Low and nonrhythmic heart rate of the mole rat (Spalax ehrenbergi): Control by the autonomic nervous system

Summary ECG of mole rats (Spalax ehrenbergi) was recorded by chronically implanted electrodes. The average heart rate of unrestrained, resting animals (mean body mass 191 g±35 S.D.) in normoxia and at room temperature is 152 beats/min±42 S.D. It is nonrhythmic and about one third of the rate expected for an animal of this mass. ECG revealed that each heart beat is normal. From atropine and propranolol administration, it was evident that the low heart rate results from : (a) low intrinsic heart rate (285 b/min±30 S.D.), (b) high parasympathetic tone (51%±12 S.D.) and (c) low sympathetic tone (3.6%±1.6 S.D.). Unilateral vagotomy showed that the degree of left or right vagus dominancy in the mole rat differs in each individual: it may even reach a complete left vagus control, in contrast to other mammals where right vagus dominancy is apparent.