing in another patient. In the remaining eight patients tachycardia could not be initiated. Our observations indicate that the pattern of ventriculoatrial conduction found during ventricular stimulation is a marker for ease of initiation of AV nodal tachycardia in patients with discontinuous anterograde AV nodal conduction curves.     

Demonstration of Retrograde Conduction over an Atriofascicular Accessory Pathway

Atriofascicular Pathway with Retrograde Conduction. Introduction : Absence of retrograde conduction over a right atriofascicular accessory pathway causing reciprocating tachycardia has been considered a hallmark of this clinical entity.
Methods and Results : This report describes successful catheter ablation in a patient presenting with the distinctive pattern of preexcited left bundle branch block tachycardia utilizing a right atriofascicular accessory pathway. This pathway, however, exhibited the unique capability of ventriculoatrial conduction. Both anterograde and retrograde conduction were characterized by "node-like" properties.
Conclusion : Demonstration of retrograde accessory pathway conduction in this particular setting does not exclude the diagnosis of a single, atriofascicular accessory pathway.     

Differenzialdiagnostik und Therapie tachykarder Herzrhythmusstörungen

The 12-channel surface electrocardiogram (ECG) is an important diagnostic tool for diagnosis of arrhythmias and acute coronary syndrome. Supraventricular tachycardia (SVT) is a paroxysmal tachycardia as are sinus tachycardia, atrial tachycardia, atrioventricular (AV) nodal reentry tachycardia and tachycardia due to accessory pathways. All SVTs are characterized by a ventricular heart rate >?100 beats/min and small QRS complexes (QRS width <?0.12 s) during tachycardia. It is important to analyze the relation between p-wave and QRS complex, to look for an electric alternans as a main finding for an accessory pathway. Wide QRS complex tachycardia (QRS width ≥?0.12 s) occurs in SVT with aberrant conduction, SVT with bundle branch block or ventricular tachycardia (VT). In broad complex tachycardia, AV dissociation, negative or positive concordant patterns in V1–V6, a notch in V1 and qR complexes in V6 in tachycardia with left bundle branch block morphology, are findings indicating VT. In addition, an R/S relation <?1 in V6 favors VT when right bundle branch block tachycardia morphologies are present. By analyzing the surface ECG in the correct way with a systematic approach, the specificity and sensitivity of correctly identifying SVT or VT can be raised to >?95?%. Therapy of tachycardia is possible with few antiarrhythmic drugs (concept of the 5As), beta-blocking agents, cardioversion and defibrillation. Using these approaches termination of tachycardia is possible in the majority of cases with high success rates.     

A new method for estimating preexcitation index without extrastimulus technique and its usefulness in determining the mechanism of supraventricular tachycardia.

The preexcitation index has been shown to be useful in determining the mechanism of paroxysmal supraventricular tachycardia (SVT) and the site of the accessory pathway in atrioventricular (AV) reentrant tachycardia. To test whether a preexcitation index could be computed analytically instead of by scanning the whole SVT cycle with extrastimuli, 19 patients with SVT were studied. The new index was computed using the following formula: (AV conduction time during SVT) + (ventriculoatrial conduction time during ventricular pacing at the SVT cycle length) - (SVT cycle length). There was a strong correlation between the preexcitation index determined by the extrastimulus technique and the new index in 15 patients in whom the preexcitation index could be determined (r = 0.99, p less than 0.01). The value on the new index was greater than 90 ms only in patients with dual AV nodal pathways. In the 4 patients in whom the preexcitation index could not be determined by the extrastimulus technique, the new index could differentiate AV reentrant tachycardia (index for 2 patients, 60 and 60 ms, respectively) from AV nodal reentrant tachycardia (index for 2 patients, 100 and 105 ms, respectively). In conclusion, the new index provided help in determining the mechanism of SVT, even when retrograde atrial preexcitation by a ventricular extrastimulus did not occur.     

12-Kanal-Elektrokardiogramm

The surface electrocardiogram (ECG) is an important diagnostic tool for the diagnosis of arrhythmias and acute coronary syndrome. Supraventricular tachycardias (SVT) are paroxysmal tachycardias as are sinus tachycardia, atrial tachycardia, AV nodal reentry tachycardia, and tachycardia due to accessory pathways. All SVT are characterized by a ventricular heart rate >100/min and small QRS complexes (QRS width <0.12 s) during tachycardia. It is important to analyze the relation between P wave and QRS complex to look for an electrical alternans as a leading finding for an accessory pathway. Wide QRS complex tachycardias (QRS width ≥ 0.12 s) occur in SVT with aberrant conduction and SVT with bundle branch block or ventricular tachycardia (VT). In broad complex tachycardias, AV dissociation, negative or positive concordant pattern in V₁–V₆, a notch in V₁ and QR complexes in V₆ in tachycardias with left bundle branch block morphologies are findings indicating VT. In addition, an R/S relation <1 in V₆ favors VT when right bundle branch block tachycardia morphologies are present. By analyzing the surface ECG in the right way with a systematic approach, the specificity and sensitivity of correctly identifying a SVT or VT can be raised by >95%. The 12-lead surface ECG allows the coronary culprit lesion to be located in 97% due to determination of the 12-lead ST segment deviation score.     

12-Kanal-Elektrokardiogramm bei Kindern und Jugendlichen

The surface electrocardiogram (ECG) is an important diagnostic tool in general medicine, for children, adolescents and adults. Although technical aspects of ECG recordings are similar in young and old patients, there are some age-specific differences between children and adults. The QRS axis shifts from right to left at several stages during childhood. The heart rate decreases from 140/min (newborns) to 130/min (young children) to 75/min (adolescents). First and second degree atrioventricular (AV) blocks (I and II type Wenckebach) are frequent in children. Duration of the QRS is age-dependent as is the R peak amplitude. The ST-segment elevation is relatively frequent in children and is normal up to 0.1 mV. Negative T waves diminish with age and QTc times are also age-dependent. Supraventricular tachycardia (SVT) is characterized by small QRS complexes (QRS width <?0.12 s) during tachycardia. It is important to analyze the relationship between the p wave and QRS complex and to look for electrical alternans as a leading finding for an accessory pathway. Wide QRS complex tachycardia (QRS width ≥?0.12 s) occurs in SVT with aberrant conduction, SVT with bundle branch block or ventricular tachycardia (VT). In broad complex tachycardia, AV dissociation, negative or positive concordant pattern in V₁–V₆, a notch in V₁ and qR complexes in V₆ in tachycardia with left bundle branch block morphologies are findings indicating VT. In addition, an R/S relationship in V₆ favors VT when right bundle branch block tachycardia morphologies are present. By analyzing the surface ECG in the correct way with a systematic approach, a specificity and sensitivity of correctly identifying SVT or VT of over 95?% can be achieved.     

Injectable and oral propafenone in nodal reentry and pathways of ventricular preexcitation

Propafenone, an antiarrhythmic drug of IC type, was applied to 10 patients with supraventricular tachycardia (SVT) produced by intranodal reentry (group I) and in 14 patients with reentry by an accessory atrioventricular (AV) pathway (group II), 10 of them suffering from orthodromic SVT. Propafenone given intravenously depresses or blocks the antegrade or retrograde conduction in the AV node and in the accessory AV pathway. The same effect is observed with orally given propafenone: 66% of antegrade blocking and 54% of retrograde blocking of the accessory conduction pathway. Intravenously given propafenone reduces within 2 to 3 min by antegrade or retrograde blocking 70% of SVT produced by intranodal reentry and by 85% of SVT produced by reentry by the accessory pathway. After injection it becomes impossible to induce intranodal SVT in 60% of cases and SVT by the accessory pathway reentry in 28% of cases. With oral treatment (600 mg/day) reinduction of intranodal SVT becomes impossible in 66% of cases and of SVT produced by reentry by the accessory pathway in 42% of cases. Long-term oral administration (17 +/- 3.7 months) of the same dose prevents 88% of SVT produced by internodal reentry and 80% of spontaneous SVT produced by reentry by the accessory pathway. Cardiologic tolerance is satisfactory: one case of atrioventricular and intraventricular dysrhythmia is observed. The same holds true for general tolerance: in 2 cases drug administration is discontinued and 11 patients present neurologic and digestive troubles improving after lowering the dosage or increasing the fractionation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Treatment of paroxysmal reentrant supraventricular tachycardia with flecainide acetate

The electrophysiologic effects and therapeutic efficacy of intravenous and oral flecainide were studied in 15 patients with spontaneous and inducible sustained paroxysmal supraventricular tachycardia (SVT). Twelve patients had atrioventricular (AV) reentrance using an accessory pathway for retrograde conduction and 3 had AV nodal reentrance. Fourteen patients received intravenous flecainide (2 mg/kg body weight over 15 minutes) during an initial electrophysiologic study. Nine patients were restudied during oral flecainide administration (200 to 400 mg/day). After intravenous or oral flecainide therapy, reentrant SVT was noninducible in 6 patients with AV reentrance and in the 3 with AV nodal reentrance. In these 9 patients, intravenous flecainide prevented induction of reentrant SVT by depressing conduction over the retrograde limb of the reentry circuits. In the 6 patients with inducible sustained AV reentrant SVT before and after flecainide therapy, the cycle length of tachycardia increased significantly, mainly as the result of an increase in ventriculoatrial conduction time. There was concordance between the intravenous and the oral effects of flecainide on the mechanism of the SVT. Twelve patients continued oral flecainide treatment for a mean of 16 months (range 5 to 28). Tachycardia recurred in 3 of 4 patients whose arrhythmia remained inducible after flecainide therapy and in 1 of 8 patients whose SVT was suppressed. It is concluded that flecainide is an effective and convenient antiarrhythmic agent to treat patients who have AV nodal or AV reentrant SVT.     

Preexcitation masking underlying aberrant conduction: an atriofascicular accessory pathway functioning as an ectopic right bundle branch.

Preexcitation and aberrant conduction both cause a broad QRS complex. An unusual case of an atriofascicular accessory pathway effectively functioning as an ectopic right bundle branch and responsible for both physiologically normal ventricular activation and pathologic preexcited tachycardias as part of a split AV node-bundle branch system is presented.     

Variants of Preexcitation—Specialized Atriofascicular Pathways, Nodofascicular Pathways, and Fasciculoventricuiar Pathways:

Variants of Preexcitation. introduction: In the present report, the electrophysiiologic findings in patients with different types of variants of preeexcitwtion, i.e., atriofascicualr, nodofacicular, and fasciculoventricular fibers, and the results of radiofrequency catheter ablation using different target sites are described. Methods and Results: Twelve patients (mean age 36 ± 17 years) with variants of the preexcitation syndromes underwent electrophysiologic study and radiofrequency catheter ablation. The atrial origin of atriofascicular pathways remote from the normal AV node was assessed by application of late atrial extrastimuli that advanced (“reset”) the timing of the next QRS complex without anterograde penetration into the AV node. In patients with atriofacicular pathways, ablation of the accessory pathway or the retrograde fast AV node pathway was attempted. Ablation of the atriofascicular pathways was guided by a stimulus-delta wave interval mapping in the first live patients and by recording of atriofascicular pathway activation potentials in the next five patients. A nodofascicular pathway was suggested if VA dissociation occurred during tachycardia and if atrial extrastimuli failed to reset the tachycardia without anterograde penetration into the AV node. A fasciculoventricular connection was suggested if the proximal insertion of the accessory pathway was found to arise from the His bundle or bundle branches. The PR interval was expected within normal limits during sinus rhythm and the QRS complex to he slightly prolonged with a discrete slurring of the R wave, suggesting a small delta wave. Ten of the 12 patients had evidence for atriofascicular pathways and one patient each for a nodofascicular and fasciculoventricular pathway. In six patients, the atriofascicular pathways were successfully ablated, and in two patients, the retrograde fast AV node pathway. In one patient, a concealed right posteroseptal accessory AV pathway served as the retrograde limb and was successfully ablated. The nodofascicular pathway was shown to he a bystander during AV node reentrant tachycardia. After successful fast AV node pathway ablation resulting in marked PR prolongation, no preexcitation was present during sinus rhythm because of the proximal insertion of the nodofascicular pathway distal to the delay producing parts of the AV node. The proximal insertion of the fasciculoventricular pathway was suggested to arise distal to the AV node at the site of the penetrating AV bundle. The earliest ventricular activation at the His-bundle recording site indicated the ventricular insertion of this accessory connection into the ventricular summit. The fasciculoventricular connection gave rise to a fixed ventricular preexcitation and served as a bystander during orthodromic AV reentrant tachycardia incorporating a left-sided accessory AV pathway.     

Regelm??ige Tachykardien mit breitem Kammerkomplex

Differential diagnosis of regular tachycardia with broad QRS complex can be challenging in daily practice. There are four different arrhythmias that have to be taken into account when being confronted with a broad QRS complex tachycardia: (1) ventricular tachycardia (VT); (2) supraventricular tachycardia (SVT) with bundle branch block (BBB); (3) SVT with AV conduction over an accessory AV pathway; (4) paced ventricular rhythm. Due to potentially fatal consequences, the correct diagnosis is important in view of both the acute treatment and the long-term therapy. Since SVT with accessory conduction is rare and a paced ventricular rhythm can be identified easily by stimulation artifacts, in most cases, a VT has to be differentiated from an SVT with BBB. Several ECG criteria can be helpful: (1) QRS complex duration > 140 ms in right BBB tachycardia or > 160 ms in left BBB tachycardia; (2) ventricular fusion beats; (3)“Northwest” QRS axis; (4) ventriculoatrial dissociation; (5) absence of an RS complex or RS interval > 100 ms in leads V₁-V₆; (6) a positive or negative concordant R wave progression pattern in leads V₁-V₆; (7) absence of an initial R wave or an S wave in lead V₁ in right BBB tachycardia; (8) absence of an R wave or an R/S ratio < 1 in lead V₆ in right BBB tachycardia; (9) absence or delay of the initial negative forces in lead V₁ in left BBB pattern (R wave duration > 30 ms in V₁; interval between onset of R wave and Nadir of S wave > 60 ms in V₁); (10) presence of Q wave. Any of these variables favor VT. However, none of the criteria has both a sufficient sensitivity and specificity when utilized on its own. Therefore, various diagnostic algorithms have been proposed using a number of the above criteria consecutively. By doing so, the specificity and sensitivity of correctly identifying a VT or an SVT with BBB can be raised to > 95%.     

Surface electrocardiographic clues suggesting presence of a nodofascicular Mahaim fiber

Standard electrocardiograms from 87 consecutive patients with tachycardia of left bundle branch block configuration were analyzed retrospectively for features that might be characteristic of tachycardia utilizing a nodofascicular Mahaim fiber. The study group consisted of 13 patients with nodofascicular tachycardia, 34 with supraventricular tachycardia and aberrant conduction over the His-Purkinje system, 22 with ventricular tachycardia and 18 with antidromic tachycardia utilizing a right-sided accessory atrioventricular pathway. Six variables present during tachycardia of left bundle branch block configuration were predictive of a nodofascicular fiber: cycle length between 220 and 450 ms, QRS axis of 0 to -75 degrees, QRS duration 0.15 second or less, R wave in lead I, rS wave in precordial lead V1 and a precordial transition from a negative to a positive QRS complex after lead V4. All six criteria were present in 16 of the 87 patients. No patient with ventricular tachycardia satisfied these criteria, whereas 3 of 34 with supraventricular tachycardia, 1 of 18 with antidromic tachycardia and 12 of 13 with tachycardia using a nodofascicular fiber did. It is concluded that analysis of the surface electrocardiogram during tachycardia may suggest the presence of a nodofascicular fiber.     

Minimally decremental atriofascicular accessory pathway with bidirectional conduction

Atriofacicular pathways of Mahaim type are typically decrementally conducting accessory pathways without retrograde conduction properties, located on the right ventricular free wall at the tricuspid annulus. We report a patient with an atriofascicular pathway with minimal anterograde decremental conduction. Both long and short V-H antidromic atriofascicular reentrant tachycardias were induced and mechanism confirmed with electrophysiologic testing. Additionally, orthodromic atriofascicular reentrant tachycardia with narrow and right bundle branch block morphologies were inducible. Mahaim pathway was successfully ablated with elimination of both antidromic and orthodromic tachycardias.     

Wolff-Parkinson-White syndrome in children: electrophysiologic and pharmacologic characteristics.

Intracardiac electrophysiologic studies were performed on 28 infants and children, ages 1 month to 18 years, with the Wolff-Parkinson-White syndrome to try to determine 1) the electrophysiologic characteristics of the accessory connection and 2) the mechanisms of associated supraventricular dysrhythmias. Although the antegrade refractory periods of the normal conduction system were shorter than those found in adults, those of the accessory connection were slightly longer. Reciprocating supraventricular tachycardia (SVT), which had been a clinical problem in 26 of 28, could be induced in the laboratory in all 26 subjects. The mechanism involved reentry with antegrade conduction through the atrioventricular (AV) node and retrograde through the accessory connection in 22. Eleven of these 22 had a wide QRS during tachycardia due to a bundle branch block. Three other subjects had wide QRS tachycardia, but the mechanism involved antegrade conduction through the accessory connection and retrograde through the AV node. The other patient had AV node reentry tachycardia. Two patients did not have clinical SVT, and in these two, SVT could not be induced. Neither patient had retrograde conduction through the accessory connection. The site of the accessory connection could be identified in 26 subjects by the sequence of retrograde activation of the atrium during SVT or ventricular pacing. Digitalis shortened the refractory period of the accessory connection in five of the eight patients studied.