Both untreated hypothyroidism and thyrotoxicosis can lead to cardiovascular complications (complications involving the heart, arteries, and veins) or a worsening of risk factors for cardiovascular disease. The term heart disease generally refers to any type of heart trouble, including irregular or rapid heart rhythms; blockages of the blood supply to the heart muscle causing chest pain (angina) or a heart attack (myocardial infarction); or weakening of the pumping of the heart, causing congestive heart failure.
The term atherosclerotic cardiovascular disease (ASCVD) refers to fatty blockages of blood vessels anywhere in the body. When they occur in the coronary arteries that feed the heart muscle, they put you at risk for a heart attack. When ASCVD occurs in blood vessels in the brain, they put you at risk for having a stroke, in which the part of the brain fed by the blocked blood vessel dies. When ASCVD affects arteries that feed your arms or your legs, it causes peripheral vascular disease. In addition, some people have heart disease that may not be related to ASCVD that affects the way the heart beats. Normally, the heart beats at a regular rhythm of between ? fty and ninety beats per minute. Any disturbance of this rhythm is called an arrhythmia, and rapid rhythms are called tachyarrhythmias.
In thyroid patients who are otherwise healthy, these cardiovascular complications disappear or resolve as soon as you return to a euthyroid state, or normal thyroid function. In thyroid patients who have preexisting cardiovascular disease or who have risk factors for cardiovascular disease (obesity, smoking), untreated hypothyroidism or thyrotoxicosis can accelerate the worsening of cardiovascular problems. This section will brie?y summarize the range of heart problems that can be complicated by thyroid disease.
Heart Complications from Hypothyroidism
Hypothyroidism slows down the heart, causing a slow pulse called bradycardia. This might cause decreased exercise tolerance, shortness of breath, or a feeling of being winded when you try to exert yourself. Prolonged hypothyroidism will also lead to the accumulation of ?uids, called lymphedema, which can swell your hands and feet and mimic the type of edema seen with congestive heart failure.
Because your arteries require thyroid hormone to relax, hypothyroidism causes them to tense up, resulting in high blood pressure. People with chronically weakened hearts from underlying ASCVD may not be able to pump blood very easily through these constricted blood vessels, worsening congestive heart failure with ? uid accumulating in the lower limbs or in the lungs. Hypothyroid-induced edema can aggravate any existing congestive heart failure or might even be mistaken for congestive heart failure.
For most people with hypothyroidism, the most serious early complication is high blood pressure, which can increase the risk of a heart attack or stroke as well as congestive heart failure. Hypothyroidism also increases cholesterol levels, which can increase the development of blockages in arteries (atherosclerosis), likewise leading to increased risk of a heart attack or stroke as well as congestive heart failure.
Sometimes people are misdiagnosed with congestive heart failure when hypothyroidism is the problem.
Congestive Heart Failure
The term congestive heart failure means that the heart is weakened and not pumping well. This is usually caused by long-standing problems such as damaged heart valves, high blood pressure, damage to the heart muscle, or, rarely, congenital heart defects—a variety of heart defects that could have been present at birth.
Heart failure usually develops over a period of years. When people with heart failure become hypothyroid, the heart weakens further and this condition can worsen. In addition, since the blood vessels throughout the body require thyroid hormone to relax, hypothyroidism makes it more dif?cult to push blood through them, a condition called increased peripheral vascular resistance. This makes it even more dif? cult for the left ventricle to pump blood forward and worsens the heart failure.
In people with normal thyroid function, the heart enhances its pumping action by beating faster. In hypothyroidism, the heart beats much slower and cannot compensate for heart failure by beating faster. It is very unusual for hypothyroidism, on its own, to weaken the heart suf?ciently to cause heart failure. It’s important to look for primary heart problems and treat them in addition to treating the hypothyroidism. If you have underlying heart failure that predated hypothyroidism or was unveiled as a result of hypothyroidism, treatment with lifestyle changes, blood pressure and cholesterol-lowering medications, or possibly surgery may be necessary.
Hypertension
About 10 to 20 percent of people with hypothyroidism suffer from hypertension, or high blood pressure, which can lead to heart failure if severe and left untreated for long periods of time. It can also lead to a heart attack or stroke. In the general population, target blood pressure readings are less than 140 over 80 ( 140/80). Readings greater than 140/85 are considered too high, although readings of just under 144/88 are sometimes considered borderline in an otherwise healthy person. For the general population, 140/85 is “lecture time,” when your doctor will begin to counsel you about dietary and lifestyle habits. By 150/90, many people are prescribed an antihypertensive drug, which is designed to lower blood pressure.
In the absence of thyroid disease, it’s known that obesity, smoking, and a high-sodium diet can put you at risk for hypertension.
Genetic factors are very important; your risks for hypertension are much higher if it runs in your family and certain ethnic groups have higher risks. High blood pressure can also be caused by kidney disorders, which are prevalent in people with diabetes, or by pregnancy.
High blood pressure is treated in people with thyroid disease by a two-pronged approach, treating both problems—which may also involve lifestyle changes and antihypertensive medications. If your blood pressure returns to normal, you can discuss with your doctor whether you are able to come off of the medications.
High Cholesterol and Hypothyroidism
Hypothyroidism can increase cholesterol in people whose cholesterol levels would ordinarily be normal while euthyroid. If you have high cholesterol that predates your hypothyroidism, your already high cholesterol level can jump off the charts. High cholesterol is dangerous because the excess cholesterol in your blood can lead to narrowed arteries (ASCVD), which in turn can lead to a heart attack or stroke.
In the absence of hypothyroidism, saturated fat is often a culprit when it comes to high cholesterol, but the highest levels of cholesterol are due to genetic features affecting the creation or disposal of cholesterol in the liver. Familial hypercholesterolemia refers to a genetic cause for high cholesterol that does not respond adequately to diet modi? cation.
Hypothyroidism can increase the levels of LDL-cholesterol in the blood (the so-called “bad” cholesterol). The liver is the organ responsible for ridding the body of cholesterol as well as making it. Much of hypothyroidism’s effect is caused by increasing the absorption of cholesterol from bile (a substance made by the liver), preventing the usual loss of the body’s own cholesterol in the intestines. In addition, the hypothyroid liver seems unable to effectively clear this cholesterol, contributing to its increased levels. A few months after starting the appropriate dosage of levothyroxine, suf?cient to make your TSH level normal, the elevating effects of hypothyroidism on cholesterol levels should be gone. Of course, if you have underlying elevated cholesterol levels, you may still need to treat your high cholesterol by modifying your diet and taking cholesterol-lowering medications.
Heart Complications from Thyrotoxicosis
Even when people feel few other symptoms of thyrotoxicosis, they usually feel the heart symptoms. Thyrotoxicosis speeds up the heart rate by increasing the sensitivity of the heart to catecholamines (adrenaline and related hormones). In otherwise healthy people, this can lead to palpitations and tachycardia (fast pulse). In people with underlying cardiovascular disease or risk factors for cardiovascular disease, thyrotoxicosis can lead to atrial ?brillation and arrhythmias (abnormal heart rhythms). The stress placed on the heart can aggravate angina (chest pain) as well as a type of congestive heart failure called high-output congestive heart failure.
Palpitations and Racing Heart
The classic heart complications associated with thyrotoxicosis are a very fast pulse and heart palpitations. If you are hyperthyroid as a result of Graves’ disease, once your thyroid hormone levels are reduced to normal, these symptoms will disappear. Treatment with either antithyroid medication or beta-blockers can slow the heartbeat and prevent the consequences of a racing heart, such as heart failure or atrial ? brillation. Once thyroid function is restored to normal, you can usually stop taking beta-blockers.
Complications with Amiodarone
Amiodarone is a potent medicine used to treat heart rhythm disturbances. It is infamous for causing three different types of thyroid problems. This is partly because the amiodarone drug contains a large amount of iodine and partly because the amiodarone tends to stay inside the body for many months, even though you may stop taking it. It is also because some people have a reaction to the amiodarone in which it causes an in?ammation of the thyroid gland, releasing stored thyroid hormones. If you’re taking this drug, make sure your doctor checks your thyroid function.
Chest Pain (Angina)
Chest pain or discomfort due to coronary heart disease is called angina. People with underlying heart disease may have worsening of angina when they are thyrotoxic. The heart’s metabolism is increased by the excess thyroid hormone, increasing the oxygen and sugar demands of the muscle. The acceleration of the heart rate also places additional demands on the heart muscle. Partially blocked coronary arteries are unable to meet this increased demand for heart-feeding blood. The chest pain of angina (angina pectoris) is the sign that there is not enough blood feeding the heart. If left untreated, this condition can develop into a heart attack, in which part of the heart muscle dies, putting the person at risk of death if it is severe enough. Treatment consists of efforts to reduce the stress and demands put on the heart by using beta-blockers and to enhance the blood ? ow through the coronary arteries either by using drugs that expand their diameter or with a balloon catheter to reduce blockages.