The Impact of Subclinical Hypothyroidism on Cardiovascular System
The Impact of Subclinical Hypothyroidism on Cardiovascular System
This research aims to evaluate the relation between SCH and cardiovascular System by
 assessment of lipid profile and carotid intima-media thickness (CIMT), as a marker of
 atherosclerosis, and endothelial function.
Subclinical hypothyroidism (SCH) is defined as a condition that characterized by elevated
 serum thyroid-stimulating hormone (TSH) concentrations (TSH: >4.5 mu/l), while circulating
 thyroxine (T4) and tri- iodothyronine (T3) levels remain within the normal range.

 Depending on the extent of serum TSH elevation, SCH can be divided into Mild (where the
 concentration of serum TSH is in the range of 4.5-9 mU/l) Severe (TSH≥10 mU/l) SCH. Mild SCH
 constitutes ~75% of the total number of patients with SCH. The incidence of SCH varies
 between 5 and 10 % depending upon the gender, age, more frequent in women than in men, with
 increasing prevalence with advanced age in both sexes The consequences of SCH are variable at
 several levels and may depend on the duration and the degree of increasing level of the serum
 TSH. However, a number of important questions about SCH remain, including whether it
 increases cardiovascular (CVS) risk or not.

 SCH has many causes the most common (60% to 80%) is chronic autoimmune thyroiditis associated
 with the presence of circulating anti-thyroid peroxidase antibodies(TPOAb) that are the most
 sensitive serological test for thyroid autoimmunity and/or antithyroglobulin
 Antibodies(TgAb).

 The association between subclinical hypothyroidism (SCH) and cardiovascular disease has
 received increasing attention in recent years.

 Thyroid hormones exert a direct effect on the heart and blood vessels. The deficit of these
 hormones leads to functional disorders of the Cardiovascular System (CVS) such as changes in
 cardiac frequency, cardiac output, left ventricular diastolic dysfunction, and reduced
 resting and exceptional systolic function.

 Vascular abnormalities, such as increased vascular resistance, arterial stiffness,
 endothelial dysfunction, that is considered to be an early step in the development and
 progression of atherosclerosis.

 The early changes in patients with SCH is alteration in lipid profile that could be a
 contributing factor for the risk of atherosclerosis, hyperlipidemia is one of the common
 causal factors of endothelial dysfunction.

 Elevation of TSH has a positive correlation with serum total cholesterol (TC), triglycerides,
 LDL cholesterol (LDL-C), and a negative correlation to HDL cholesterol.

 Some studies found significant lipid profile changes in patients with SCH, some others did
 not.

 Atherosclerosis is a diffuse, degenerative disease of the arteries that results in the
 formation of porridge-like lipid deposit plaques in the great arterial wall, and accounts for
 the majority of cardiovascular disease incidence. Therefore, this association is the first to
 be assessed for the link between SCH and cardiovascular disease.

 Progression of atherosclerosis features a chronic unresolved inflammatory response, leading
 to stenosis, embolization and thrombosis, since atherosclerosis is a chronic disease, to
 observe the whole pathogenesis in one single investigation would require a long time of study
 .Thus, endothelial dysfunction, as one of the earliest signs for atherosclerosis, could be
 most frequently observed in clinical investigation Assessment of endothelial dysfunction,
 being an early biomarker, is helpful in predicting cardiovascular risk by Carotid artery
 intima-media thickness (CIMT) measurement that has increasingly been used as a marker of
 atherosclerosis in many studies.

 Evidence supporting the correlation between SCH and atherosclerosis has been accumulating:

 The first study regarding the associated cardiovascular risk in patients with SCH was the
 long-time large cross-sectional Rotterdam study in the Netherlands, which showed an increased
 risk for atherosclerosis and prevalence of myocardial infarction among female patients with
 SCH aged >55 years. Velkoska and his colleagues who reported that SCH is associated with
 increase in CIMT and presence of carotid plaques independent of traditional atherosclerosis
 risk factors, Onder et al. who showed lack of a significant difference in CIMT between over
 and subclinical hypothyroid, indicating that the inflammation leading to increased CIMT
 starts in the subclinical phase .
Inclusion Criteria:

 -  All healthy adult who will be diagnosed as SCH along with age ≥18 & gender-matched
 healthy relatives with normal thyroid function will be screened for evidence of high
 cardiovascular risk.

 Exclusion Criteria:

 -  Hypo or hyper-thyroidism, Diabetes, Hypertension, cardiovascular disease, smokers,
 pregnant and lactating women.

 Patients who had been treated with anti-thyroid drugs, radio iodine therapy or thyroxin
 hormone supplement or who had under gone thyroid surgery, those with a history of thyroid
 cancer or head and neck malignancies.

 Those with history of drug use such as Contraceptive pill, Anti-depressant drugs,
 Corticosteroids, Anti arrhythmic drugs.