Sinus Node Reentry

The phenomenon of sinus node reentry was investigated in 20 dogs by programed atrial stimulation during sinus rhythm and atrial pacing. Recordings were made simultaneously at multiple atrial sites. In 18 dogs, a closely coupled premature atrial beat (A 2 ) introduced into the region of the coronary sinus, the right or the left atrial appendage, or the Bachmann bundle was followed 100-300 msec later by an accelerated beat (A 3 ) consistent with sinus node reentry. The atrial activation sequence and the P-wave morphology of A 3 and of the spontaneous sinus beats were similar. The occurrence of A 3 during sinus rhythm and atrial pacing was dependent on the coupling interval of A 2 and the arrival time of excitation in the region of the sinus node but was independent of the atrial site at which A 2 was introduced; A 3 could be clearly distinguished from local or atrioventricular node reentry and sinus node entrance block. Moreover, crushing of the sinus node (10 dogs) or vagal stimulation (7 dogs) prevented the appearance of A 3 in all dogs, presumably by blocking the sinus node reentry pathway. During graded vagal stimulation a progressive increase in the A 2 -A 3 interval occurred. Sinus node reentry was sustained for three cycles in 1 dog. Sinus node reentry may be one mechanism for interpolated atrial premature depolarization and some atrial tachyarrhythmias seen clinically.