Link between Thyroid Dysfunction and Heart Disease

The thyroid gland is a butterfly-shaped small gland in the front of the neck, just below the Adam’s apple and is less than 20 grams in weight. It is a very important organ that produces hormones that regulates many of the body’s functions: These include regulation of the body’s metabolic rate, which controls how the body uses energy and affects weight and digestion.

It also regulates the body temperature, heart rate and blood pressure. Besides this it is responsible for bone health by producing calcitonin, a regulator of calcium metabolism. In addition, it also has important role in regulating the menstrual cycle and regulation of other hormones of the body.

The thyroid gland produces two main hormones: triiodothyronine (T3) and thyroxine (T4). The pituitary gland, located at the bottom of the brain, produces thyroid-stimulating hormone (TSH), which tells the thyroid how much hormone to produce. Iodine is an important component of T3 and T4. As the thyroid gland is a very thin and soft organ, it is usually not noticeable. However, even the slightest swelling in the thyroid gland becomes palpable.

A larger amount of swelling becomes visible to the naked eye. Many people, therefore, suspect a thyroid disorder because of “swelling in the neck.” This is also called a “goitre”. Thyroid hormones play an important role in the development of foetuses and also induce growth in children. Thyroid deficient children have peculiar physical characteristics are sluggish sleepy with very slow growth and are often mentally deficient. They are also called “Cretins”.

Thyroid Disorders and its Effects on Heart and blood circulation:

The Derangements of thyroid function can be either reduced or hypo functioning or Increased activity or hyper functioning. The Disorders are therefore designated as: Hypothyroidism (Reduced functioning) and Hyperthyroidism (Increased functioning)

Hypothyroidism:

It is a common medical problem with a reported prevalence of around 11% in India, which is much higher than the figure of 2 to 4.6% in Europe and USA. Here are some other facts about hypothyroidism in India. The highest prevalence of hypothyroidism is in people aged 46-54 years. Nearly one-third of patients with hypothyroidism in India remain undiagnosed and untreated. Iodine deficiency was previously blamed for the occurrence of hypothyroidism in India, but the disease is still prevalent despite the promotion of iodized salt since 1983.

The figures are higher in Kashmir valley. According to a study of 2016, reported by Dr Nazir Ahmad Malla and Dr Peerzada Mohammad Shafi, its prevalence was 16.18%, with higher figures in the rural population (18.45%) than the urban (11.63%). Prevalence of hypothyroidism was more as age of patients increased. It was more among females than males.

The hypo function of thyroid gland often leads to slow heart rate and low blood pressure. Neither of these signs usually produces symptoms in patients. Prolonged hypothyroidism causes metabolic changes in the body and may produce elevated levels of cholesterol. Frequent accompanying symptoms are fatigue, obesity and cold intolerance.

We are aware that some types of elevated cholesterol levels may produce or aggravate narrowing of the coronary arteries. However, as heart rate and blood pressure are also lowered, the complications of angina or heart attack are relatively uncommon. Hypothyroidism being so common in general population often patients with high BP also have this problem.

 Complications:

In severe prolonged hypothyroidism the heart muscle cells and fibres may become diseased with the development of a weak heart producing heart failure. There is often a collection of fluid around the heart, called a pericardial effusion which rarely produces any symptoms. This is diagnosed by echocardiography. The high cholesterol and triglyceride levels associated can increase the risk for coronary artery disease, but the importance of this is not fully understood. The occurrence of heart complications is more likely to occur in patients who have underlying heart disease caused by factors other than their thyroid problem.

In a recent study we have demonstrated that undiagnosed hypothyroidism was frequently seen in patients admitted with heart attacks and had an important prognostic bearing.

 Treatment: Once the diagnosis is confirmed by blood tests the treatment is simple. It consists of replacement of the deficiency with thyroid hormone preparations.

These are thyroxin or its synthetic counterparts. The treatment has to be regulated by periodic estimation of the TSH by doing a blood test. Once the hormone levels are corrected the problem is overcome. However, the replacement has to continue long term regulated by periodic estimation of TSH and a regular follow up is needed.

Hyperthyroidism

Increased levels of thyroxine released from the thyroid gland stimulate the heart to beat rapidly and more strongly. This usually produce a fast heart rate which is called tachycardia. This is observed by a physician and may usually not be noticed by the patient. However, if the fast heart rate becomes severe then palpitations may be observed by the patient as if he or she is exercising or anxious. Palpitations may occur in other types of heart disease, but, if caused by an overactive thyroid gland it does not necessarily mean that a more serious underlying heart disease is present.

In some patients, prolonged stimulation of the heart with thyroxine may cause an incoordination of the conduction of electrical impulses within the heart and atrial fibrillation may ensue. It leads to a rapid and chaotic heart beat and pulse and needs an early recognition.

Hyperthyroidism is also often associated with losing weight despite a good appetite, intolerance to heat, excessive sweating and tremulousness of hands and fingers. There are often bulging eyes associated with this problem called exophthalmos. It is also called “Grave’s disease”.

Prolonged stimulation of heart contraction can cause some increase in blood pressure which is called systolic hypertension. The diastolic blood pressure, that is the lower of the two blood pressure readings, is not normally increased. The increased contraction of the heart with increased cardiac output causes a pulse that is easily felt at the wrist and contributes to warm sweaty hands. Permanent changes in the heart are unusual in patients with normal healthy hearts, unless the thyroid disease is particularly severe and left untreated for very long periods of time.

The diagnosis is again confirmed by assessing the thyroid hormone levels in blood which get increased (T3 and T4) and the TSH levels get low. A thyroid scan is also often done and corroborates the diagnosis and can establish inflammation as a cause.

Treatment

The principle is to correct the hyperthyroidism. Specific treatment to reduce the effects of high level of the hormone is needed.

Before starting specific drugs like neo-mercazole, measures to reduce heart rate by using beta blocking drugs (propranolol, metoprolol etc) are often used.

These drugs are also useful to decrease other symptoms of hyperthyroidism such as finger tremor and anxiety.

Patients with heart failure need the guideline directed treatment for the underlying heart condition. Hyperthyroidism if associated worsens it and needs treatment separately.

The decision whether to use drugs, radioactive iodine therapy, or thyroid surgery, depends on the nature of the thyroid problem and is best decided by the treating physician, who takes into account various factors like the age, the underlying cause and patient’s desire.

Author is Founder Director Gauri Kaul Foundation