P3799 - Experimental model of interatrial block by Bachmann bundle conduction block

Abstract

Background The recognition of advanced IAB is becoming an important clinical landmark due to its association with atrial fibrillation, the so-called Bayes' syndrome. The electrocardiographic (ECG) criteria of interatrial block (IAB) have been established. A P-wave duration ≥120 ms is considered partial IAB and if there is a biphasic P-wave in the inferior leads advanced IAB. The pathophysiology of this ECG finding has been largely discussed. IAB has been explained as the result of the retrograde activation of left atrium due to complete block in the Bachmann bundle (BB).

Purpose To assess the ECG changes resulting of blocking BB conduction in an experimental healthy animal model. Additionally, to compare the pattern of activation of the left atrium before and after the block.

Methods Six open-chest anesthetized healthy adult swine were studied. A twelve-lead ECG was continuously recorded. The BB was epicardially accessed at the traversus sinus of the pericardium. At that level, monopolar electrosurgical energy (3 animals) and radiofrequency energy (3 animals) (Boston Scientific Blazer™ II XP, 8 mm tip) was applied until extensive tissue disruption was present and permanent P-wave changes observed. An electroanatomical map CARTO® XP (Biosense Webster Inc) of the right and left atrium was performed in two animals before and after energy deployment. Finally, animals were sacrificed, and tissue samples collected for anatomopathological examination.

Results After energy application, all animals showed a significant prolongation of P-wave duration from 59±11 msec to 115±13 msec (p<0.001) with appearance of a biphasic P-wave pattern in the inferior leads. The CARTO® maps showed a change in left atrial activation, cranio-caudal at baseline and caudo-cranial at the end of the procedure. (Figure) The histological analysis showed transmural lesions at the level of the BB in all the specimens.

Conclusion IAB ECG pattern, accompanied by a marked change in the activation of the left atrium, develops after blocking the conduction at the level of the BB in an experimental healthy animal model. These results confirm the association of IAB and BB conduction block and suggest that IAB represents an independent entity.