Twenty-one normal subjects and 64 diabetics with varying severity of autonomic damage underwent 24-h ambulatory EKG monitoring. No diabetics had the “sick sinus syndrome,” and the frequency of arrhythmias was no higher than in the normal subjects. The diabetics had higher mean hourly heart rates, and with increasing autonomic damage there was reduction in diurnal heart rate variation. The mean waking and sleeping heart rates were higher in the diabetics. The maximum heart rates were not significantly different, but the minimum heart rates were significantly higher in the diabetics. These previously unrecognized abnormal 24-h heart rate patterns provide further evidence of damage to the heart rate-controlling mechanisms in diabetes mellitus.

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