Heart Rate Variability in Hyperthyroid Patients correlated with Thyroid Function Tests

Rashmi, R (2013) Heart Rate Variability in Hyperthyroid Patients correlated with Thyroid Function Tests. Masters thesis, PSG Institute of Medical Sciences and Research, Coimbatore.

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Abstract

INTRODUCTION: The thyroid is a highly vascular, brownish-red structure located in the neck anteriorly extending from fifth cervical vertebra to the first thoracic vertebra. Thyroid gland is the largest gland which is essential to sustain normal life. Thyroid is a greek word meaning "shield", introduced by Thomas Wharton. Thyroid gland consists of follicles lined by cuboidal epithelium. Each follicle contains clear proteinaceous colloid material. The colloid consists of mainly thyroglobulin. Iodide plays a important role in thyroid synthesis. About 120 μg of iodide enter thyroid gland per day. The iodide pump or Na +/I- (sodium iodide symporter) reabsorbs iodide into thyrocytes against electrical gradient. Iodine is immediately bound to the tyrosine in the thyroglobulin3. Thyroglobulin is iodinated to form monoiodothyrosine (MIT) and diiodothyrosine (DIT). By coupling reactions, thyroxine (tetraiodothyronine) T4, triiodothyronine T3 and reverse T3 are formed. Thyroid peroxidase helps in both iodination and coupling reactions. At the peripheral tissues, triiodothyronine is produced from the deiodination of thyroxine . T3 has shorter half life but more active than T4. When the thyroid gland become overactive and synthesize excess of thyroid hormone ,it is called hyperthyroidism. The prevalence of hyperthyroidism has been estimated as 0.21 percent for men and 1.9 percent for women 4. The most common cause of hyperthyroidism in younger age group is Graves' disease. In graves the total daily disposal of T 3 is disproportionately increased relative to that of T 4 , indicating that the production rate of T 3 is increased. It could be due to increase in thyroid secretion of Triiodothyronine. Deiodinase -1 also causes increased peripheral conversion of T4 to T3 . Temporary viremia of thyroid gland, certain drugs, toxic nodules can also cause hyperthyroidism. Thyroid stimulating immunoglobulins are the antibodies that activate the TSH-receptor, thereby stimulating thyroid hormone synthesis and results in diffusely enlarged goiter. This is the etiology for graves disease. In most patients thyroid gland is massively enlarged or of normal size in a small fraction of patients. The consistency varies from soft to firm and rubbery. The surface may be lobular or smooth. Continous thrills and bruits at the upper or lower thyroid pole, due to increased blood flow ,which is suggestive of hyperthyroidism due to graves disease. AIM AND OBJECTIVES: Primary Aim: To investigate a possible relationship between hyperthyroidism and autonomic imbalance in hyperthyroid patients using spectral analysis of HRV. Secondary Aim: 1. To compare HRV of hyperthyroid and normal volunteers. 2. To assess the cardiovascular risk in hyperthyroid patients using HRV. Objective: 1. To compare HRV analysis between hyperthyroid and normal volunteers. 2. To study the type of autonomic imbalance in patients who are hyperthyroid. 3. To study the sympathetic influence in hyperthyroid and its role in the pathophysiology of cardiac complications. MATERIALS AND METHODOLOGY: This research study was carried out in our physiology laboratory, after getting ethical clearance from the institutional human ethics committee and informed consent from the subjects, in both hyperthyroid and control groups. The period of study was nine months. Inclusion Criteria: • Age between 30-50 yrs. • Body Mass Index- Between 18.5 to 25. • Both males & females who are Physically active. • Newly diagnosed 30 hyperthyroid patients with TSH less than 0.27 micro IU/ml. • 30 normal volunteers with TSH normal range. Exclusion Criteria: • Hypertensives. • Diabetics. • Patients on regular or irregular anti thyroid treatment. • The subjects who were on drugs affecting Autonomic Nervous System like anticholinergics, digoxin, minoxidil, theophylline, sympathomimetics, phenobarbitone. • Females who were psychiatric patients. • Those who were having BMI more than 25 and less than 18.5 Study Population: • Newly diagnosed hyperthyroid patients (before starting treatment) attending Medical Out Patient department and normal volunteers. • After getting clearance from Institutional Human Ethics Committee (IHEC) and Department of Clinical Research and Bioethics (DCRB) the subjects who fulfilled the criteria for study were taken for ECG recording and HRV analysis. • Thyroid Function Test reports, Age in years, Height in cms, Weight in kilograms of both Hyperthyroid and normal volunteers were collected. • A detailed history taking and a complete physical examination was done and a complete record was obtained for future verification. RESULTS: 60 patients were subjected t0 ECG recording. 30 patients were newly diagnosed hyperthyroid patients before starting treatment and 30 patients were euthyroid. 10 minute Elecro cardiogram was taken for all the 60 patients and HRV analysis was done. The HRV parameters (Time domain measures and the frequency domain measures) were compared between the cases and controls. Both HRV and thyroid hormone levels were compared, which gave the exact relationship between HRV and increased T3, T4 and decreased Thyroid Stimulating Harmone (TSH) levels. CONCLUSION: To our knowledge, this is the first study to investigate the autonomic innervations of the heart in thyrotoxicosis subjects using HRV analysis and comparison of BMR between the case and control groups. The results of our study show that there is reduced parasympathetic component and elevated sympathetic component in hyperthyroid patients. The cause is found to be the reduced levels of TSH levels as well as the increased thyroid hormones. In the view of present study results, disturbances of sympathetic branch of Autonomic Nervous System can be observed in patients with thyrotoxicosis. A predominance of sympathetic tone has cardio acceleratory effect and reduced beat-to-beat variations and therefore causes positive ionotrophic effects. Reduced Heart Rate variability is most commonly linked with a risk of arrhythmic death and it is the independent predictor of cardiac mortality and morbidity, but recent data suggests that any abnormal variability also predicts circulatory dysfunction, progression of coronary atherosclerosis and death due to arrythmias. The beta adrenergic blocking drugs reduce both cardiovascular and central nervous symptoms. It helps to reduce the anxiety while preparing patients for surgery. Beta-adrenergic blockers slow the resting heart rate from 97 to 80 beats/min and bring the rate of diastolic deceleration to normal. Beta blockers are usually prescribed to reduce the symptoms of thyrotoxicosis such as tachycardia, palpitations, tremors, anxiety. Anti-thyroid treatment given to decrease the synthesis of thyroid hormones , particularly, in the case of Graves' disease. We conclude that decreased vagal modulation on heart rate may occur in hyperthyroidism, which may be restored following adequate treatment of the disease by blocking beta receptors and there by inhibiting the adenylyl cyclasecyclic AMP pathway. This provides an attractive future option for management of arrhythmias and other cardiovascular complications due to thyrotoxicosis. From our study it is obvious that cardiovascular risk in thyrotoxicosis patients can be evaluated by our HRV analysis before any appreciable change occurred in heart rate itself. Prevention is better than cure. So even before the appearance of cardiac complications, they can be assessed and halted. Many randomised control trials can be done to bring out the unexplored effects of autonomic dysfunction on cardiovascular system. Thus cardiac morbidity can be assessed and treated earlier and mortality can be prevented using our HRV analysis.

Item Type: Thesis (Masters)
Uncontrolled Keywords: Heart Rate Variability ; Hyperthyroid Patients ; Thyroid Function Tests.
Subjects: MEDICAL > Physiology
Depositing User: Subramani R
Date Deposited: 28 Mar 2018 05:25
Last Modified: 31 Mar 2018 03:53
URI: http://repository-tnmgrmu.ac.in/id/eprint/6687

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