Mean 24 hour heart rate, minimal heart rate and pauses in healthy subjects 40–79 years of age

In order to establish normal limits for mean 24 h heart rate (⁠HR¯t and pauses, 24 h ambulatory ECG recordings from 260 healthy subjects 40–79 years of age were analysed. The HR¯24h varied from 53 to 95 beats/min (mean±2 s.d.: 74±I8 beats/min). The minimal HR¯t varied from 36 to 78 beats/min (mean± 2 s.d.: 56 ±16 beats/min). Analysis of variance showed an additive effect of smoking, sex, leisure-time physical activity and age on both HR¯t, and the effect of the three first factors was statistical significant at the 1% level for both heart rate variables. The males, the non-smokers and the physically active subjects had a lower HR¯24h and a lower minimal HR¯t than females, smokers and passive subjects. Older subjects had a lower HR¯t was non-significant. A total of 77 subjects (30%) had a pause (R-R interval≥1500 ms), but in only 12 (5%) did the pause exceed 1750 ms with the longest pause measuring 2040 ms. Further analysis of the longest pause in each of the 77 subjects with pauses showed that 46 of the longest pauses occurred at night following a gradual decrease in the R-R intervals for a few beats (‘post-acceleration pauses’). In 12 subjects the longest pause was caused by sinus arrest, and in nine cases a blocked atrial premature beat was thought to be present. Wenckebach A- V block was seen in only two subjects. It is concluded that sex, age, smoking and leisure-time physical activity are all factors that have to be considered for a thorough evaluation of heart rate variables in the 24 h ambulatory ECG.