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

Abstract

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. Sinkovec 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 other 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 A2H2 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 …