What is the clinical evidence from this study?

Study design: Cohort. Population: Cardiovascular-susceptible healthy nurses (n=26). Intervention: Prolonged high job strain vs. Stable low job strain. Primary outcome: SDNN (standard deviation of all normal RR intervals) on working days (p=0.02).

September 24, 2014International Journal of Occupational Medicine and Environmental Health43 citationsOpen Access

Prolonged job strain reduces time-domain heart rate variability on both working and resting days among cardiovascular-susceptible nurses

RBRossana Borchini MFMaurizio Ferrario LBLorenza Bertù

Key Result

Prolonged high job strain significantly reduced time-domain heart rate variability, specifically SDNN on working days, compared to stable low strain (128.9 ms vs 169.1 ms, p=0.02) among cardiovascular-susceptible nurses.

Study Design

Type

Cohort (n=26)

Multicenter

Structured PICO

Does prolonged job strain reduce time-domain heart rate variability in cardiovascular-susceptible nurses?

Population

26 healthy nurses with a family history of cardiovascular or metabolic disease underwent 24-hour ECG monitoring to evaluate the effect of prolonged job strain on heart rate variability.

Exposure

Prolonged high job strain (high strain in both surveys 1 year apart) or recent high job strain (high strain at second survey only).

Comparator

Stable low job strain (low strain in both surveys).

Outcome

Time-domain heart rate variability (HRV) metrics (SDNN, SDNN_Index, SDANN) on working days and resting days.surrogate

Persistent job strain lowers HRV time-domain parameters, suggesting autonomic nervous system dysregulation as a potential intermediate pathway between work stress and cardiovascular disease.

Main Result

Absolute Event Rate: 128.9% vs 169.1%

p-value: p=0.02

Limitations

Small sample size, in particular the small number of subjects in the recently strained group
Reduced statistical power which may be responsible for some borderline statistical significance
Results need to be replicated on larger samples

Abstract

INTRODUCTION: Modifications of hearth rate variability (HRV) constitute a marker of the autonomic nervous system (ANS) deregulation, a promising pathway linking job strain (JS) and cardiovascular diseases (CVD). The study objective is to assess whether exposures to recent and prolonged JS reduce time-domain HRV parameters on working days (WD) among CVD-susceptible nurses and whether the association also persists on resting days (RD). MATERIAL AND METHODS: 313 healthy nurses were investigated twice with one year interval to assess JS based on the demand-control and the effort-reward models. 36, 9 and 16 CVD-susceptible nurses were classified as low JS in both surveys (stable low strain - SLS), recent high JS (high JS at the second screening only-RHS) and prolonged high JS (high strain in both surveys-PHS), respectively. In 9, 7 and 10 of them, free from comorbidities/treatments interfering with HRV, two 24-h ECG recordings were performed on WD and RD. Differences in the time domain HRV metrics among JS categories were assessed using ANCOVA, adjusted for age and smoking. RESULTS: In the entire sample (mean age: 39 years, 83% females) the prevalence of high job strain was 38. 7% in the second survey. SDNN (standard deviation of all normal RR intervals) on WD significantly declined among JS categories (p = 0. 02), with geometric mean values of 169. 1, 145. 3 and 128. 9 ms in SLS, RHS, PHS, respectively. In the PHS group, SDNN remained lower on RD as compared to the low strain subjects (142. 4 vs. 171. 1 ms, p = 0. 02). Similar findings were found for the SDNNIndex, while SDANN (standard deviation of average RR intervals in all 5 min segments of registration) mean values reduced in the PHS group during WD only. CONCLUSIONS: Our findings suggest that persistent JS lowers HRV time-domain parameters, supporting the hypothesis that the ANS disorders may play an intermediate role in the relationship between work stress and CVD.

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