ECG Changes in Humans Exposed to 50Hz Magnetic Fields: Srdjan S. BORJANOVIC, et al. Institute of Occupational Health "Dr. Dragomir Karajovic", Serbia and Montenegro-Possible health issues of ELF EMFs include cardiovascular effects since both electrocardiogram and heart-rate changes have been reported in the literature. A non-linear relationship between field strength and biological response has been reported in some studies. In this study, a total of 59 subjects, divided into three independent magnetic field strength groups, were compared. A calculated 12-hour time weighted average (TWA) value of the fields was used as an exposure metric for each of the three locations ("low": 0.067 µT, "medium": 1.18 µT and "high": 5.2 µT) and subsequently used to estimate workers' exposure at these sites. Electrocardiograms were recorded in the resting position. Five parameters were derived from the ECG: heart rate (HR), duration of P wave and QRS wave, and duration of PR and QT intervals. The QT intervals were normalized to a heart rate of 60 (QTc). The obtained data were analyzed first by means of multivariate analysis of covariance and then oneway univariate analyses of covariances (ANCOVA) using exposure duration as a covariate. Only the ANCOVA on the QTc interval was significant. Our results suggest that the relationship between field strength and response is non-linear: the adjusted mean QTc values are similar between the "low" and the "high" group, but significantly lower in the "medium" group. One possible interpretation of our results is that a specific exposure pattern might be responsible for the non-linear effects observed, so that generally, characterizing exposure to electric and magnetic fields using simple metrics such as TWA may be insufficient. Among the possible health effects of exposure to extremely low frequency electromagnetic fields (ELF EMFs), cardiovascular effects have been reported in the database of EMF bioeffects. Studies of ELF EMFs and the cardiovascular system have generally focused on acute rather then long-term effects. Both electrocardiogram (ECG) changes and heart-rate changes have been reported in the literature. An increase in the amplitude of the Twave signal in the rat electrocardiogram was observed during exposure to magnetic fields. This change, however, was the result of a superimposed electrical potential generated by aortic blood flow in the presence of the magnetic field 1) . The T-wave was affected rather than other components of ECG, since blood flows through the aorta during the period when ventricular repolarization is taking place. The increased T-wave voltage was unrelated to the electrical activity of the pacemaker area of the heart and the ECG change was simply a reflection of the coincident "magnetohydrodynamic" voltage generated by the blood flow in the presence of the applied magnetic field.Investigators at one laboratory (Midwest Research Institute, Kansas City, Missouri., USA) have studied the effects of EMFs on the heart rate in humans for several years 1,2...

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