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Mercury Exposure and Heart Rate Variability

pattismith

Senior Member
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3,932
Mercury Exposure and Heart Rate Variability: a Systematic Review

  • Matthew O. Gribble Alan Cheng Ronald D. Berger Lori Rosman Eliseo Guallar
    1. 1.Department of Preventive MedicineUniversity of Southern CaliforniaLos AngelesUSA
    2. 2.Division of CardiologyJohns Hopkins School of MedicineBaltimoreUSA
    3. 3.Welch Medical LibraryJohns Hopkins School of MedicineBaltimoreUSA
    4. 4.Department of EpidemiologyJohns Hopkins Bloomberg School of Public HealthBaltimoreUSA
    5. 5.Welch Center for Prevention, Epidemiology and Clinical ResearchJohns Hopkins Medical InstitutionsBaltimoreUSA
Metals and Health (A Barchowsky, Section Editor)
First Online: 26 June 2015

Abstract
Background
Mercury affects the nervous system and has been implicated in altering heart rhythm and function. We sought to better define its role in modulating heart rate variability, a well-known marker of cardiac autonomic function.

Design
This is a systematic review study.
Methods
We searched PubMed, Embase, TOXLINE, and DART databases without language restriction. We report findings as a qualitative systematic review because heterogeneity in study design and assessment of exposures and outcomes across studies, as well as other methodological limitations of the literature, precluded a quantitative meta-analysis.

Results
We identified 12 studies of mercury exposure and heart rate variability in human populations (ten studies involving primarily environmental methylmercury exposure and two studies involving occupational exposure to inorganic mercury) conducted in Japan, the Faroe Islands, Canada, Korea, French Polynesia, Finland, and Egypt.

The association of prenatal mercury exposure with lower high-frequency band scores (thought to reflect parasympathetic activity) in several studies, in particular the inverse association of cord blood mercury levels with the coefficient of variation of the R-R intervals and with low-frequency and high-frequency bands at 14 years of age in the Faroe Islands birth cohort study, suggests that early mercury exposure could have a long-lasting effect on cardiac parasympathetic activity. Studies with later environmental exposures to mercury in children or in adults were heterogeneous and did not show consistent associations.

Conclusions
The evidence was too limited to draw firm causal inferences. Additional research is needed to elucidate the effects of mercury on cardiac autonomic function, particularly as early-life exposures might have lasting impacts on cardiac parasympathetic function.

Heart Rate Variability:

"Heart rate variability is a widely used measure of cardiac autonomic function.
Most heart rate variability parameters fall into two common categories: time domain metrics, which describe beat-to-beat variation, and frequency domain measures, which examine the heartbeat pattern via spectral analysis [7]. The most common frequency domain measures are high frequency band (HF), often interpreted as a measure of parasympathetic activity, low frequency band (LF), often interpreted as a mixture of parasympathetic and sympathetic activity, and LF/HF ratio, often interpreted as a measure of sympathetic activity unless HF is reduced [7]. The specific biological interpretation of the heart rate variability parameters is open to some debate [8], but heart rate variability measures are generally regarded as reflecting cardiac autonomic nervous system functioning. Heart rate variability is a strong predictor of mortality after acute myocardial infarction [913], and may predict mortality after stroke [14] and ventricular tachyarrythmias [9]."

another extract on brainstem auditory evoked potentials :

"In the Faroe Islands’ cohort, cord blood mercury levels were associated with decreased CVRR, LF and HF band, although the associations were stronger at 14 years than at 7 years of follow-up. The inverse associations with LF and HF bands were interpreted as mercury-mediated decreases in sympathetic and parasympathetic modulation of heart rate variability.
In this cohort, mercury exposure was also associated with brainstem auditory evoked potentials, and the authors speculated that the effects of mercury on heart rate variability could reflect brainstem neurotoxicity of mercury."