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.

Comparison of electrophysiological characteristics of right- and left-sided Mahaim-type accessory pathways.

AIMS: Mahaim-type accessory pathways (MAPs) are generally right-sided due to the embryological differentiation, but left-sided localization is also possible. This study aims to compare the clinical and electrophysiological characteristics of right- and left-sided MAPs. METHODS: Of 251 patients diagnosed with AP by electrophysiological study between November 2015 and February 2020, 12 patients with MAP were included (right sided n = 8, left sided n = 4). MAP was diagnosed if; (1) no retrograde conduction; (2) anterograde decremental conduction; (3) adenosine sensitivity; and (4) Mahaim potential at successful ablation site were present. RESULTS: Ten of twelve MAPs were clustered on the lateral walls of the mitral (n = 3, 75%) and tricuspid annuli (n = 7, 87.5%). Right-sided MAPs were mostly long pathways extending toward the conduction system whereas left-sided MAPs were short extending toward the neighboring myocardium. For right- and left-sided APs, the median QRS times were 129 and 156 ms (p = .042), the median VAbl -RVApex intervals were -12 and 64 ms (p = .007), the median QRS-V(His) intervals were 16 and 86 ms (p = .120), and the median VAbl -QRS interval was -8 and 12 ms (p = .017), respectively. Coexistence of dual atrioventricular node physiology was observed only in right-sided APs (n = 3, 37.5%). CONCLUSION: MAPs are more typically located on the right but may rarely be seen on the left. Catheter ablation was associated with high success without complications.

Mahaim pathway potential revealed by high-resolution three-dimensional mapping.

Mapping and ablation of atriofascicular fibers can be highly challenging due to the complex and dynamic anatomy of the tricuspid valve annulus. This case highlights the utility of a multi-electrode catheter three-dimensional mapping approach to localize the Mahaim pathway along the tricuspid annulus in order to guide catheter ablation.

Part II-Clinical presentation, electrophysiologic characteristics, and when and how to ablate atriofascicular pathways and long and short decrementally conducting accessory pathways.

Recognition of the presence, location, and properties of unusual accessory pathways for atrioventricular conduction is an exciting, frequently difficult, challenge for the clinical cardiac arrhythmologist. In this second part of our series of reviews relative to this topic, we discuss the steps required to achieve the correct diagnosis and appropriate management in patients with the so-called "Mahaim" variants of pre-excitation. We indicate that, nowadays, it is recognized that these abnormal rhythms are manifest because of the presence of atriofascicular pathways. These anatomical substrates, however, need to be distinguished from the other long and short accessory pathways which produce decremental atrioventricular conduction. The atriofascicular pathways, along with the long decrementally conducting pathways, have their atrial components located within the vestibule of the tricuspid valve. The short decremental pathways, in contrast, can originate in the vestibules of either the mitral or tricuspid valves. As a starting point, careful analysis of the 12-lead electrocardiogram, taken during both sinus rhythm and tachycardias, should precede any investigation in the catheterization room. When assessing the patient in the electrophysiological laboratory, the use of programmed electrical stimulation from different intracardiac locations, combined with entrainment technique and activation mapping, should permit the establishment of the properties of the accessory pathways, and localization of its proximal and distal ends. This should provide the answer to the question "is the pathway incorporated into the circuit underlying the clinical tachycardia". That information is essential for decision-making with regard to need, and localization of the proper site, for catheter ablation.

Unusual variants of pre-excitation: From anatomy to ablation: Part III-Clinical presentation, electrophysiologic characteristics, when and how to ablate nodoventricular, nodofascicular, fasciculoventricular pathways, along with considerations of permanent junctional reciprocating tachycardia.

The recognition of the presence, location, and properties of unusual accessory pathways for atrioventricular conduction is an exciting, but frequently a difficult, challenge for the clinical cardiac arrhythmologist. In this third part of our series of reviews, we discuss the different steps required to come to the correct diagnosis and management decision in patients with nodofascicular, nodoventricular, and fasciculo-ventricular pathways. We also discuss the concealed accessory atrioventricular pathways with the properties of decremental retrograde conduction that are associated with the so-called permanent form of junctional reciprocating tachycardia. Careful analysis of the 12-lead electrocardiogram during sinus rhythm and tachycardias should always precede the investigation in the catheterization room. When using programmed electrical stimulation of the heart from different intracardiac locations, combined with activation mapping, it should be possible to localize both the proximal and distal ends of the accessory connections. This, in turn, should then permit the determination of their electrophysiologic properties, providing the answer to the question "are they incorporated in a tachycardia circuit?". It is this information that is essential for decision-making with regard to the need for catheter ablation, and if necessary, its appropriate site.

Mahaim Tachycardia Induced Cardiomyopathy.

We present the case report of a 22-year man, with incessant palpitations, chest pain, shortness of breath, and pulsations in his neck for the past 7 months. He was referred to the cardiology unit for workup of wide complex tachycardia (WCT). His echocardiography, 6 months earlier, had demonstrated severe left ventricular (LV) systolic dysfunction, severe global hypokinesia, mild tricuspid regurgitation (TR), and mild mitral regurgitation (MR) which resolved with medical therapy including beta-blockers. He underwent electrophysiological study, which revealed a decremental right sided atriofascicular pathway causing a WCT with left bundle branch block (LBBB) morphology and left axis deviation (LAD, Mahaim tachycardia). This was successfully ablated by radiofrequency ablation (RF) with abolition of the tachycardia. This case report highlights Mahaim tachycardia induced cardiomyopathy, a rare but curable cause of cardiomyopathy.

Electroanatomic mapping guided cryoablation of Mahaim pathways in children with limited fluoroscopy exposure.

BACKGROUND: The presence of Mahaim accessory pathways (MAP) with anterograde decremental conduction is a disorder that leads to antidromic atrioventricular reentrant tachycardia. There are rare reports of cryoablation use in MAP. This study aims at sharing our experience with using cryoablation to treat MAP in children. METHODS: Electrophysiology study and catheter ablation were performed in 14 patients diagnosed with Mahaim tachycardia between January 2010 and December 2013. Cryoablation was used in nine of the cases. A three-dimensional navigation system with surface electrode patches (EnSite System, St. Jude Medical Inc., St. Paul, MN, USA) was used for all procedures. RESULTS: The patients (two girls and seven boys) had a median age of 11.5 years (8-18 years) and a median weight of 67 kg (31-80 kg). Mahaim conduction was localized in the right posterolateral (n = 4), right lateral region (n = 2), right posteroseptal (n = 1), right anterolateral (n = 1), and right anterior (n = 1). A pathway potential was noted in six of nine cases at the tricuspid annulus. Catheter choices and acute success rates were as follows: cryoablation in four (three of four successful), radiofrequency catheter ablation (RFA) and cryoablation in five (successful in four of five). No fluoroscopy was used in six of nine patients. The mean procedure duration was 249 ± 90 minutes. No major complications were observed. The final long-term success rate for cryoablation was seven of nine (78%). CONCLUSIONS: Cryoablation can be used as a reliable and effective alternative to RFA in the treatment of Mahaim accessory conduction pathways in children. Prospective comparative studies are necessary in order to further evaluate the long-term efficacy of this method.

Successful cryoablation of Mahaim tachycardia in a child with Ebstein's anomaly.

Mahaim fibers with decremental atrioventricular (AV) node-like conduction properties comprise less than 3 % of accessory pathways. Radiofrequency ablation of right atriofascicular pathways guided by a distinct Mahaim potential detected at the anterolateral to posterolateral tricuspid annulus or in the right ventricular free wall is a safe and highly effective treatment method. The case report presents a 16-year-old boy with Ebstein's anomaly and symptomatic wide complex tachyarrhythmia. The electrophysiologic study and the entire ablation procedure were performed using a three-dimensional mapping system (EnSite Velocity; St. Jude Medical Inc., St. Paul, MN, USA). No fluoroscopy was used during the procedure. Electrophysiologic evaluation demonstrated typical atrioventricular nodal reentrant tachycardia and Mahaim tachycardia with a wide QRS and a left bundle branch block pattern. After Mahaim potential was located at the lateral tricuspid annulus, successful cryoablation was performed with an 8-mm-tip catheter followed by slow pathway ablation to eliminate typical atrioventricular nodal reentrant tachycardia. Cryoablation with an 8-mm-tip catheter can be an alternative treatment option for children with Mahaim tachycardia.

Electroanatomic localization of a slowly conducting atrioventricular (Mahaim) accessory pathway.

We present a case of a 34-year-old female with Ebstein's anomaly and symptomatic wide complex tachyarrhythmia. Electrophysiologic evaluation demonstrated antidromic tachycardia utilizing a right-sided decremental, slowly conducting atrioventricular pathway. Distinct accessory pathway potentials along the length of the bypass tract were sequentially recorded to define the anatomic course of the pathway, as uniquely represented on a three-dimensional electroanatomic map, and to successfully guide catheter ablation.

Nodoventricular pathway associated with twin AV nodes: complexity of ablation in single ventricle physiology.

We report the case of a patient with heterotaxy syndrome including complex single ventricular morphology and interrupted IVC in association with twin conduction systems and a nodoventricular accessory pathway connection. The presence of 3 distinct QRS morphologies was inadvertently discovered during a hemodynamic catheterization study and prompted formal EP testing prior to hepatic venous inclusion into the Fontan circuit and loss of access to the atrial chamber for testing and therapy. This patient underscores the importance of close surveillance and high index of suspicion of arrhythmia mechanisms in patients with heterotaxy syndrome in conjunction with single ventricle morphology.

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.

Electrophysiology study and radiofrequency catheter ablation of atriofascicular tracts with decremental properties (Mahaim fibre) at the tricuspid annulus.

AIMS: The aim was to study the common mapping methods for Mahaim fibre and their role in radiofrequency (RF) ablation. METHODS AND RESULTS: Fifteen patients having Mahaim fibre tachycardia underwent electrophysiological study. Mahaim fibre mapping methods like (i) Mahaim potential (M), (ii) shortest atrial stimulus-to-pre-excitation (STP), and (iii) mechanical trauma induced loss of conduction were studied. Accessory pathway mapping was performed by M potential in 10 patients (67%), shortest atrial STP in 3 patients (20%), and mechanical trauma in 2 patients (13%). Mahaim fibre was localized at right atrial freewall of tricuspid annulus (8-10 o'clock) in 13 patients (87%), at 6.30 o'clock in one patient, and at 5 o'clock in 1 patient. Fourteen patients underwent RF ablation. Thirteen patients had complete loss of conduction over accessory pathway and one had partial modification with a conduction delay. Radiofrequency ablation was not performed in one patient (shortest STP group) due to its closeness to the compact atrioventricular node. Mahaim junctional acceleration during RF ablation was observed in all patients of M potential, 1 patient of mechanical trauma, and none of the atrial STP group. One patient (M potential group) had tachycardia recurrence during follow-up. CONCLUSION: Mahaim fibre is commonly located between 8 and 10 o'clock at tricuspid annulus. M potential guides to successful RF ablation in most patients. Mahaim junctional acceleration is commonly seen during RF ablation guided by M potential map.