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.......................................................................... Peri-mitral flutter, sometimes incorporating silent areas at the roof of the LA, is ablated in a similar way to peri-tricuspid circuits. However, the deployment of a stable line of block at critical isthmuses is more challenging.308310 Circuits around the PVs are also frequently recognized and ablated.280,295,296 Intervention to treat these tachycardias after the initial procedure should be delayed, if possible, for >_3 months. As part of the maturation process of the deployed lesions, some tachycardias may be transient in nature,311 and initial rate control and/or use of antiarrhythmic drugs is favoured.

11.2 Atrioventricular junctional

arrhythmias 11.2.1 Atrioventricular nodal re-entrant tachycardia AVNRT denotes re-entry in the area of the AVN, but the exact circuit remains elusive. The AVN is a three-dimensional structure with greater variability in the space constant of tissue, and poor gap junction connectivity due to differential expression of connexin isoforms, conditions that provide an explanation for dual conduction and nodal re-entrant arrhythmogenesis.312314 There has also been considerable histological and electrophysiological evidence that the right and left inferior extensions of the human AVN, and the atrionodal inputs that they facilitate, may provide the anatomical substrate for the slow pathway.315,316 Thus, comprehensive models of the tachycardia circuit for all forms of AVNRT based on the concept of atrionodal inputs have been proposed.47,317

Onset of AVNRT seems to occur bimodally over time. In many patients, attacks indeed manifest early in life, whereas in a substantial proportion of patients AVNRT starts later, e.g. in the fourth or fifth decade of life.318 One-half of the patients with minimal symptoms and short-lived, infrequent episodes of tachycardia may become asymptomatic within the next 13 years.319 AVNRT may result in AF that usually, although not invariably, is eliminated following catheter ablation of AVNRT.320 Familial AVNRT should be considered.321

11.2.1.1 Diagnosis

11.2.1.1.1 12 lead electrocardiogram during tachycardia. Typically, AVNRT is a narrow complex tachycardia, i.e. QRS duration <120 ms, unless there is aberrant conduction, which is usually of the RBBB type, or a previous conduction defect exists (Figure 13). AV dissociation is exceptionally uncommon, but it can occur as neither the atria nor the ventricles are necessary for the re-entry circuit. Thus, coexistence with AF or AV conduction block is possible but rare.66,322 ST-segment depression may be seen during or after the tachycardia. In the typical form of AVNRT (also called slowfast AVNRT), retrograde P waves are constantly related to the QRS and, in the

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Figure 13 Atrioventricular nodal re-entrant tachycardia. (A) Typical atrioventricular nodal re-entrant tachycardia. (B) Atypical atrioventricular nodal reentrant tachycardia. (C) Atypical AVNRT with (unusual) left bundle branch block aberration. Retrograde P waves are indicated by arrows. Downloaded from academic.oup.com/eurheartj/article/41/5/655/5556821 by guest on 07 October 2026