The endocrine system regulates most of the organs in our body. The influence of the thyroid gland on the heart is especially evident in various pathological conditions, the amount of thyroid hormones in the blood changes. But even in an absolutely healthy person, thyroxine plays a huge role for the full functioning of the myocardium. To better understand how the thyroid gland affects the heart, you need to explain a little about the physiology of this organ.

Physiology of the functioning of the thyroid gland

The thyroid gland is made up of thyrocytes. They have a huge number of enzymes, among which thyroid peroxidase stands out. This enzyme attaches iodine atoms to the protein tyrosine. The final stage of this reaction is the formation of thyroxine and triiodotyrosine. With the help of adenylate cyclase, the molecules of these substances leave the gland tissue into the systemic circulation, where, in conjunction with proteins, they are carried throughout the body.

Adequate intake of iodine is especially important for the normal functioning of the thyroid gland. Moreover, its amount should not exceed the norm, since this can lead to the development of neoplasms. On the other hand, the absence of disturbances in the feedback system of the thyroid gland with the pituitary gland is of great importance. An increase or decrease in the amount of thyrotropin not only regulates the activity of the synthesis of thyroid hormones, but is also the main biochemical marker of many diseases. The negative effect of the thyroid gland on the heart progresses over time and can lead to decompensation of its function.

Effects of thyroid hormones on the heart

Triiodothyronine is the most active form of thyroid hormone. When exposed to the heart, it produces the following biological effects:

• increases the uptake of glucose from the blood by the cells of the organ;
• stimulates glycolysis processes;
• enhances lipolysis, reduces the amount of fat in cells, inhibits its formation;
• increases the sensitivity of the myocardium to the effects of adrenal hormones – catecholamines (adrenaline, norepinephrine);
• in small quantities, it stimulates the synthesis of proteins (the presence of an anabolic effect);

• in high concentrations leads to protein breakdown and negative nitrogen balance;
• increases the efficiency of the myocardium during significant physical exertion;
• increases heart rate (HR) and blood pressure (BP);
• stimulates the growth and proliferation of myocardial tissues;
• increases the need for cells in oxygen;
• leads to an increase in the rate of metabolic processes.

Heart with thyrotoxicosis

It is important to consider that an increase in the level of thyroid hormones in various diseases leads to the development of thyrotoxic cardiomyopathy. It belongs to the group of metabolic pathologies of the heart. This disease can manifest itself only at a late stage of its development, which complicates its treatment. Modern research has shown that it most often occurs in the age group over 70 years old. There is a tendency for the development of cardiomyopathy to increase in adolescents. The following mechanisms lead to the progression of symptoms and a worsening of the general condition of the patient:

• excessive breakdown of proteins in myocardial cells;
• an increase in the number of receptors for catecholamines;
• stable increased load on the organ;
• development of dystrophic changes;
• replacement of normal myocardial tissue with connective fibers;
• progression of heart failure.

The first signs of the disease are nonspecific and it is difficult to distinguish them against the background of the general excitement of the patient, and neurological disorders. But gradually the following symptoms begin to bother the patient more and more:

• frequent dizziness;
• increased body temperature, sweating;
• the impossibility of long-term concentration at work;
• increased fatigue and general weakness;
• insomnia;
• headaches (most often in the temples);
• pain behind the sternum of a pressing or prickly character;
• shortness of breath on exertion;
• swelling of the limbs, which is worse in the evening;
• a feeling of palpitations and irregular heartbeats.

Clinical examination of such patients reveals:

• enlargement of the liver and spleen;
• persistent tachycardia (heart rate more than 100 in 1 minute);
• lability of the pulse during various physical activities;
• an increase in the size of the heart (especially to the left);
• the appearance of a systolic murmur over the base of the heart;
• accent 2 tones over the aorta;
• an increase in pulse pressure (the difference between systolic and diastolic blood pressure);
• atrial fibrillation;
• ventricular premature beats;
• dilatation and thinning of the walls of the heart chambers.

It is very important in hyperthyroidism to calm the rapid heartbeat and turn off the excessive exposure to catecholamines on the weakened myocardium. For this, beta blockers are used. Loop diuretics are also prescribed if heart failure develops.

The effect of hypothyroidism on the heart

It should be noted that a decrease in the level of thyroid hormones leads to the development of a hypothyroid heart. Among its causes, the most prominent are the inhibition of metabolic processes, the accumulation of mucoid in the tissues of the myocardium and pericardium. Against the background of protein depletion, fibrosis also progresses. This can lead to the clinic of specific pericarditis with myocarditis. From the side of the heart, the following deviations are detected:

• bradycardia (heart rate less than 60 per minute);
• muffled heart sounds;
• pain in the region of the heart, which does not depend on physical activity;
• decrease in systolic blood pressure, in the absence of changes in diastolic;
• expansion of all boundaries of the heart;
• decreased cardiac output;
• dilatation of chambers (especially of the left ventricle).

Heart pathology in hypothyroidism is also due to changes in the coronary arteries. A decrease in the concentration of the hormone triiodothyronine in the blood disrupts lipid metabolism in the body. The amount of triglycerides and cholesterol increases, which provokes the progression of atherosclerotic processes in the walls of blood vessels. As a consequence, the incidence of coronary heart disease and myocardial infarction increases in patients with hypothyroidism.

Treatment of hypothyroid heart begins with thyroid hormone replacement therapy. In addition, statins must be prescribed to lower cholesterol levels.