| Summary: | 碩士 === 高雄醫學大學 === 職業安全衛生研究所 === 98 === Background
Lead has been widely used in human lives and activities for millenniums in history. Its toxicity was not well known until reports in recent centuries. Ingestion of lead paint derivatives and inhalation of exhaust of vehicles using leaded gasoline are common exposure routes for all population in recent decades. Occupational lead exposure is still a main concern in industrial health though efforts have been made to reduce the emission of lead during the work process. Acute lead exposure has been reported to affect cardiac function and chronic exposure has been linked to atherosclerosis and increased cardiovascular mortality. Previous studies showed positive association between lead exposure and blood pressure, blood lipids, and increased left ventricular mass. However, there has been little research on the association of lead exposure and electrocardiographic abnormalities. One study using database from Normative Aging Study reported that, even at low exposures, an elevated bone lead level was positively associated with an increased risk of prolonged QT and QRS interval; however, blood lead level was not associated with ECG changes.
Purpose
The main purpose of this study was to examine the association of lead exposure with cardiac conduction disturbance among lead-exposed workers and general population in Taiwan. We would also like to determine the influencing factors of this effect evaluated by electrocardiography.
Methods
The participants comprised 312 lead workers from a lead-acid battery factory and 329 referents who had no known occupational exposure to lead. During their annual health examination they were invited to take part in the survey. Demographics, medical history, work exposure history, alcohol and tobacco consumption, were collected by self-administered questionnaire. Blood lead levels were measured by graphite furnace atomic absorption spectrometry. Standard resting 12-lead electrocardiograms were obtained and the ECG features studied were heart rate, PR interval, QRS interval, and QT interval.
Results
The mean blood lead level was 26.05 ± 13.98μg/dl and 2.62 ± 1.42μg/dl in lead-exposed group and reference group respectively. The lead workers had significantly lower systolic blood pressure, fasting plasma glucose, triglyceride, and LDL-cholesterol level. Compared to the referents, lead workers had significantly shorter PR interval (p=0.032) and longer heart rate-corrected QT interval (p<0.001). For heart rate-corrected QRS intervals there were no difference between lead-exposed group and reference group; however, the lead workers had significantly higher percentage of prolonged QRSc (p=0.011). Among all participants, a 1μg/dl increase in blood lead level was significantly associated with an increase in heart rate-corrected QT interval of 0.212 ms (p= 0.002) after adjusting for age, gender, BMI, and other potential confounders. Compared to female, male has longer PR interval (β= 5.817, p= 0.014) , shorter QRSc interval (β= -3.918, p= 0.015), and shorter QTc interval (β= -20.812, p<0.001). Older participants had longer time interval of ventricular depolarization and repolarization (QTc interval) with an increase of 0.442 ms per year (p< 0.001). Participants with higher BMI (β= 0.476, p= 0.02) and higher systolic blood pressure (β= 0.164, p= 0.009) had longer duration of ventricular activation (QRSc interval). Systolic blood pressure was significantly associated with QTc interval (β= 0.187, p= 0.045). Drinking habit seemed to increase QTc interval though the significance level was relatively low (β= 8.961, p= 0.043). Diastolic blood pressure and smoking habit were not related to these three ECG parameters.
Conclusion
The data suggest that lead exposure is positively associated with prolonged QTc interval even when gender, age , systolic blood pressure and alcohol consumption may also have an effect on ventricular reploarization.
Keywords: lead, QT interval, cardiac conduction
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