Hypothyroidism and hyperthyroidism can cause arrhythmia, heart failure, and difficulty breathing in people without heart disease.
The thyroid is a small, butterfly-shaped gland in the back of the throat that performs many important functions in the body. Thyroid disease can cause heart problems in people who do not have heart disease. It also worsens heart symptoms and accelerates heart problems in people with heart disease.
Hypothyroidism
Hypothyroidism is a condition in which the thyroid gland is underactive and does not produce enough thyroid hormones. Without enough of this hormone, the heart and blood vessels cannot function normally. Reduced thyroid hormone levels cause the heart muscle to pump blood less strongly and weaken over time.
The heart muscle’s inability to fully relax after each heartbeat can cause diastolic dysfunction or stiffening of the heart’s pumping chamber, leading to heart failure. Hypothyroidism also causes blood vessels to stiffen and high blood pressure.
Below are heart symptoms that may occur in people with hypothyroidism:
Swelling (edema): Edema often occurs as a result of worsening heart failure. Hypothyroidism can cause a type of edema called myxedema, caused by a buildup of abnormal proteins and other molecules in the fluid surrounding the body’s cells.
Heart arrhythmia: Hypothyroidism can worsen premature and irregular heartbeat, atrial fibrillation.
Heart failure: People with mild heart disease if hypothyroidism can also cause heart failure.
High diastolic blood pressure: Arteries develop stiffness in hypothyroidism, causing diastolic blood pressure to increase.
Shortness of breath: Dyspnea on exertion and poor mobility in patients with hypothyroidism are often due to weak skeletal muscles. In people with heart disease, the cause may be worsening heart failure.
Slow heart rate: Heart rate is regulated by thyroid hormones. When not enough thyroid hormone is produced, the heart rate is often 10-20 beats per minute slower than normal, especially in patients with heart disease.
Coronary artery disease gets worse: An increase in bad cholesterol (LDL) and C-reactive protein (an inflammatory protein) in hypothyroidism can accelerate symptoms of coronary artery disease.
Hyperthyroidism
Hyperthyroidism causes the body to produce too much thyroid hormone, causing the heart muscle to work harder and the heart rate to increase. Excess thyroid hormone increases the force of contraction of the heart muscle and increases the amount of oxygen the heart needs. For people with heart disease, an overactive thyroid can seriously affect health.
Heart symptoms that may occur in people with hyperthyroidism are as follows:
Fast heart beat: Undetected hyperthyroidism is a common cause of increased heart rate at rest or light exertion.
Heart arrhythmia: For people with heart disease, hyperthyroidism causes many arrhythmias such as premature ventricular complexes, tachycardia and atrial fibrillation.
Heart failure: Hyperthyroidism can cause heart failure but it is rare. People with pre-existing heart disease are at higher risk of heart failure due to hyperthyroidism.
High systolic blood pressure: Hyperthyroidism causes the heart to contract strongly, leading to increased systolic blood pressure or increased pressure in blood vessels when the heart contracts more.
Shortness of breath: Shortness of breath may be due to skeletal muscle weakness related to hyperthyroidism or to worsening heart failure.
Angina pectoris gets worse: Patients with coronary artery disease often have more severe symptoms with increased thyroid hormone production. These often include increased angina and heart attacks.