Arrhythmias in a hall of mirrors: Pediatric heterotaxy syndromes

Heterotaxy comes from the Greek words heteros, meaning “other than,” and taxis, meaning “arrangement.” It is thought to be caused by an embryological failure to differentiate along the right-left axis and can affect the thoracic and abdominal visceral organs. There are several different classification schemes that are beyond the scope of this commentary, but in short, they can be generally divided into “asplenia/polysplenia,” “right atrial isomerism/left atrial isomerism” based on morphology of the atrial appendages, and those that are not clearly mirror image reflections of the right and left sidedness, simply stated as “heterotaxy” or “indeterminate.” 1 Jacobs J.P. Anderson R.H. Weinberg P.M. et al. The nomenclature, definition and classification of cardiac structures in the setting of heterotaxy. Cardiol Young. 2007; 17: 1-28 Crossref PubMed Scopus (7) Google Scholar While it is not as simple as a duplication or mirror image of the right or left atria, the terminology is based more on the appearance of the appendages, yet the terms right/left atrial isomerism is often used for brevity even if not entirely anatomically accurate. These congenital failures of laterality often include complex congenital heart defects including unique structural and electrical abnormalities. The electrophysiological manifestations of heterotaxy syndromes can affect all levels of the conduction system, include sinus and atrioventricular (AV) nodes as well as atrial and ventricular tachyarrhythmias. In general (although there are always exceptions to the rules), those patients with right atrial isomerism tend to have duplicated sinus and AV nodes, leading to a propensity to supraventricular tachycardias including twin AV node tachycardia, whereas those with left atrial isomerism may be lacking the normal sinus and/or AV nodal tissue, leading to a propensity to sinus node dysfunction and/or AV block. 2 Ozawa Y. Asakai H. Shiraga K. et al. Cardiac rhythm disturbances in heterotaxy syndrome. Pediatr Cardiol. 2019; 40: 909-913 Crossref PubMed Scopus (10) Google Scholar Many patients with heterotaxy syndrome require complex cardiac surgical repairs, which can also predispose to postoperative arrhythmias and conduction abnormalities. 3 Marathe S.P. Zannino D. Cao J.Y. et al. Heterotaxy is not a risk factor for adverse long-term outcomes after Fontan completion. Ann Thorac Surg. 2020; 110: 646-653 Abstract Full Text Full Text PDF PubMed Scopus (7) Google Scholar Twin atrioventricular nodes, arrhythmias, and survival in pediatric and adult patients with heterotaxy syndromeHeart RhythmVol. 18Issue 4PreviewHeterotaxy syndrome is likely to involve arrhythmias from associated conduction system abnormalities, which are distinct in different subtypes of isomerism and may change further after interventions and remodeling. Full-Text PDF