Influence of the earliest right atrial activation site and its proximity to interatrial connections on P-wave morphology

P-wave morphology correlates with the risk for atrial fibrillation (AF). Left atrial (LA) enlargement could explain both the higher risk for AF and higher P-wave terminal force (PTF) in lead V₁. However, PTF-V₁ has been shown to correlate poorly with LA size. We hypothesize that PTF-V₁ is also affected by the earliest activated site (EAS) in the right atrium and its proximity to inter-atrial connections (IAC), which both show tremendous variability.

Atrial excitation was triggered from seven different EAS in a cohort of eight anatomically personalized computational models. The posterior IACs were non-conductive in a second set of simulations. Body surface ECGs were computed and separated by left and right atrial contributions. Mid-septal EAS yielded the highest PTF-V₁. More anterior/superior and more inferior EAS yielded lower absolute PTF-V₁ values deviating by a factor of up to 2.0 for adjacent EAS. Earliest right-to-left activation was conducted via Bachmann's Bundle (BB) for anterior/superior EAS and shifted towards posterior IACs for more inferior EAS. Non-conducting posterior IACs increased PTF-V₁ by up to 150% compared to intact posterior IACs for inferior EAS. LA contribution to the P-wave integral was 24% on average.

The electrical contributor's site of earliest activation and intactness of posterior IACs affect PTF-V₁ significantly by changing LA breakthrough sites independent from LA size. This should be considered for interpretation of electrocardiographical signs of LA abnormality and LA enlargement.