Acute Ischemic Sinus Node Dysfunctions in Dogs

The effects of the occlusion of the two main atrial arteries irrigating the sinus node on sinus rhythm and postpacing sinus recovery were studied in 12 anesthetized dogs. Records of spontaneous rhythm and of postpacing sinus recovery were taken at control and hourly for 6 hours after the occlusion. The spontaneous cycle length (AA interval) was 335 ± 11 ms at control and 416 ± 17 ms (mean ± SE) (p < 0.005) one hour after the occlusion. It remained nearly unchanged during the following 5 hours of observation. The occlusion also shortened atrioventricular conduction time [AV interval] and reduced P‐wave amplitude in EGG lead II in 9 of these dogs. While the control postpacing sinus recovery time was 397 ± 13 ms, the 3‐hour value was 715 ± 165 ms. This prolongation persisted during the first four postocclusion hours but was Jess marked during the last two hours of observation. Moreover, the postpacing mode of return of the AA intervals to their prepacing value (sinus recovery pattern) became characteristically slow and progressive after occlusion, complete post‐pacing recovery often occurring only after 100 or more beats. Sequences of escape atrial and/or AV functional rhythms were frequently seen during this recovery. Atrial extrasystoles and short sequences of atrial tachycardias were observed in most dogs after occlusion. Conversely, none of these changes occurred during a 6‐hour experimental time in 5 control dogs in which the same protocol, occlusion excepted, was repeated. These observations show that the sinus node function in the dog is consistently affected by impairing its blood supply. Ischemic dysfunctions include sinus slowing, pacemaker shift, prolonged sinus recovery time, delayed post‐pacing recovery and supraventricular tachyarrhythmias.