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......................................................................... tend to occur more frequently in younger patients than in those with AVNRT; however, significant overlap exists.3 Concealed APs are predominantly localized along the left free wall (64%), and less frequently at septal (31%) and right free wall locations.395 Clinical presentation is with AVRT. Concealed pathways are not associated with an increased risk of sudden cardiac death. The management of AVRT due to a concealed AP is similar to that of an overt AP, but in this case is related to symptoms without significant prognostic relevance in most cases.

11.3.8 Permanent junctional reciprocating tachycardia PJRT is a rare form of AV reciprocating tachycardia using a concealed AP. Usually these APs, originally described by Coumel, are located in the posteroseptal region and are associated with retrograde decremental conduction properties.407 PJRT is a long RP tachycardia due to the slow conduction properties of the AP, and is characterized by deeply inverted retrograde P waves in leads II, III, and aVF due to the retrograde nature of atrial activation. The incessant nature of PJRT may result in TCM that usually resolves after successful treatment by radiofrequency catheter ablation, particularly in younger patients.407,408 Catheter ablation is strongly recommended in symptomatic patients or in cases with impaired LV ejection fraction likely related to TCM. Other potential causes of long RP tachycardias are sinus tachycardia, AT, atypical AVRT, and JET with 1:1 retrograde conduction.

11.3.9 Atypical forms of pre-excitation Other APs are postulated to result in cardiac pre-excitation. Atypical APs (also called Mahaim fibers) are connections between the right atrium or the AVN and the right ventricle, into or close to the right bundle branch.409414 Most of them are atriofascicular or nodoventricular (as initially described), but they can also be atriofascicular, atrioventricular, nodofascicular, or nodoventricular, depending on their variable proximal and distal insertions.413,414 Left-sided atypical pathways have also been described but are extremely rare.415417 Atypical pathways usually contain accessory nodal tissue, which results in decremental properties, and connect the atrium to the fascicles by crossing the lateral aspect of the tricuspid annulus, but posteroseptal locations can also be found in rare cases. Conduction is usually anterograde only, but concealed fibres have also been described.412,418 The following properties define the behaviour of atypical pathways: • Baseline normal QRS or different degrees of manifest preexcitation with LBBB morphology; • Programmed atrial pacing, leading to obvious manifest preexcitation following an increase in AV interval along with shortening of the HV interval at shorter pacing CLs;

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Figure 18 Atrioventricular re-entrant tachycardia. Left: othodromic atrioventricular re-entrant tachycardia due to a concealed posteroseptal accessory pathway. Retrograde P waves are negative during tachycardia in the inferior leads (arrows). Right: Antidromic atrioventricular re-entrant tachycardia due to an atriofascicular accessory pathway. The axis during tachycardia due to atypical pathways depends on the way of insertion into the right bundle and fusion over the left anterior fascicle. Downloaded from academic.oup.com/eurheartj/article/41/5/655/5556821 by guest on 07 October 2026