Aim:

To evaluate alterations in hear rate variability (HRV), repolarization, and cardiac rhythms in medical residents working night shifts in Medellin, Colombia, by using Holter monitoring as an indirect, non-invasive measure of autonomic tone.

Material and methods:

This was a descriptive, observational study, in which 48-hour Holter monitoring parameters were evaluated and compared in medical residents before, during, and after working night shifts. Data were analysed in four 12-hour periods: period 1: night before night shift or 24 to 12 hours before night shift initiation; period 2: day of night shift (12 hours before night shift initiation); period 3: during night shift work (12 shift hours); and period 4: 12 hours post-shift. A total of 52 residents of clinical and surgical residency programs were included in this study. Mean age was 28 years, 59.6% were female, and 77% were enrolled in public universities. At total of 45 hours of Holter monitoring data per resident were recorded and analysed. Heart rate variability decreased significantly (p < 0.0001) during period 2 (day of night shift), with an additional -yet less pronounced- decrease during period 3 (night shift work).

Conclusions:

Medical residents working the night shifts exhibited a decrease in HRV during periods 2 (before shift) and 3 (during shift), being more evident during period 2 (anticipatory phenomenon). This change in HRV is due to decreased in parasympathetic activity, however remaining within the normal range. Future additional studies are required in order to determine the long-term effects of HRV variation.

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