Unravelling the Mysteries of the Human AV Node

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Dear Sir,

I read with great interest the elegant review written by Dr Efimov and colleagues on the structure and properties of the atrioventricular (AV) node in the last issue of this journal (AER 6(4):179–85).1 However, there are several points that need further clarification.

The authors state that total protein and mRNA levels of Cx40, Cx43 and/or Cx45 can be assessed qualitatively and quantitatively. However, representative immunolabelled sections are shown only for Cx43. From this, as well as other publications by the same team,2,3 I am left with the impression that genotyping data have only been presented for Cx43. However, Cx43 is one of four connexins that have been described to date (Cx40, Cx43, Cx45 and Cx30). Why do no data exist for them, and what is the impact of this lack of information on the characterisation of AV nodal properties? Is it just technically not feasible to obtain this information or is it just a matter of conventional priorities? I do believe that such genotyping is important for the full characterisation of the properties of the AV node and, perhaps, the unravelling of the mysteries of the circuit of AV nodal re-entrant tachycardia.4,5

Maria Kokladi, Department of Cardiology, Athens Euroclinic, Greece


  1. George SA, Faye NR, Murillo-Berlioz A, et al. At the atrioventricular crossroads: dual pathway electrophysiology in the atrioventricular node and its underlying heterogeneities. Arrhythm Electrophysiol Rev 2017;6(4):179–85.
    Crossref | PubMed
  2. Hucker WJ, McCain ML, Laughner JI, et al. Connexin 43 expression delineates two discrete pathways in the human atrioventricular junction. Anat Rec (Hoboken) 2008;291:204–15.
    Crossref | PubMed
  3. Hucker WJ, Sharma V, Nikolski VP, Efimov IR. Atrioventricular conduction with and without AV nodal delay: two pathways to the bundle of His in the rabbit heart. Am J Physiol Heart Circ Physiol 2007;293:H1122–30.
    Crossref | PubMed
  4. Katritsis DG, Marine JE, Latchamsetty R, et al. Coexistent types of atrioventricular nodal re-entrant tachycardia: implications for the tachycardia circuit. Circ Arrhythm Electrophysiol 2015;8:1189–93.
    Crossref | PubMed
  5. Katritsis DG, Marine JE, Contreras FM, et al. Catheter ablation of atypical atrioventricular nodal reentrant tachycardia. Circulation 2016;134:1655–63.
    Crossref | PubMed