Distribution of Conduction Disorders in Patients With Congenital Heart Disease and Right Atrial Volume Overload

Houck CA, Lanters EA, Heida A, et al. JACC Clin Electrophysiol. 2020 May;6(5):537-548. doi: 10.1016/j.jacep.2019.12.009 PMID: 32439038

 

Take Home Points:

 

  • Patients with long-standing left-to-right shunts related to atrial septal defects (ASD) have significant regions of conduction delay and block in both atria and Bachman’s bundle
  • Conduction delay and block are seen most frequently in the right atrium, esp. the inter-caval region followed by Bachman’s bundle
  • Conduction block in Bachman’s bundle is associated with increasing left atrial size and a history of atrial fibrillation

 

 

 
Commentary by Dr. Jeremy Moore (Los Angeles) Congenital and Pediatric Cardiac EP section editor:  This intra-operative study sought to determine the atrial conduction characteristics among 31 ASD patients (secundum 58%, sinus venosus 36%, PAPVR 7%) with long-standing left-right shunts. High resolution epicardial mapping using a 128-electrode array (spacing 2 mm) of right atrial myocardium, Bachman’s bundle and left atrium was performed before commencing on cardiopulmonary bypass. Overall, the authors found conduction delay in 2.9% and conduction block in 1.9% of the areas studied.

 

Conduction delay and block were most commonly seen in Bachman’s bundle and right atrium, and less commonly in the pulmonary vein region and left AV groove, although the location of both delay and block were highly variable from patient to patient. Although the right atrium was the location of the shortest lines of conduction delay (typically patch) it was also the location of the longest lines of conduction block. Further assessment of the RA revealed a predilection for conduction disorders in the inter-caval region of the right atrium. Conduction block in Bachman’s bundle was associated with increasing LA size and secundum versus sinus venosus ASDs. For patients with AF, the only difference in prevalence of conduction disorder was found in Bachman’s bundle.

 

The authors noted that even though the effect of long-standing ASD volume overload tends to be right atrial enlargement, conduction disorders are not exclusively situated in the right atrium but also in Bachman’s bundle and to a lesser extent within the left atrium. The authors hypothesize that conduction block in Bachman’s bundle results in a propensity to AF due to the facilitation of micro-reentrant circuits. On the other hand, more severe conduction disorders in the right atrium, especially in the inter-caval region, could predispose these same patients to atrial flutter. The results hypothesis-generating and of substantial relevance to congenital electrophysiology.

 

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