Epicardial mapping in patients with "nodoventricular" accessory pathways

Comprehensive assessment of Mahaim accessory pathways' anatomic distribution

Objective

To present the authors’ experience of Mahaim-type accessory pathways (MAPs), focusing on anatomic localizations.

Methods

Data from consecutive patients who underwent electrophysiological study (EPS) for MAP ablation in two tertiary centres, between January 1998 and June 2020, were retrospectively analysed.

Results

Of the 55 included patients, 27 (49.1%) were male, and the overall mean age was 29.5 ± 11.6 years (range, 12–66 years). MAPs were ablated at the tricuspid annulus in 43 patients (78.2%), mitral annulus in four patients (7.3%), paraseptal region in three patients (5.5%), and right ventricle mid-apical region in five patients (9.1%). Among 49 patients who planned for ablation therapy, the success rate was 91.8% (45 patients).

Conclusion

MAPs were most often ablated at the lateral aspect of the tricuspid annuli, sometimes at other sides of the tricuspid and mitral annuli, and infrequently in the right ventricle. The M potential mapping technique is likely to be a useful target for ablation of MAPs.

Ablating the ventricular insertion of atrio-fascicular Mahaim fiber: what selection criteria should we use?

We reported a patient who underwent RF ablation of the distal insertion of an atrio-fascicular accessory pathway with decremental properties because of inability to map a suitable potential alongside the tricuspid annulus. Small, discrete potentials resembling those of purkinje fiber were found at right ventricular apex, all these potentials showed early activation during tachycardia preceding the QRS onset of various degrees. Pace mapping helped to localize the presumed main distal insertion of the atrio-fascicular AP in a region where a damage of the His-purkinje system may ensue. This case report describes catheter ablation of an atriofascicular accessory pathway by targeting its distal (ventricular) insertion site.

Atriofascicular Pathways: Where to Ablate?

BACKGROUND

Atriofascicular accessory pathway (AP), often referred to as Mahaim pathway, is an uncommon form of preexcitation. The usual target for ablation is at the site of a high-frequency potential along the tricuspid annulus (TA). We present our observations in mapping and ablation of 29 patients with atriofascicular APs.

METHODS AND RESULTS

Twenty-nine consecutive patients who underwent radiofrequency ablation (RFA) for atriofascicular pathways comprised the series. Demographic factors, clinical features of the tachycardia, ablation site, and results were analyzed. The mean age was 19 +/- 8 years; 15 were men. Three patients had Ebstein's anomaly of the tricuspid valve. Four patients had an additional AP and two patients had concomitant typical atrioventricular nodal reentrant tachycardia. RFA was successful in 28 patients (97%); repeat ablation was required in two patients. The site of successful ablation was on the TA at the site of a sharp, high frequency potential in 15 patients (52%). In the remaining 14 patients, a potential was not found along the TA, and ablation was targeted at the ventricular insertion of the AP into the distal right bundle. At the successful ventricular ablation site, local ventricular activation preceded the surface electrocardiogram by 20 +/- 6 ms. Eight of the 14 patients (57%) undergoing ablation in the ventricle, developed right bundle branch block (RBBB). One patient who underwent successful ablation along the TA also manifested RBBB after ablation; however, this patient had Ebstein's anomaly and preexcitation had completely masked the RBBB. The mean procedure and fluoroscopy time was 150 +/- 32 and 35 +/- 12 minutes, respectively.

CONCLUSIONS

In atriofascicular pathways, an AP potential was found along the TA in only 52% of patients. Ablation at the ventricular insertion site often resulted in RBBB (57%), but the AP was also successfully ablated.

Variability in the manifestation of pre-excited atrial fibrillation: its quantification, theoretical origin, and diagnostic potential

BACKGROUND

Irregular broad complex tachycardia (BCT) may be due to atrial fibrillation (AF) occurring in the presence of ventricular pre-excitation (pre-excited AF) or bundle branch block (BBB-AF). While irregularity is a defining characteristic of AF, it is a common subjective impression that greater variability in manifestation exists for pre-excited AF than BBB-AF. This difference can potentially be exploited for distinguishing the two conditions if some means can be found to quantify it.

METHODS

For each of 75 ECGs showing irregular BCT (41 pre-excited AF and 34 BBB-AF), a random sample of 10 distinct QRS complexes were selected for quantitative measurement of variability in manifestation, which included the standard deviation (SD) of the width, the SD of the axis, and the coefficient of variation (CV) of the amplitude of the QRS complex.

RESULTS

Pre-excited AF showed statistically significantly greater values than BBB-AF with respect to these measures, and receiver-operating characteristic curves showed that these differences could be useful for their discrimination. For the SD of QRS width, a cut-off value of 8 ms appeared optimal (sensitivity 1.00 and specificity 0.79). For the SD of QRS axis, a cut-off value of 2.5 degrees appeared optimal (sensitivity 0.84 and specificity 0.56). For the CV of QRS amplitude, a cut-off value of 0.10 appeared optimal (sensitivity 0.82 and specificity 0.76).

CONCLUSIONS

Pre-excited AF demonstrated greater variability than BBB-AF in manifestation. The measures of variability developed can potentially be useful for diagnosing irregular BCT in practice, especially in the context of automated computer-aided diagnosis.

Electrocardiographic criteria for diagnosis of irregular broad complex tachycardia with a high sensitivity for preexcited atrial fibrillation

AF may appear as an irregular broad complex tachycardia (BCT) if atrioventricular conduction occurs via an accessory pathway (preexcited AF) or if bundle branch block (BBB), preexistent or rate related, exists in the His-Purkinje system (BBB-AF). While BBB-AF is relatively benign, preexcited AF may herald sudden cardiac death. Hence it is important that the two conditions can be reliably distinguished. Yet, there is no preexistent algorithms for this purpose. Griffith et al. previously proposed a simple algorithm for a similar problem, that of distinguishing the two differential diagnoses for regular BCT: VT and SVT with BBB, on the basis that unless the QRS morphologies in V1 and V6 are absolutely typical of BBB, VT will be diagnosed. The authors propose an extrapolation of this principle to irregular BCT by stating that, unless the QRS morphologies in V1 and V6 are absolutely typical of BBB, preexcited AF will be diagnosed. Seventy-five ECGs showing irregular BCT (41 preexcited AF and 34 BBB-AF) were shown to two fellows in electrophysiology who were given no other information and were instructed to diagnose preexcited AF unless the QRS morphology pattern was typical of BBB. Observer 1 achieved a sensitivity of 100% (41/41) and a specificity of 79% (27/34), while observer 2 achieved a sensitivity of 100% and a specificity of 85% (29/34). By QRS morphology pattern, an average sensitivity of 100% and specificity of 82% were achieved for the diagnosis of irregular BCT. The algorithm is simple and easy to implement and recommended for clinical use.

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.

New electrophysiologic features and catheter ablation of atrioventricular and atriofascicular accessory pathways: evidence of decremental conduction and the anatomic structure of the Mahaim pathway

INTRODUCTION

Several modalities of catheter ablation have been proposed to eliminate Mahaim pathway conduction. However, limited research has been reported on the electrophysiologic nature of this pathway in its entity.

METHODS AND RESULTS

In seven patients, electrophysiologic study was performed, and radiofrequency energy was applied to investigate the electrophysiologic clues for successful ablation. In all seven patients, the Mahaim pathway was diagnosed as a right-sided atriofascicular or atrioventricular pathway with decremental properties. In two patients, two different kinds of electrograms were recorded through the ablation catheter positioned at the Mahaim pathway location: one was suggestive of conduction over the decremental portion, demonstrating a dulled potential; and the other of nondecremental conduction, demonstrating a spiked potential. All but one of the Mahaim pathways were eliminated successfully at the atrial origin where the spiked Mahaim potential was recorded. Radiofrequency energy application was performed at the slow potential site resulting in failure to eliminate the conduction over the Mahaim pathway. Conduction block at the site between the slow and fast potential recording sites was provoked by intravenous administration of adenosine, concomitant with a decrease in the amplitude of the Mahaim potential. In one patient, the clinical arrhythmia was a sustained monomorphic ventricular tachycardia originating from the ventricular end of the Mahaim fiber.

CONCLUSION

The identification of Mahaim spiked potentials may be the optimal method to permit their successful ablation. Detailed electrophysiologic assessment is indispensable for successful ablation of tachycardias associated with Mahaim fibers because tachycardias unassociated with Mahaim fibers can occur despite complete elimination of the Mahaim fiber.

Radiofrequency catheter ablation of atriofascicular accessory pathways guided by discrete electrical potentials recorded at the tricuspid annulus

BACKGROUND

The purpose of this study was to test the feasibility of using the recording of discrete electrical potentials to guide radiofrequency catheter ablation of atriofascicular accessory pathways with Mahaim-like properties.

METHODS AND RESULTS

Four patients (3 females, 1 male) who fulfilled criteria for having atriofascicular accessory pathways with Mahaim-like properties and preexcited reciprocating tachycardia underwent radiofrequency catheter ablation. The mean age was 35 years (range 27-47). Symptoms were present for a mean of 10.5 years (range 6-18). Recording of discrete electrical potentials of the atriofascicular pathway was attempted by mapping the tricuspid annulus in sinus rhythm, during atrial pacing, and during reciprocating tachycardia. During atrial pacing, a mean of seven radiofrequency pulses (range 1-14), delivered to the tricuspid annulus at the area where electrical potentials were recorded, eliminated conduction through the atriofascicular accessory pathway in all patients. No complications occurred. Tachycardia did not reoccur during a mean follow-up of 5 months (range 3-9).

CONCLUSIONS

Recording of discrete electrical potentials at the tricuspid annulus identifies an optimal ablation site where radiofrequency current can safely eliminate conduction through atriofascicular accessory pathways with Mahaim-like properties.

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.

Radiofrequency ablation therapy in concealed left free wall accessory pathway with decremental conduction

An electrophysiologic study followed by transcatheter radiofrequency ablation therapy was performed in two adult patients with a permanent form of junctional tachycardia. Both patients had no structural heart disease and exhibited a normal resting ECG. The P wave during tachycardia was negative in leads 1, 3, and aVF, biphasic over V6, and positive in V1 and aVL in both patients, while the P-R/R-P interval ratio during tachycardia was 0.82 and 0.36, respectively, in both patients. Both patients displayed an eccentric atrial activation sequence with the earliest atrial activation occurring at the distal coronary sinus and a decremental retrograde conduction property during incremental ventricular pacing, suggesting the presence of a concealed slowly conducting left free wall accessory pathway. The tachycardia used the normal atrioventricular pathway for anterograde conduction and the concealed show left accessory pathway for retrograde conduction. It was terminated following adenosine administration in both patients; termination of tachycardia was due to a block in the retrograde accessory pathway in one patient and due to a block in the atrioventricular node in the other patient. Radiofrequency ablation was performed by the retrograde transaortic approach. The radiofrequency f4p4ent was delivered to the site of the earliest atrial activation during tachycardia at the ventricular aspect of the mitral annulus. The successful ablation site had a ventriculoatrial (VA) interval of 120 and 130 ms, respectively, and was located at the posterolateral and lateral aspects of the mitral annulus. Following ablation, there was no VA conduction; however, conduction through the normal atrioventricular pathway was noted during isoproterenol infusion in both patients. There was no induction of tachycardia. This study demonstrates that the permanent form of junctional tachycardia in adults can incorporate a concealed left free wall accessory pathway with a decremental property. Radiofrequency ablation therapy is effective and safe in this form of arrhythmia.

Radiofrequency catheter ablation of atriofascicular and nodoventricular Mahaim tracts

BACKGROUND

Several mechanisms have been proposed to explain the pathogenesis of tachycardia in patients with Mahaim tracts. The tachycardia may involve antegrade conduction over an atriofascicular pathway with decremental properties or a nodofascicular pathway.

METHODS AND RESULTS

We report six patients with recurrent episodes of preexcited tachycardia with findings consistent with "Mahaim tract" conduction. All patients exhibited decremental antegrade preexcited conduction with atrial pacing and a preexcited tachycardia with initial activation of the proximal right bundle branch. In four patients (group 1), atrial premature complexes (APCs) induced at the tricuspid annulus just after the inscription of the septal atrial electrogram and during left bundle branch block preexcited tachycardia advanced the next preexcited ventricular complex. In these patients, discrete Mahaim potentials were inscribed over the right anterolateral or lateral tricuspid annulus. Two patients (group 2) had evidence of dual atrioventricular nodal conduction. APCs during left bundle branch block tachycardia just after inscription of the septal atrial electrogram failed to advance the next ventricular complex with similar preexcited morphology, and no Mahaim potentials could be recorded from the tricuspid annulus. In group 1 patients, application of radiofrequency energy to sites recording the Mahaim potentials resulted in tachycardia cure. For patients in group 2, selective slow atrioventricular nodal pathway ablation in the midseptal region resulted in complete ablation of both the slow atrioventricular nodal pathway and Mahaim conduction in two patients.

CONCLUSIONS

Mahaim tachycardia can be due to atriofascicular pathways, which may be ablated over the right tricuspid annulus, or to septal pathways, which may arise from the slow atrioventricular nodal pathway in patients with dual atrioventricular nodal physiology. In the latter circumstance, successful ablation is achieved by placing the lesion in the midseptal region.

Operation for the Wolff-Parkinson-White syndrome in the catheter ablation era

Catheter ablation has greatly altered surgical referral patterns for the Wolff-Parkinson-White syndrome. We describe 51 patients (aged 9 to 63 years; 35 male, 16 female) referred for operation from our institution and elsewhere between August 1990 and August 1993, coincident with the inception of our ablation program. During the same period, 375 patients with problematic Wolff-Parkinson-White syndrome had ablation procedures. Operation was the initial therapy in 26 patients, due to physician preference in 23 and the need for a concomitant cardiac operation in 3. Operation was related to ablation failure in 22 patients and was urgent in 3 patients. Previous ablation was not associated with added surgical difficulties, and all pathways were ablated intraoperatively on the first attempt using the epicardial approach. Visible epicardial lesions were observed in 8 patients at the site of the accessory pathway. In 2 patients, the lesions were remote to the atrioventricular ring. There was a striking significant increase in proportion of right free wall pathways after attempted ablation (27% versus 8%) as compared with the preablation era. We conclude that previous attempted ablation does not impair efficacy and safety of operative therapy. Operation remains a useful alternative for ablation failure and as a back-up for acute complications.

Anterograde and retrograde decremental conduction over left-sided accessory atrioventricular pathways in the Wolff-Parkinson-White syndrome

The electrophysiologic properties of left-sided accessory pathways (APs) were examined by cardiac stimulation in 55 patients with Wolff-Parkinson-White syndrome. Atrioventricular and ventriculoatrial conduction times were assessed at the coronary sinus level nearest to the AP and then plotted graphically as a function of coupling interval (for atrial and ventricular refractory period determinations). Of 29 patients with anterograde conduction over the AP, 10 (34%) exhibited decremental conduction. However, only two (7%) had a maximal decrement equal to or more than 30 msec. In the other eight (27%) patients the maximal decrement ranged from 10 to 20 msec. The longest coupling interval at which anterograde decremental conduction was demonstrated ranged from 260 to 440 msec (346 +/- 52 msec). The shortest coupling interval ranged from 240 to 320 msec (265 +/- 24 msec). The anterograde decremental conduction zone was 91 +/- 55 msec. Of 51 patients with retrograde conduction over the AP, 23 (45%) exhibited decremental conduction. However, only eight (15%) had a maximal decrement equal to or greater than 30 msec. In the other 15 (29%) patients the maximal decrement ranged from 10 to 25 msec. The longest coupling interval was 338 +/- 70 msec. The shortest coupling interval was 275 +/- 42 msec. The retrograde decremental conduction zone was 72 +/- 47 msec. There was a significant inverse correlation between the AP effective refractory period and the maximal decrement (r = -0.42; p < 0.05). The comparison of maximal ventriculoatrial conduction time with the maximal decrement revealed a positive correlation (r = 0.63; p < 0.01). These data reveal that minimal decremental conduction over left-sided APs is not an uncommon finding and stress that care should be taken in evaluation of conduction over these connections.

Variable location of accessory pathways associated with the permanent form of junctional reciprocating tachycardia and confirmation with radiofrequency ablation

Permanent junctional reciprocating tachycardia (PJRT) occurs primarily in young patients and causes nearly incessant tachycardia that is frequently refractory to pharmacologic treatment. Previous nonpharmacologic therapy has included surgical or direct-current catheter ablation of either the His bundle or the accessory pathway. The accessory pathway in PJRT has been described as having retrograde and anterograde decremental conduction properties, and is typically identified in the posteroseptal location. This report describes radiofrequency catheter ablation of accessory pathways in 8 patients with PJRT. All ablations were successful and without adverse effects. Accessory pathway potentials were detected just before atrial activation in 6 of 8 patients. A new finding was that 5 of the 8 pathway locations, as identified by the site of successful ablation, were not in the typical posteroseptal region. In 1 patient it was located in the right posteroseptal region, 2 were in the right atrial freewall, 1 was in the right anterior septum and 1 was in the left posterior region just outside of the septal region. In conclusion, radiofrequency catheter ablation can be a highly effective and safe method for treatment of young patients with PJRT. Because the accessory pathways can be located outside of the posteroseptal region, careful mapping of both the right and left atrioventricular groove may be necessary for successful ablation.

Accessory atrioventricular node and bundle: a cause of antidromic reentry tachycardia

Two patients are described with antidromic reentry tachycardia successfully treated by interruption of an anterior septal accessory atrioventricular node and bundle. This anomalous connection resembles an atrioventricular conduction sling seen in complex congenital heart malformations. It has atrioventricular node-like properties, is located in the anterior septal area, will only conduct antegrade, and has an insulated connection to the right bundle branch. Rather than nodoventricular, nodofascicular, atriofascicular, or Mahaim, a more appropriate label for the connection is accessory atrioventricular node and bundle.