Typical atrioventricular nodal re-entrant tachycardia: still many obscure points

P. Alboni, L. Gianfranchi
2011 Europace  
This editorial refers to 'Electrophysiology of anterograde right-atrial and left-atrial inputs to the atrioventricular node in patients with atrioventricular nodal re-entrant tachycardia' by M. Š inkovec et al., on page 869. Our knowledge of the re-entry circuit of typical atrioventricular nodal re-entrant tachycardia (AVNRT) is limited, mainly on account of the unfeasibility of recording AV nodal potentials during an electrophysiological study and the lack of adequate animal models, as for
more » ... r tachyarrhythmias. Early studies suggested that typical AVNRT was due to re-entry totally confined within the compact AV node as a result of functional dissociation between a fast pathway (FP) and a slow pathway (SP). This hypothesis was based on the observation that dual AV nodal physiology (jump ≥ 50 ms of A 2 H 2 interval) was usually present in patients with AVNRT and appeared to be infrequent in control subjects. This jump was interpreted as representing induction block in the anterograde FP with selective conduction through SP. More recent studies suggested that SP and FP involved in the re-entry circuit of typical AVNRT represented conduction through different atrionodal connections, the site of earliest atrial activation being different between retrograde conduction over FP and SP. In other words, these pathways represent atrionodal connections outside the compact AV node rather than longitudinal dissociation within the AV node. There is extensive experimental and clinical electrophysiological evidence that the anterograde SP has its anatomic substrate in the inferior extensions of the AV node, located in Koch's triangle, which appear to constitute a necessary limb of the tachycardia circuit. 1 There are two inferior extensions, one rightward and the other leftward, which are a direct continuation of the compact AV node; the rightward extension is much longer than the leftward one. 1 In the vast majority of patients, the rightward extension appears to be involved in the re-entry circuit of typical AVNRT. 1 The tachycardia circuit may occasionally involve the leftward extension, in which case a left-sided ablation procedure is needed. 2 During programmed atrial stimulation, multiple discontinuities in the AV node conduction curve (multiple jumps) can be observed in 5 -40% of patients with typical AVNRT. 3 This electrophysiological finding probably reflects the presence of multiple anterograde SPs, as demonstrated in animal studies. 2 However, in the majority of these patients, only one of the SPs appears to be involved in sustained tachycardia, though the involvement of up to three has been described. 2 The retrograde FP is even less understood than the anterograde SP. In almost all patients with typical AVNRT, the earliest retrograde atrial activation occurs anteriorly, in the apex of Koch's triangle, and is recorded in the His bundle electrogram. The anatomical substrate of the retrograde FP has not been defined. Superior atrial inputs exist, but histological analysis of a small number of explanted human hearts with documented dual pathway physiology did not show any difference from normal hearts; in particular, a definite atrio-His bundle was not found. 2 Superior atrionodal inputs consist of atrial myocardial cells that descend into the AV node and connect via a rim of transitional cells. 1 However, long experience in the electrophysiology laboratory suggests that the retrograde FP has 'Kent bundle-like' properties, at least in the vast majority of patients with typical AVNRT. Indeed, the HA (or VA) interval does not display (or displays only minimally) decremental conduction; it remains constant during atrial stimulation even if marked variations in A 2 H 2 duration are observed, during variations in AVNRT heart rate and during ventricular incremental pacing. Moreover, the HA interval does not change after administration of propranolol and atropine. 4 These data suggest that, in many patients, the anatomic substrate of the retrograde FP is constituted by muscle fibres with fast conduction and not by the nodal and transitional cells, which should show decremental conduction. Anselme et al. 5 performed simultaneous multisite catheter mapping of Koch's triangle during AVNRT and ventricular pacing at a similar cycle length. They found that during typical AVNRT, the earliest retrograde atrial activation was recorded near the apex of Koch's triangle in 90% of patients, confirming previous results. However, they have shown that the retrograde FP is heterogeneous within the area of Koch's triangle, both during
doi:10.1093/europace/eur031 pmid:21325344 fatcat:2txtnmrt55ekdnotrj3vo7eola