Article Text

Download PDFPDF
ECG phenomena: alternating QRS morphologies
  1. Christian Paech,
  2. Nicole Pfeil,
  3. Roman Antonin Gebauer
  1. Department for Pediatric Cardiology, University of Leipzig—Heart Center, Leipzig, Germany
  1. Correspondence to Dr Christian Paech, Department for Pediatric Cardiology, University of Leipzig—Heart Center, Strümpellstr. 39, Leipzig 04289, Germany, christian.paech{at}

Statistics from

A male newborn was referred to our centre for surgery of a hypoplastic left heart syndrome with atresia of the aortic and mitral valve. He received modified Norwood I procedure with patch reconstruction of the aortic arch and pulmonary artery bifurcation as well as implantation of a conduit between RV and pulmonary artery. Postoperative echocardiography showed good ventricular function and no signs of ventricular dyssynchrony.


What is the cause of the two different QRS morphologies? (figure 1)

  1. Pre-excitation

  2. Intermittent bundle branch block (BBB)

  3. Artefact

  4. Twin atrioventricular nodes

  5. Accelerated ventricular rhythm


From question on page XXX


The correct answer is twin atrioventricular nodes (AVNs). First reported by Mönckeberg in 1993, twin AVNs are an anatomic variant reported in various types of congenital heart disease.1 Twin AVNs may occur as completely isolated penetrating structures with independent connection to the His-Purkinje system or as sling (figure 2).2 Atrial activation may conduct to the ventricular specialised conduction tissue via both AVNs. This facilitates different QRS morphologies depending on which AVN conducts preferentially. Because only specialised conduction tissue is involved, QRS complexes are always narrow. The PR interval in twin AVNs should be normal, as both AVNs consist of healthy tissue. ECG characteristics include two discrete QRS morphologies in absence of ventricular pre-excitation pattern in 12-lead and 24-h ECG.3 Epstein (2001) added electrophysiologic criteria with an associated His-bundle electrogram per AVN; decremental and adenosine-sensitive conduction and inducible atrioventricular nodal reentrant tachycardia.4

Figure 2

Scheme depicting the different anatomic variants of twin atrioventricular nodes (AVNs) (arrows). The heart is shown in an anterior posterior projection. The anterior walls of the right atrium and RV are removed to demonstrate the intracardiac course of the specialised cardiac conduction system. (A) Two distinct AVNs and penetrating bundles result in two entirely separated cardiac conduction systems. (B) Two distinct AVNs and penetrating bundles with a distal connection. (C) Two distinct AVNs with a common penetrating bundle that is connected to a common distal conduction system.4 Electrophysiology study is needed to differentiate between these variants. RA, right atrium; RVOT, right ventricular outflow tract.

Neither BBB nor pre-excitation is present in this case. Absent pre-excitation is indicated by q-waves and a normal PR interval. Absent BBB is indicated as there is no significant widening of the QRS complex and the typical right axis deviation or left axis deviation in the frontal leads is not present. An accelerated ventricular rhythm is not likely, as there is a regular AV association and both QRS morphologies were present even at higher heart rates in 24 h ECG.

Conclusion: Twin AVNs are a rare anatomic variant. ECG features two discrete, narrow QRS complex morphologies in absence of a pre-excitation pattern. They may present as a coincidental finding or a substrate for reciprocating tachycardia.


View Abstract


  • Contributors CP: concept and drafting of the manuscript. NP: illustrations and critical revision. RAG: critical revision and approval of the manuscript.

  • Competing interests None.

  • Patient consent Obtained.

  • Provenance and peer review Not commissioned; internally peer reviewed.

Request Permissions

If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.

Linked Articles