Sinus node exit, crista terminalis conduction, interatrial connection, and wavefront collision: Key features of human atrial activation in sinus rhythm

Background: An understanding of normal atrial activation during sinus rhythm can inform catheter ablation strategies to avoid deleterious impacts of ablation lesions on atrial conduction and mechanics.

Objective: The purpose of this study was to describe how the sinus node impulse originates, propagates, and collides in right and left atria with normal voltage.

Methods: Fifty consecutive patients undergoing catheter ablation of atrial fibrillation with endocardial atrial voltage >0.5 mV during high-density 3-dimensional mapping were studied.

Results: Sinus node exits varied among patients along a lateral oblique arc extending from the anterior aspect of the superior vena cava (SVC) to the mid-posterior wall of the right atrium (RA). Conduction slowing or block at one of the smooth components that faces the crista terminalis was observed in 54% of cases, including complete block at the SVC musculature and systemic venous sinus in 6% of cases. Depending on these 2 key features of RA activation, interatrial conduction was mediated by the Bachmann bundle (64%) and posterior bundles (54%), with an overlap of the resulting left atrial breakthrough location. Wavefront collision was consistently observed at 3 sites: the septal aspect of the cavotricuspid isthmus, and the lower aspects of the dome and of the mitral isthmus.

Conclusion: During sinus rhythm, atrial activation occurs via distinct sequences mediated by a complex interaction of anatomic factors.