Indexes of cardiac autonomic profile detected with short term Holter ECG in health care shift workers: a cross sectional study.

BACKGROUND: The assessment of early effect of shift work-related circadian rhythms desynchronization and work-related stress in health care workers has gained a primary role among the duties of the occupational physician. OBJECTIVES: Aim of our study was to assess the cardiac autonomic modulation through quantification of sinus rhythm variability, as an index of the adaptability to shift work of the cardiovascular system in healthcare shift workers. METHODS: We measured Heart Rate Variability (HRV) by short-term (60 minutes) Holter Electrocardiography (ECG) during the regular duties in the respective department of 42 healthcare workers (31 nurses and 11 physicians) of an Italian Hospital (12 male and 30 females, aged 24-58 years), working on 3 shifts with a forward fast rotation with rest at the end of the night shift (7 am - 2 pm; 2 pm - 10 pm; 10 pm - 7 am) or in a fixed daytime shift (8 am - 2 pm). Measurements were all performed between 9 am and 12 am for fixed day workers and between 9 am and 12 pm or between 10 pm and 1 am for shift workers. The following HRV parameters were compared between the subgroups of shift workers and daytime workers: mean heart rate (HR), standard deviation of all normal RR (NN) intervals (SDNN), standard deviation of the averages of NN intervals in all 5-minute segments of a recording (SDaNN) and the triangular index (the integral of the density distribution divided by the maximum of the density distribution). We used parametric tests for independent series to compare HRV parameters by subgroups within the study subjects. We also tested correlation between the variables of interest and the association between HRV and shift work modality, along with other covariates, by means of a multiple linear regression analysis. RESULTS: We found significantly lower values of SDaNN in shift workers compared with workers engaged solely on day shifts (50.80 ms vs 66.71 ms; p=0,014). The mean heart rate did not show any significant difference between day workers and shift workers (85.78 bmp vs 85.53 bpm respectively). Multivariate analysis showed a significant association between SDNN and female gender and age, while no significant associations were found between HRV and shift work. DISCUSSION: The autonomic control of the heart rhythm could be disrupted by desynchronization of the biological rhythm secondary to the organization of shift work and night work. Shift work is an important factor of social and biological distress, influencing the adaptability of the cardiovascular system to stimuli and demands of work organization.