COMPARISON OF ARRHYTHMOGENICITY OF ATRIAL-PACING AT SEVERAL RIGHT ATRIAL-PACING SITES - EVALUATION OF CANINE ATRIAL ELECTROGRAMS DURING ATRIAL-PACING AND ARRHYTHMOGENICITY FOR ATRIAL-FIBRILLATION

The changes in the duration of atrial electrograms and the appearance of AF during atrial pacing were compared among five atrial pacing site s in dogs to clarify the arrhythmogenicity of atrial pacing at differe nt atrial pacing sites. In seven mongrel dogs (15-20 kg), the right at rial surface was exposed by right thoracotomy. Atrial electrograms wer e recorded via bipolar electrodes with an interelectrode distance of 1 .2 mm at four right atrial sites: (1) the high right atrium (HRA), (2) the mid-right atrium (MRA), (3) the low right atrium (LRA), and (4) t he center of the pectinate muscle (PM). The duration of the atrial ele ctrograms at these four recording sites were measured during atrial pa cing with fixed cycle lengths of 200, 150, and 120 ms delivered at fiv e atrial sites: (1) the HRA, (2) the inferior vena cava (IVC), (3) the right atrial appendage (RAA), (4) Bachman's bundle (BB), and (5) the atrial septum (AS). In each dog, the atrial pacing with the 120-ms cyc le length was performed five times at each pacing site to evaluate the inducibility of AF. When AF was induced, the atrial recording site wh ich first showed a fragmented atrial electrogram was considered the in itiation site of the AF. AF was induced during 9 of 35 episodes of atr ial pacing at the HRA site, 3 1 of 35 at the IVC site, 5 of 35 af the RAA site, 3 of 35 at the BE site, and none at the AS site. The initiat ion site of AF was in the HRA site in 11 of 28 episodes of induced AF, in the MRA site in 9 of 28, and in the LRA site in 8 of 28. At each r ecording site, the shorter the paced cycle length, the longer the dura tion of the atrial electrogram regardless of the pacing site. During t he atrial pacing with the 200-ms cycle length, the HRA pacing resulted in the shortest duration of the atrial electrogram at each recording site in comparison with the other pacing sites. However, during atrial pacing at the two shorter paced cycle lengths, the duration of the at rial electrogram was shorter during the pacing at the BE or AS sites i n comparison with the other three pacing sites, i.e., the HRA, IVC, an d RAA sites. These results were the same for all atrial recording site s, but the prolongation of the atrial electrogram was most prominent a t the HRA and MRA recording sites, which are most likely initiation si tes of the induced AF. In the canine atria, (1) the initiation sites o f AF were likely to be the HRA, MRA, or LRA sites in comparison with t he PM site; and (2) the atrial pacing at the BE or AS sites was consid ered less arrhythmogenic for AF than the pacing at the HRA, LRA, or RA A sites.