Electrocardiogram of young diabetic subjects.

Standard 12-lead electrocardiogram patterns were studied in 100 Type I diabetic subjects aged 15-40 years and in 100 control subjects of the same age. Neither study group had evidence of clinical ischaemic heart disease or other systemic diseases which might affect cardiac function. The diabetic subjects had higher heart rates, lower electrocardiographic voltages and more T wave inversions than the controls. The diabetic women had longer QT intervals corrected for heart rate than the control women. The R-R interval variability (mean +/- S.D.) in the ECG was smaller in the diabetic subjects than in the controls (13 +/- 11 vs. 17 +/- 11%, p less than 0.05). Its magnitude was related to the heart rate variation in deep breathing, a measure of autonomic nervous function (r = 0.54, n = 50). The diabetic subjects with vagal autonomic neuropathy had an R-R interval variability of only 0-6%. The standard electrocardiograms of young asymptomatic diabetic subjects appear to differ in many respects from the those of healthy subjects in the same age group. The differences may reflect the presence of preclinical diabetic cardiovascular complications at an early age. A small or absent R-R interval variability helps to select patients for closer evaluation of autonomic function.