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ORIGINAL ARTICLE
Year : 2013  |  Volume : 6  |  Issue : 3  |  Page : 250-253  

Lipid profile and electrocardiographic changes in thyroid dysfunction


Department of Medicine, Padmashree Dr. D. Y. Patil Medical College, Hospital and Research Centre, (Dr. D.Y. Patil Vidyapeeth), Pune, Maharashtra, India

Date of Web Publication5-Jul-2013

Correspondence Address:
Prasanna K Satpathy
Department of Medicine, Padmashree, Dr. D.Y. Patil Hospital, (Dr. D.Y. Patil Vidyapeeth) Pimpri, Pune - 411 018, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0975-2870.114647

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  Abstract 

Background: The study was designed to explore lipid profile and electrocardiographic changes associated with thyroid dysfunctions. Materials and Methods: A total of 72 patients of thyroid dysfunction having either hypothyroidism or hyperthyroidism were investigated with lipid profiles and electrocardiogram (ECG). Hypothyroids with ST-T ECG changes who were symptomatic for coronary artery disease were subjected to further investigations and were benefitted by either medical therapy or revascularization procedures following coronary angiography. Results: Out of the 72 patients, 44 (61.11%) were suffering from hypothyroidism, while hyperthyroidism was present in 28 (38.89%). Female:male ratio was 4.5:1. Maximum number of hypothyroid patients (73%) had either borderline high (36.6%) or high (36.36%) serum cholesterol; 67.86% of the 28 hyperthyroid patients had serum cholesterol levels <200 mg%. In hypothyroidism, ST segment and T wave ECG changes (ST-T changes) were the commonest electrocardiographic findings. Conclusion: Hypothyroidism was associated with high serum cholesterol levels whereas maximum patients with hyperthyroidism had normal serum cholesterol levels. Correlation was found between ST-T changes on ECG and high serum cholesterol levels in hypothyroidism.

Keywords: Coronary artery disease, electrocardiographic changes, hyperthyroidism, hypothyroidism, lipid profile, ST segment and T wave changes


How to cite this article:
Satpathy PK, Diggikar PM, Sachdeva V, Laddha M, Agarwal A, Singh H. Lipid profile and electrocardiographic changes in thyroid dysfunction. Med J DY Patil Univ 2013;6:250-3

How to cite this URL:
Satpathy PK, Diggikar PM, Sachdeva V, Laddha M, Agarwal A, Singh H. Lipid profile and electrocardiographic changes in thyroid dysfunction. Med J DY Patil Univ [serial online] 2013 [cited 2019 Jul 23];6:250-3. Available from: http://www.mjdrdypu.org/text.asp?2013/6/3/250/114647


  Introduction Top


There are multiple systems on which thyroid hormone acts or contributes to their function but heart and the vessels are the major target organs. Marked changes in these organs occur in patients with thyroid dysfunction. [1] Many symptoms and signs recognized in patients with overt hyperthyroidism and hypothyroidism are due to increased or reduced action of thyroid hormones on heart and vascular system. [2] It is also seen that overt hypothyroidism is characterized by hypercholesterolemia and a marked increase in low-density lipoproteins (LDLs) and apolipoprotein B. The reported mechanisms for the development of hypercholesterolemia in hypothyroidism include decreased fractional clearance of LDL by a reduced number of LDL receptors in the liver in addition to decreased receptor activity. [3],[4],[5] In thyroid disease, dyslipidemia coexists with various metabolic abnormalities and induce insulin resistance and oxidative stress via a vicious cycle. The above associations in combination with the thyroid hormones-induced hemodynamic alterations might explain the increased risk of coronary artery disease (CAD), cerebral ischemia risk, in patients with overt or subclinical hypothyroidism. [6] Most of the existing studies support lower total and LDL cholesterol levels in patients with hyperthyroidism. [7],[8],[9] Recognized electrocardiogram (ECG) changes in hyperthyroidism include tachycardia, arrhythmias and non-specific T-wave changes. ST segment changes are not well documented. [2],[3] Common ECG changes in hypothyroidism are bradycardia, low voltage complex, ST segment depression, QT interval lengthening and increased QT dispersion, flattening or inversion of T wave, which reflects the prolonged cardiac action potential. In addition, these patients are more prone to ventricular arrhythmias particularly in presence of ischemic heart disease, due to increased electrical depression in myocardium. [10],[11],[12] Also in hypothyroidism there is QRS prolongation, right bundle branch block and infrequently Torsades de pointes. [13]


  Materials and Methods Top


A total of 72 consecutive fresh cases of thyroid disorders diagnosed as hypothyroidism and hyperthyroidism by their clinical presentation and thyroid function tests were studied for the cardiovascular manifestations. Out of these, 44 cases were of hypothyroidism and 28 cases were of hyperthyroidism. Patients of both sexes and above 13 years of age were included. Pre-existing heart diseases like rheumatic heart disease, congenital heart disease, ischemic heart disease, hypertensive heart disease, cardiomyopathy, with co-morbid thyroid diseases, diabetes mellitus, chronic smokers, metabolic syndrome, and morbid obesity were excluded. Cardinal symptoms of ischemic heart disease were recorded. Investigations included T3, T4, free T3, free T4, thyroid stimulating hormone, fasting lipid profile, ECG, and Echocardiography in few cases.

Fractional shortening (FS) of the left ventricular (LV) muscular fibres was calculated by:

FS = (LVEDD-LVESD)/LVEDD *100

LVEDD - Left ventricular end diastolic diameter.

LVESD - Left ventricular end systolic diameter.

Statistical Analysis

Data were compiled and analysed. Differences in lipid profile and echo findings between hypothyroid and hyperthyroid patients were tested for statistical significance by two sample t-test along with 95% confidence intervals of the mean difference.


  Results Top


Age and Gender Distribution

Amongst 72 thyroid dysfunction patients, youngest patient was a 15-year-old female and oldest was a 65-year-old female, with peak incidence of thyroid dysfunction in 3 rd and 4 th decade [Table 1].
Table 1: Age and sex distribution of patients of hypothyroidism and hyperthyroidism

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Lipid Profile

The differences in lipid profile are shown in [Table 2]. Total cholesterol (TC), triglycerides (TG) and LDL were significantly higher in hypothyroids, while high density lipoprotein (HDL) was significantly lower.
Table 2: Total cholesterol, triglycerides, highdensity lipoprotein and low density lipoprotein (mg%)

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ECG Findings in Hypothyroids

Horizontal ST segment depression of 1 mm or more 0.08 s from the J-point with T wave inversion was the commonest ECG finding in 15 hypothyroids (34%); 3 (7%) in anterior LV wall leads, 4 (9%) in inferior LV wall leads and 8 (18%) in inferolateral LV wall leads. 10 (23%) Hypothyroids had sinus bradycardia in ECG, being the second commonest ECG abnormality [Table 3]. All hypothyroids with ST-T changes had stable angina.
Table 3: Electrocardiographic findings in hypothyroidism (n=44)

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ECG Findings in Hyperthyroids

Sinus tachycardia was the commonest ECG finding in the hyperthyroids (60.71%); atrial fibrillation (AF) in 21.43% of these patients; LV hypertrophy in 42.86%; LV strain in 21.43% [Table 4].
Table 4: Electrocardiographic findings in hyperthyroidism

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Echocardiography Findings

The major differences in echocardiography are shown in [Table 5]. FS, and ejection fraction (EF) were significantly lower in hypothyroid patients compared with hyperthyroid subjects, while there was no significant difference in LV internal dimensions (both systole and diastole).
Table 5: Fractional shortening, ejection fraction, left ventricular internal dimension (diastole) and left ventricular internal dimension (systole)

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  Discussion Top


In 1900, Von Noorden from Vienna, stated that thyroid played a key role in causation of 'fatty disease'. [14] In 1918, scientists ascertained correlation of blood cholesterol to the secretion of adrenals and thyroid. In 1930s the connection of cholesterol with thyroid function and disease was observed. [15] On Christmas day of 1930, a landmark article was published by Mason and colleagues in the New England Journal of Medicine which showed the significance of cholesterol values in hypothyroidism and hyperthyroidism. [16] In a multicentre study of prevalence of hypothyroidism in 752 hyperchloremic patients, primary hypothyroidism occurred in 3.7%. [17] In contrast, in thyrotoxicosis, cholesterol synthesis in increased, but this is simultaneously counter-balanced by an increased rate of degradation and excretion. [18]

The lipid profile in hypothyroidism in characterized by increased total and LDL cholesterol with increased or normal HDL levels involving HDL2 sub fraction. [19],[20] TG levels are not affected or are slightly elevated. [21] The most frequent form of dyslipidemia, as shown in a study of 295 hypothyroid patients is pure hypercholesterolemia (56%), followed by combined hypercholesterolemiaand hypertriglyceridemia (34%) and isolated hypertriglyceridemia (1.5%), only 8.5% had no lipid abnormalities. [21] In our study 70% had hypercholesterolemia and hypertriglyceridemia, 23% no lipid abnormality, 7% pure hypercholesterolemia. This disparity may be due to small sample size. Most hypothyroidsin our study had reduced HDL levels; only 14% had marginally elevated values.

In hyperthyroidism, an increase in synthesis and degradation of lipids occurs, with a pre-dominance of degradation. Therefore, plasma levels of lipids are reduced in hyperthyroids. [22] Although this finding can be partly attributed to malnutrition and weight loss, the high uptake of cholesterol into cells and its larger excretion in bile salts through the gut can all contribute to the hypolipemic effect. [23] HDL, specially HDL2 sub fraction is reduced in hyperthyroidism. [20] Mild hypertriglyceridemia has been paradoxically observed in hyperthyroidism due to direct stimulation of hepatic lipogenesis by thyroid hormones. [24] In this study 32%hyperthyroids had both hypercholesterolemia and hypertriglyceridemia, 68% had elevated HDL levels. This is possibly due to a small sample size.

Thyroid hormones have significant effect on the heart and cardiovascular system. [3] The most common clinical signs are a narrowed pulse pressure, diastolic hypertension, low cardiac output, reduced EF impaired diastolic function and bradycardia. [25] Overt hypothyroidism is associated with accelerated atherosclerosis and CAD due to hypercholesterolemia and diastolic hypertension. [26],[27],[28],[29] A prospective study from Japan showed an increase risk of ischemic heart disease in men but not women with subclinical hypothyroidism. [30] A prospective study in the United States, followed up men and women age 65 or older for more than 10 years showed no influence of hypothyroidism (overt or subclinical) on cardiovascular outcome and mortality. [31] In this study, 34% of hypothyroids showed significant ST-T ECG changes with angina and CAD on subsequent investigation. Reduced EF and diastolic dysfunction were also significant in this study.

In hyperthyroids, sinus tachycardia, AF, wide pulse pressure, dyspnoea on exertion, exercise intolerance are common. [3] Increased LV mass due to sustained volume overload with resultant cardiac work occurs in hyperthyroids. [32] This may cause ST-T ECG changes due to LV strain. Plasma lipids (TC and LDL cholesterol) are reduced in hyperthyroidism and this is responsible for anti-atherogenic effect and there is less chance of accelerated atherosclerosis and CAD. In this study, sinus tachycardia was the commonest ECG finding (61%), LV chamber hypertrophy was the second common abnormality (43%). ST-T ECG changes are due to LV strain occurs in 21% of cases of hyperthyroidism.


  Conclusion Top


'There was oedema of the skin...much serous effusion in the pericardium...the heart was large...the arteries were everywhere thickened, the larger ones atheromatous.'. [33] This was the autopsy finding of diffuse atherosclerosis in a 58-year-old woman of hypothyroidism. Hypothyroidism is associated with significant increased level of atherogenic lipids. Serum lipids with good correlation with ischemic ST-T segment ECG changes are suggestive of CAD. Hyperthyroidism is associated with significantly low serum cholesterol and LDL cholesterol. The present study findings are in conformity with earlier studies.

 
  References Top

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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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