A case-control study was conducted in China to investigate the effect of 27.2 MHz radiofrequency electromagnetic fields on electrocardiograms of female workers operating radiofrequency machines at a shoe factory.
In the shoe factory, there were 80 radiofrequency welding machines operating at 8 kV in 30 out of 80 machines and 4 kV for the remaining machines. Measurements of the electric field strength were performed at 27 welding machines in the factory.
| Group | Description |
|---|---|
| Reference group 1 | control group: unexposed |
| Group 2 | exposed workers: 3 months - 2 years |
| Group 3 | exposed workers: > 2 years |
| Cases | Controls | |
|---|---|---|
| Eligible | 225 | 100 |
| Participants | 224 | 98 |
The 6 min electric field strength that the female workers were exposed to was 64.0 +/- 25.2 V/m (mean +/- standard deviation), which exceeded 61 V/m, the International Commission on Non-Ionizing Radiation Protection (ICNIRP) reference root mean square levels for occupational exposure. The mean exposure duration of the female workers was 22.8 +/- 17.8 months (mean +/- standard deviation).
18 workers (18.4%) had abnormal ECGs in the control group compared with 57 workers (25.4%) in the exposed groups; however, this difference was not statistically significant. Sinus arrhythmia was the most common observed change among the female workers (8.2% of the control group and 13.8% of exposed groups).
Although the exposure level to high frequency electromagnetic fields was high and steady, no statistically significant difference in heart rate, duration of the QRS wave, or QTc intervals were observed between the exposed groups and the control group.
The authors concluded that occupational exposure to 27.2 MHz radiofrequency radiation was not the cause of the ECG changes after considering the confounding factors.
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