Cardiac Effects of Thyroid Disease

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Cardiac Effects of Thyroid Disease

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The thyroid, a small gland located in the neck, is responsible for

modulating many vital bodily functions. By producing just the right amount of

thyroid

hormone, it helps to regulate the body's metabolism (specifically, how much

oxygen and energy the body uses,) as well as digestive function, muscle

function, and the normal integrity of the skin. In fact, the thyroid has at

least

some effect on every organ in the body - including the heart.

 

For people with almost any type of heart disease, disorders of the thyroid

gland can worsen old cardiac symptoms or cause new ones, and can accelerate

the underlying heart problem. Even worse, doctors frequently forget to think

about the thyroid when cardiac symptoms are worsening, and if they don't think

of it they will miss it. Often, it's the savvy patient who reminds the doctor

that thyroid function ought to be checked. This is why it is useful for

those with heart disease to know a little about the cardiac effects of thyroid

disease.

 

Disorders of the thyroid gland usually involve either the failure to produce

enough thyroid hormone (hypothyroidism) or the production of too much

(hyperthyroidism). Both types of thyroid disorders are common.

 

Hypothyroidism and the heart

 

Thyroid hormone is very important for normal cardiovascular function, so

when not enough thyroid hormone is present neither the heart nor the blood

vessels function normally. In hypothyroidism the heart muscle is weakened in

both

its contraction phase, and also its relaxation phase. This means that the

heart cannot pump as vigorously as it should, and the amount of blood it ejects

with each heart beat is reduced. In addition, because the heart muscle does

not relax normally in between heart beats, a potentially serious condition

called diastolic dysfunction may result. (Read about diastolic dysfunction here

_http://heartdisease.about.com/od/livingwithheartfailure/a/diastolic_HF.htm_

(http://heartdisease.about.com/od/livingwithheartfailure/a/diastolic_HF.htm)

). Furthermore, hypothyroidism reduces the amount of nitric oxide in the

lining of the blood vessels, causing them to stiffen.

 

Cardiac symptoms of hypothyroidism

 

Cardiac symptoms can be seen in anybody with hypothyroidism, but are

especially likely in an individual who already has underlying heart disease.

 

Common symptoms include:

 

-- Shortness of breath on exertion and poor exercise tolerance. These

symptoms, in most patients with hypothyroidism, are due to weakness in the

skeletal

muscles; but in patients with heart disease, the symptoms may be due to

worsening heart failure.

 

-- Slow heart rate (bradycardia.) The heart rate is modulated by thyroid

hormone, so that in hypothyroidism the heart rate is typically 10 - 20 beats

per

minute slower than normal. Especially in patients who also have heart

disease, however, hypothyroidism may worsen the tendency for premature beats

(such

as PVCs) and even tachycardias such as atrial fibrillation.

 

-- Diastolic hypertension. One might think that, because a lack of thyroid

hormone slows down the metabolism, people with hypothyroidism might suffer

from low blood pressure. Usually the opposite is true - the arteries are

stiffer

in hypothyroidism, which causes the diastolic blood pressure to rise.

 

-- Worsening of heart failure, or the new onset of heart failure.

Hypothyroidism can make well-controlled heart failure worsen, and can produce

heart

failure for the first time in patients with relatively mild underlying heart

disease.

 

-- Edema (swelling.) Swelling can occur as a result of worsening heart

failure. In addition, hypothyroidism itself can produce a type of edema called

myxedema, caused by an accumulation of abnormal proteins and other molecules in

the interstitial fluid (fluid external to the body's cells.)

 

-- Worsening of coronary artery disease. While the reduction in thyroid

hormone can actually make angina less frequent in patients who have angina, the

increase in LDL cholesterol(bad cholesterol) and in C-reactive proteinseen

with hypothyroidism can accelerate any underlying coronary artery disease.

 

Hypothyroidism can be an extremely subtle condition, and often occurs

without the typical, constellation of " textbook " symptoms doctors usually

expect.

It also occurs far more commonly than most doctors realize. So if you have

anyof these symptoms and your doctor does not have a ready or convincing

explanation for them, especially if you already have heart disease of any type,

ask

your doctor to measure thyroid hormone levels.

 

Treatment of hypothyroidism

 

The treatment of hypothyroidism can be a lot trickier than most doctors

think, and there are many considerations patients ought to take into account.

If

you have hypothyroidism, I urge you to read about its treatment here

_http://thyroid.about.com/_ (http://thyroid.about.com/) .

 

Next page: Hyperthyroidism and the heart

Cardiac Effects of Thyroid Disease - page 2

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_

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Hyperthyroidism and the heart

 

In hyperthyroidism, caused by the overproduction of thyroid hormone, the

heart muscle is " whipped " like a horse, and for a person with heart disease

it's

like whipping a tired horse.. Thyroid hormone increases the force of

contraction of, and the amount of oxygen demanded by, the heart muscle. It also

increases the heart rate. For these reasons the work of the heart is greatly

increased in hyperthyroidism. Hyperthyroidism increases the amount of nitric

oxide in the lining of the blood vessels, causing them to dilate and become

less

stiff.

 

Cardiac symptoms of hyperthyroidism

 

Cardiac symptoms can be seen in anybody with hyperthyroidism, but can be

particularly dangerous in people with underlying heart disease. Common symptoms

include:

 

-- Fast heart rate (tachycardia) and palpitationspalpitations. Occult

hyperthyroidism is a common cause of an increased heart rate at rest and with

mild

exertion. Hyperthyroidism should always be ruled out with blood tests before

making the diagnosis of Inappropriate Sinus Tachycardia. Especially in

patients with underlying heart disease, hyperthyroidism can also produce a host

of

other arrhythmias such as PVCs, ventricular tachycardia, and especially

atrial fibrillation. Indeed, it is important to rule out hyperthyroidism in a

patient with atrial fibrillation and no clear underlying cause.

 

-- Systolic hypertension. The forceful cardiac contraction increases the

systolic blood pressure, though the increased relaxation in the blood vessels

reduces the diastolic blood pressure.

 

-- Shortness of breath on exertion. This can be due to the skeletal muscle

weakness cause by hyperthyroidism, or to a worsening in heart failure.

 

-- Heart failure. Hyperthyroidism itself can produce heart failure, but this

condition is relatively rare. On the other hand, if pre-existing heart

disease is present, worsening of heart failure with hyperthyroidism is common,

and

can be extremely difficult to treat.

 

-- Worsening angina. Patients with coronary artery disease often experience

a marked worsening in symptoms with hyperthyroidism. These can include an

increase in chest pain (angina) or even a heart attack.

 

As with hypothyroidism, hyperthyroidism can be present - and often is -

without the classic, textbook symptoms. So patients with any of these cardiac

symptoms that cannot otherwise be readily explained should have thyroid

function

measured. Furthermore, sometimes a " mild " hyperthyroidism can exist in which

thyroid blood tests can be misinterpreted. In these cases thyroid hormone

levels themselves are normal, but the level of thyroid stimulating hormone (TSH

- a hormone excreted by the pituitary gland that regulates the thyroid gland)

is low. A low TSH indicates hyperthyroidism, despite " normal " thyroid

hormone levels. This pattern of thyroid blood tests especially ought to be

sought

in all patients displaying any of the above symptoms with no clear reason for

them.

 

Treating hyperthyroidism

 

The " best " way of treating hyperthyroidism is controversial. In the U.S.,

most doctors immediately opt for ablating the overactive thyroid gland with

radioactive iodine, then giving the patient thyroid hormone pills since the

thyroid gland is no longer functional. This method is certainly " easiest " for

the

doctors, but often patients are left feeling chronically abnormal. Using

drugs to partially suppress the thyroid gland - in the U. S., Tapazole or PTU -

creates somewhat more of a long-term management issue for doctors, but may

lead to ultimately happier patients.

 

I urge patients contemplating therapy for hyperthyroidism to read Mary

Shomon's book, Living Well With Hyperthyroidism, to get an objective viewpoint

on

ALL the options for therapy - especially before opting for an irreversible

treatment like radioactive iodine therapy.

 

Also, whether you have hyperthyroidism or hypothyroidism, please spend some

time on Mary's thyroid website at About.com; the advice and support you'll

find there are excellent.

 

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