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Epidemiological evaluation of the coronary risk in physical laborers in nonferrous metallurgy. Part II: Coronary disease. [Epidemiologiczna ocena zagrozenia choroba wiencowa u pracownikow fizycznych przemyslta hutniczego metali niezelaznych. Czesc II: Choroba wiencowa.** Przegl Lek 1980;37(6):507-10.

L. Giec, A. Wnuk-Wojnar, M. Trusz-Gluza, A. Szulc, and W. Kargul*:

*First Cardiology Clinic of the Cardiology Institute of the Silesian Academy of Medicine in Katowice. Director Prof. Dr. Hab. Med. L. Giec. Authors' address: I Klinika Kardiologii SI. AM, ul. Ziolowa 4, 40-634 Katowice. [First Cardiology Clinic of the Cardiology Institute of the Silesian Academy of Medicine in Katowice, 4 Ziolowa St., 40-634 Katowice, Poland]

*Accepted December 19, 1979.

Translated from Polish by the Ralph McElroy Co., Custom Division P.O. Box 4828, Austin, Texas 78765 USA

Abstract

Analysis was performed in 1000 physical workers (900 males, 100 females) aged 21-60 years with the professional exposure to zinc, lead or cadmium. Angina of effort according to Rose was present in 14.1% of studied population. True and probable features of coronary heart disease were found respectively in 0.5 and 3.4% of resting electrocardiograms. The sub maximal exercise test revealed probable ischemia response in 10.1% of studied persons. It has been shown that coronary pain is more frequent in workers exposed to cadmium. However, either angina in history or positive exercise test were less frequent in the persons exposed to zinc.

ADDITIONAL KEY WORDS: angina of effort - electrocardiogram at rest - exercise test - zinc - lead - cadmium

Introduction

The results of clinical, epidemiological, and experimental animal studies indicate a correlation between an excess or deficiency of certain trace elements and the onset and development of coronary disease [2, 15, 19]. Most of these correlations have not been unambiguously explained or even proved.

We decided to evaluate the incidence of coronary disease in a population occupationally exposed to zinc, lead, and cadmium, looking for any correlation between the disease and exposure to these elements.

Materials and methods

A description of the observed population of 1000 physical laborers (900 men and 100 women), aged 21-60, in nonferrous metallurgy, and an outline of the plan of study were given in Part I [17]. The subjects were interviewed concerning the working environment and given a modified and expanded Rose questionnaire [13]. All the subjects were given a 12-lead resting electrocardiogram (EGG) with a three-channel Multicard apparatus. Subsequently, if there were no contraindications from the resting EGG recording or a medical examination, they were exercised on a cycloergometer with submaximal exercise (75-85%). Electrocardiograms were recorded during, immediately after, and 2.5 and 5 minutes after exercise. They were evaluated using a modified [13] Minnesota code.

An epidemiological diagnosis of definite, probable, or questionable coronary disease was made on the basis of criteria given by Askanas and Rywik [1].

In addition, all the workers were tested for serum concentrations of lead and zinc, and the lead, zinc, and cadmium concentrations in the air of their workplaces were measured [4, 11, 17]. The data were statistically processed using the chi square test on an Odra 1305 computer.

Results

A detailed analysis of the measurements of zinc, lead, and cadmium in the air of the workplace and in the serum was given in the previous article [17]. Concentrations above the maximum permitted [threshold limit] concentration for the air of the workplace were found in 74.3% of the workers for lead, 57.9% for zinc, and 7% for cadmium. It also turned out that the degree of exposure did not differ significantly in different age ranges.

There was a positive interview for first and second degree angina of effort in 14.1% of the patients, while in another 9.8% there was pain in the chest cavity which did not meet Rose's criteria [13]. Pain reminiscent of myocardial infarction was reported by 3.6% of the patients. The frequency of subjective symptoms of angina of effort rose with age in 19.3% of men in their fifties and 32.2% of women in their forties. Only 1.2% of the workers were found to have had a previous medical diagnosis of coronary heart disease, while 0.2% had been treated for myocardial infarction.

Table I shows the incidence of electrocardiographic signs of certain, probable, and questionable cardiac ischemia in resting and exercise electrocardiograms of the workers by age and sex. Definite or practical signs of previous myocardial infarction were found in the ECGs only in men over 40 years old. The incidence of other signs rose sharply with age. Signs of questionable ischemia in the resting EGG and of probable or questionable ischemia in the resolved postexercise EGG (sometimes twice) were more frequent in women, especially those in their forties and fifties, while probable electrocardiographic signs of coronary disease at rest were more frequent in men.

According to the criteria given by Askanas and Rywik [1], epidemiological suspicion of coronary disease was recorded when certain or probable signs were present (Table II) in the anamnesis and/or electrocardiogram. Coronary disease was suspected in up to 25% of the workers studied. A more definite basis for such a diagnosis was a positive EGG result together with a positive interview for angina of effort, with such confirmation in only 3% of the patients, while 4.9% of the subjects had both angina of effort and ECGs with questionable signs of ischemia.

Statistical analysis by the chi square method demonstrated a definite relation between the occurrence of signs of coronary disease and toxicological exposure in the work environment (Table III). In individuals exposed to zinc, signs of coronary disease were statistically significantly rarer in the anamnesis and electrocardiograms. Angina of effort was more often reported in workers exposed to cadmium, while electrocardiographic signs were less frequent in those exposed to lead.

Discussion of results

The incidence of suspected coronary disease in our population (25%) is much higher than that reported by other Polish authors [8, 10, 14, 16]. This is primarily because we used the additional diagnostic criterion of the exercise electrocardiogram. A positive interview for angina of effort was found in the studies of Sznajd et al. in 5-6% of those questioned [16]. In a similar age group (41-60), we obtained a positive interview in about 17% of the subjects. This confirmed the observation made for the populations of Sochaczew, Plocek, and Cracow [8, 10] that women more frequently reported subjective symptoms of angina of effort. In an epidemiological study [6], it was suggested that morbidity from coronary disease may actually be higher in women than in men. Our own experiments and those of the authors of [10], who carried out repeated studies of morbidity and susceptibility to coronary disease, lead us to seek the reason for the imperfections in the questionnaire recommended by the WHO [World Health Organization], which can give false positive results.

The incidence of certain and probable signs of coronary disease which we obtained in the resting EGG increases sharply with age and these signs are present mainly in men, as in the studies of Rywik et al. [14] and Wojcikiewicz et al. [18]. The use of submaximal exercise produced probable electrocardiographic signs of coronary disease in a large group of workers (10% of those studied). Only 5 persons in this group reported complaints qualified as coronary disease. Other authors [9, 12] describe a positive result for the exercise test in 3-13% of "symptomless" men. The diagnostic specificity of the exercise test in detecting cardiac insufficiency is variously evaluated in the literature [9, 12]. The frequency of false positive results ranges from 6-50%, depending on the choice of the group studied and the type of verification of the diagnosis (clinical or angiographic). This method is rather questionable in studying clinically healthy persons [12], in whom coronarography can demonstrate significant narrowing of the arteries in no more than 40-50% of cases with a positive exercise test. However, isolated observations of persons with significant stress-related ST depression indicate a much higher incidence of myocardial infarction, sudden coronary death, and other symptoms of coronary disease in these persons [5]. The fact that we very rarely had a positive result for the exercise test in young men and a much higher incidence in persons over 40 is definite evidence that ECG changes of types IV1, V1,2, and VII1 (according to the Minnesota code) may be ischemic in nature. Signs of questionable ischemia or less specific ST-T deviations occurred after exercise significantly more frequently, even in young persons.

In the population which we studied, the group of women was small. Many of them had more or less pronounced irregularities in the electrocardiogram, primarily after exercise. Gumming [3], in exercise studies of 357 healthy women, showed that there were ST-T changes in 25-60%, depending on age, and suggested that the obligatory criteria of exercise EGG evaluation for men could not be extended to women.

Epidemiological suspicion of coronary disease was more frequent, due primarily to the higher incidence of angina of effort and probable ischemia in the exercise EGG. In view of the specific occupational exposure of these persons to zinc, cadmium, and lead, we attempted to determine whether the appearance of signs of coronary disease is dependent on these factors. In those persons working with cadmium, we found a significantly higher incidence of signs of pain after exercise and more frequent (although not statistically significant) signs of ischemia in the exercise EGG. The relation between environmental contamination with cadmium and the occurrence of coronary disease has been recognized in the literature for years [19]. Studies of 28 American men showed a significantly higher mortality due to arteriosclerotic disease in cities with elevated levels of cadmium pollution in the air [2].

The effect of lead on the cardiovascular system has been described by numerous authors [15, 19]. There is no convincing proof, however, that this element has a definite effect on the onset or course of coronary disease. Among our workers, signs of ischemia in the exercise EGG were even rarer in persons exposed to high levels of lead. It is also possible that lead itself is responsible for the high incidence of less specific irregularities in the ST-T segment and other electrocardiographic signs not discussed in this report, via its effect on the sympathetic nervous system and the heart muscle [7].

A beneficial effect of zinc on the course of arteriosclerosis and its complications was suggested by other authors [19]. This was confirmed in the population which we studied. In workers exposed to zinc, in addition to more frequent elevated blood pressure levels [17], there was a lower incidence of subjective and electrocardiographic signs of coronary disease.

Conclusions

  1. The use of the exercise test to detect coronary risk made it possible to better identify an additional group of persons requiring preventive or therapeutic measures.
  2. An evaluation of the population exposed to cadmium, zinc, and lead indicates that cadmium may increase the incidence of signs of coronary disease, while zinc may decrease it.
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