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

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.To describe how the sinus node impulse originates, propagates, and collides in right and left atria with normal voltage.Fifty consecutive patients undergoing catheter ablation of atrial fibrillation with endocardial atrial voltage > 0.5 mV during high-density 3D-mapping were studied.Sinus node exits varied between 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 the systemic venous sinus in 6% of cases. Depending on these two key features of RA activation, interatrial conduction was mediated by the Bachmann bundle (64%) and posterior bundles (54%), with an overlap of the resulting LA breakthrough location. Wavefront collision was consistently observed at three sites: the septal aspect of the cavotricuspid isthmus; and the lower aspects of the dome and of the mitral isthmus.During sinus rhythm, atrial activation occurs via distinct sequences mediated by a complex interaction of anatomic factors.