Cardiac arrhythmias in the conscious dog after excision of the sinoatrial node and crista terminalis.

Abstract

A stable junctional rhythm was produced in 16 dogs after surgical excision of the sinoatrial node and a large section of the crista terminalis. An unstable ectopic atrial rhythm appeared within the 1st wk after surgery in 94% of the dogs. The pacemaker instability was characterized by spontaneous pacemaker shifts and periodic episodes of asystole which were prominent for several mo. after surgery in most of the dogs. In contrast to sinus arrhythmia observed before surgery, the ectopic atrial arrhythmias were not related to the respiratory cycle. The prompt disappearance of the asystoles after atropine or during treadmill exercise indicated the essential role of the vagus in producing the unstable rhythms. Atropine increased the average rate of the ectopic rhythms from 63 .+-. 3 heats/min to 107 .+-. 9 beats/min (P < 0.001) and shortened the corrected recovery time (CRT) following overdrive pacing from 3.8 .+-. 0.3 seconds to 1.9 .+-. 0.6 s (P < 0.001). Propranolol, in the absence of atropine, decreased the spontaneous heart rate from 56 .+-. 5 beats/min to 39 .+-. 6 beats/min (P < 0.01), and increased the CRT to 6.5 .+-. 2 s (P < 0.001) when administered after atropine. Unstable ectopic atrial pacemakers could possibly be responsible for some of the arrhythmias associated with the sick sinus syndrome in man.