European Journal of Cardiovascular Medicine

Serum thyroid-stimulating hormone (TSH) levels over the upper limit of normal in the presence of normal serum free thyroxine levels are referred to as subclinical hypothyroidism (SCH). [1] 3% to 8% of people without a documented thyroid condition have subclinical hypothyroidism, or mild thyroid insufficiency, which is a prevalent issue.[2,3] The frequency of SCH rises with age and is more common in women. Men begin to approach women in terms of prevalence after the sixth decade of life, with a combined prevalence of 10%. Eighty percent of SCH patients have antithyroid antibodies, and eighty percent of them have serum TSH levels below 10 mIU/L.

There is mounting proof that SCH raises cardiovascular risk due to lipid imbalances, especially in older women.[4,5] Elevated incidence of coronary heart disease and early atherosclerosis are linked to clinical hypothyroidism. This is caused, at least in part, by the lipid abnormalities that are frequently observed in hypothyroidism. [6,7] Other than dyslipidemia, hypothyroidism and atherosclerosis may be linked by thyroid hormone effects on coagulation, vasodilation, parasympathetic function, and homocysteine metabolism.[4,8] In a study examining the relationship between euthyroid patients’ TSH levels and cardiovascular disease, it was discovered that patients who had coronary events had considerably greater TSH than controls who were matched for body mass index, age, and gender.[9] The cross-sectional Rotterdam study revealed a link between SCH and aortic calcification & myocardial infarction.[10] It has long been questioned whether SCH is independently related with ischemic heart disease (IHD), as multiple observational studies comparing the outcomes of SCH individuals with euthyroid participants have yielded different results.[11,12] If there is really an association, this presents a significant public health concern for the elderly population, where SCH is most common.[2] As results of multiple studies show its impact on ischemic heart disease, we attempted to look at the prevalence of SCH in individuals who had suffered an acute myocardial infarction.

This cross-sectional prospective study was conducted on acute myocardial infarction patients attending Medicine OPD or intensive cardiac care unit (ICCU) or admitted in MLN Medical College and its associated S R N Hospital, Uttar Pradesh, India from the period of August 2015 to August 2017. The study was carried out in accordance with the ethical standards on human experimentation. Data collection was started after obtaining ethical clearance from institutional ethics committee. A written informed consent in English and Hindi was taken from all the participants in the study. The subjects were properly told about the purpose of the study and this was done for good clinical practice.

200 adult patients (age > 18 years) with acute myocardial infarction and including both males and females were selected from the patients attending Medicine OPD or intensive cardiac care unit (ICCU) or admitted in S.R.N. Hospital as a case of AMI. All Acute Myocardial Infarction Patients whether euthyroid or SCH based on TSH level between 6-10μIU/ml and normal T4 value 4.9-12.5 μg/dl were included in the study. Patients with TSH values > 20mU/L or < 4.5mU/L, known cases of hyperthyroid diseases (graves disease, toxic multinodular goiter) or hypothyroid diseases (pituitary adenoma), drug induced hypothyroidism (lithium, phenytoin, rifampin) and chronic autoimmune thyroiditis were excluded from the study. Clinical examination of patients was done consisting of medical history, physical examination and anthropometric measurements. Laboratory data included electrocardiogram, chest x-ray, lipid profile, blood sugar, renal function tests and thyroid function tests. All laboratory investigations were collected at the time of admission to the hospital. Patients were classified into 2 groups based on their thyroid function tests.

– Group-I TSH Level >4.5 to 9.9mU/L .

– Group-II TSH Level >10 to 20mU/L .

For measuring biochemical parameters, blood samples were collected from all participants after 12 hours overnight fasting. The samples were immediately centrifuged at 3000 rpm for 5 min and serum was separated. The sera were stored at -20° C until assayed. Serum T3, T4 and TSH levels were measured by the enzyme-linked immunosorbent assay (ELISA) method using commercial kits. The normal range for TSH is 0.39-5.95 μIU/ml and for T3 and T4 are 55-200 ng/ dl and 4.9-12.5 μg/ dl, respectively.

Statistical analysis was done by SPSS software using descriptive analysis and chi-square test. A p-value<0.05 was considered to be statistically significant.

The study included 200 acute MI patients from August 2015 to August 2017. Out of 200

patients, 146(73%) were males and 54(27%) were females with male:female ratio of 2.703:1.

Figure 1: Gender distribution of MI patients

Table 1 shows Age distribution of MI patients. As can be seen, 83 patients were in 51-60 years age group, 56 patients were between 61-70 years, 47 were in 40-50 years age group and remaining 14 patients were above 70 years of age.

Table1: Age distribution of MI patients

Table 2 shows the association of age and gender in myocardial infarction patients. In 40-50 years age category 36 patients were males and 11 were females. The proportion of males and females in 51-60 years age category was 26.0% and 15.5% respectively. In patents of 61-70 years, number of male patients was 48 and that of female patients was 8. Least number of patients was there above 70 years of age with males and females being 10 and 4 respectively. Myocardial infarction was found significantly associated (p< 0.05) with the gender of the patients.

Table2: Association of age and gender in myocardial infarction patients

Figure 2 depicts the prevalence of SCH in MI patients. Out of total 200 MI patients 32(16%) were having SCH and 168(84%) were euthyroid Patients. It is clear from the table that the prevalence of SCH in MI patients is 16%.

Figure 2: Prevalence of SCH in MI patients

Out of 200 Patients, number of SCH Patients presenting with STEMI was 21(10.5%) and number of SCH Patients presenting with NSTEMI was 11(5.5%). Euthyroid patients presenting with STEMI Myocardial infarction were 134(67%) and euthyroid patients presenting with NSTEMI were 34(17%). No significant association (p=.079) was found between SCH and Myocardial infarction.

Table 3: Association of SCH with STEMI and NSTEMI

Among patients with SCH, 21(65.6%) were males and 11(34.4%) were females. Out of 21 male patients, 14 were having STEMI and 7 were having NSTEMI. Out of 11 female SCH patients, 7 were having STEMI and 4 were having NSTEMI. The association of gender of SCH with type of MI was found to be non-significant.

Table 4: Association of gender of SCH with STEMI and NSTEMI

Present study was a descriptive study aiming to evaluate SCH prevalence among patients with acute MI conducted on 200 MI patients admitted in MLN Medical College and its associated S R N Hospital, Uttar Pradesh, India from the period of August 2015 to August 2017. Subclinical hypothyroidism is a common clinical problem, recognized by abnormally high serum TSH value with normal FT4 and FT3 concentrations. It was recently reported that SCH is associated with elevated risks of cardiovascular events, cardiac dysfunction, lipid metabolism abnormalities and neuropsychiatric disorders, it is still debated whether long-term subclinical hypothyroidism is associated with systemic complications. In our study, MI was found to affect more males than females. This is in accordance with a study done by Okuyan Ertugrul et al. [13] Our study is also in concordant with a study done by Vijay Kumar Sah et al. who showed male (58%) were predominant for MI than female (42%).[14] Similar findings were found in a survey done by national health and nutrition examination survey. [15] These findings may be attributed to increase stress and cigarette smoking and/or use of other tobacco products. Our study is contradictory to a study done by Lerner DJ and Kannel WB who showed that women had higher rates of atypical presentations such paroxysmal dyspnea, or congestive heart failure (CHF).[16]

Our study revealed that patients belonging to age group 51-60 (41.5%) were more prone to MI which is almost supported by a study done by Ng M et al who reported men aged 40–49 years and women aged 50–59 years experience an increase in incidence of MI. One explanation of these remarkable findings could be the imbalance in changing risk factors for MI; obesity and diabetes, for example, are increasing in society.[17] This is contradictory to the study by Vijay Kumar Sah et al. as they reported patients belonging to >60 age group were more prone to cardiovascular problems.[14]

Regarding prevalence of SCH, this study showed that the prevalence of SCH was 16% among the MI patients (including both STEMI, and NSTEMI). These results are supported by Cooper and Biondi study which showed that the prevalence of SCH in adults has been reported to range from 4% to 20%. This wide range can be explained by differences in age, gender, race, body mass index, and dietary iodine intake in the studied populations as well as differences in serum TSH evaluation methods.[18] Our results are also concordant with the results of the Colorado study in which the prevalence of SCH ranged from 4 to 21% in women and 3 to 16% in men.[19] However, our results are disconcordant with the results of Whickham Survey [20]  and NHANES III [21] which showed higher prevalence of SCH in older population.

Our study showed that the prevalence of Euthyroid patients was 84% among the whole MI patients (STEMI, and NSTEMI). Mohammed Mansour Helmy et al. also showed higher prevalence of Euthyroid Patients (81%) in comparison with SCH Patients where he conducted a study on 300 Patients.[22]

In our study we observed that out of 200 patients with MI, SCH patients presenting with STEMI was 21(65.6%) while patient presenting with NSTEMI was 11(34.4%). This is in support of the findings done by Vijay umar Sah et al who found 18 out of 25(72%) in STEMI group and 7 out of 25(28%) in NSTEMI group.[14] Similar finding were observed by Tuzun D et al.[23] In our study we also observed that out of 200 Patients with MI, Euthyroid Patients presenting with STEMI was 134 (79.7%) while Patient Presenting with NSTEMI was 34 (20.3%). In a study of 400 patients almost similar findings were observed by Vijay kumar Sah et al who reported 10 (66.67%) patients belonged to STEMI group while 5(33.33%) belonged to NSTEMI group.[14] Tuzun D et al. in their study of 94 patients did not find any significant difference in prevalence of Euthyroid between STEMI and NSTEMI groups.[23] However our study was contradictory to a study done by Mathur P et al. who reported higher prevalence 12 out of 18(66.66%) in NSTEMI group and it was 6 out of 18 (33.34%) in STEMI group.[24]

In our study we found that out of 32 SCH Patients, Male patient with STEMI were 14(43.8%) and female Patient with STEMI were 7(21.9%) while Male patient with NSTEMI were 7(21.9%) and female Patient with NSTEMI were 4(12.5%). No Significant association was observed between gender with SCH and the MI with STEMI and NSTEMI. Not many figures are available about study on association between gender of SCH Patients with STEMI and NSTEMI so further studies are required to substantiate these findings.

Our study showed that SCH Patients presenting with STEMI Myocardial infarction were 21(10.5%) and SCH Patients presenting with NSTEMI Myocardial infarction were 11(5.5%) while Euthyroid Patients presenting with STEMI Myocardial infarction were 134(67%) and Euthyroid Patients presenting with NSTEMI Myocardial infarction were 34(17%). So out of 200 patients, overall patients presenting with STEMI was 155(77.5%) in SCH and euthyroid patients while patients presenting with NSTEMI was 45(22.5% ) in SCH and euthyroid patients. As discussed above these findings were in concordancy with a study done by Vijay kumar Sah et al, Tuzun D et al.[14,23]

In conclusion, there is male predominance in MI. A higher prevalence of MI was seen in age group 51-60 yearsThis study depicts subclinical hypothyroidism were observed in 16% of MI patients and Euthyroid was observed in 84% Patients. No gender difference was noted in abnormal thyroid hormone profile in male and female group. A statistically higher prevalence of STEMI was seen in SCH and Euthyroid Patients (77.5%) as compared to NSTEMI in SCH and Euthyroid Patients (22.5%). These findings suggest that there is greater risk of thrombosis, and hence of myocardial infarction, in moderate hypothyroidism, and greater risk of hemorrhage in severe hypothyroidism. The features of this study concluded that hypothyroidism may be associated with MI. So, thyroid hormone levels should be observed in all middle aged population for early diagnosis of cardiac involvement. This may be helpful for better management of the MI patients. Physicians should also be encouraged to educate the people about the risks of diabetes, hypertension and smoking.

Conflict o interest: None

Source of funding: Nil

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