RESPONSE OF TYPE-I ATRIAL-FIBRILLATION TO ATRIAL-PACING IN HUMANS

Background High-density mapping studies of atrial fibrillation (AE) ha ve suggested the presence of an excitable gap. The purpose of this stu dy was to assess the local and left atrial response to pacing at the h igh right atrium during type I AF in humans. Methods and Results Pacin g was performed at the high right atrium during type I AF in 24 patien ts in the electrophysiology laboratory. The response to pacing was ass essed at cycle lengths 10, 20, 30, 40, and 50 ms less than the mean ba seline atrial cycle length. Digitized tracings of the baseline tachyca rdia and the response to pacing were recorded from the high right atri um and from the distal coronary sinus. Computer analysis of these sign als was used to calculate a left atrial electrogram density before, du ring, and after pacing. Two hundred eighty-eight segments of AF with a duration of 3.9+/-0.5 seconds (mean+/-SD) were analyzed. Local captur e of the right atrium during AF was demonstrated for at least one paci ng cycle length in each patient. The left atrial electrogram density w as significantly greater than baseline at each pacing cycle length tha t resulted in local capture, except when pacing at 50 ms less than the mean AF cycle length. There was no significant change in the baseline left atrial electrogram density compared with baseline when pacing di d not result in local capture of AF. Conclusions Local right atrial ca pture is often possible by pacing during type I AF and consistently in fluences the left atrial electrograms recorded in the coronary sinus. These results confirm the presence of excitable tissue in the right an d left atria in type I AF.