Characteristics of right atrial activation during coronary sinus pacing

Introduction: Anatomic and electrical connections between the left atrium and right atrium (RA) have been described. The relationship between coronary sinus (CS) pacing site and RA activation has not been examined.Methods and Results: Fifteen anesthetized swine underwent high-density noncontact mapping of the RA during pacing from up to five different sites within the CS. Isopotential mapping identified the site of earliest RA depolarization and the pattern of subsequent activation. Hearts were excised and endocardial dissection performed. Earliest RA activation occurred at the CS os with proximal CS pacing sites and at Bachmann's bundle at distal pacing sites. The mean depth at which a shift in earliest RA activation site occurred was 46 ± 13 mm (range 21 to 63 mm). RA activation times following earliest activation at the CS and Bachmann's bundle were 40 ± 4 msec and 51 ± 6 msec (P < 0.002). Conduction delay or block was recorded at the lateral cavotricuspid isthmus, terminal crest, and tendon of Todaro. Latest RA activation always occurred in the high anterolateral atrium after ascending the anterolateral wall. The lateral RA was activated by the wavefront that traversed the posterior wall rather than by the wavefront crossing the cavotricuspid isthmus, even with earliest RA activation at the CS os.Conclusion: The site of earliest RA activation during CS pacing is dependent upon the pacing depth within the CS. In the porcine heart, areas of conduction delay influence RA activation patterns and timings. These findings may have implications for patients undergoing assessment of radiofrequency ablation of atrial flutter