Thyroid Function and Heart

Imagine moving through mud. Because of the physical resistance caused by the mud, you have to use a lot of energy to get anywhere. It’s not hard, but it’s thick. It flows all around your limbs, making every movement twice as hard. Gummy, sticky, negatively-charged long linear polysaccharide compounds called glycosaminoglycans can pull 1000 times their weight in water into tissue clog your tissues. They function in different parts of the body, primarily in wound healing, and help build bone, cartilage, tendons, skin, and connective tissue. However, an accumulation will cause tissue damage. You feel clogged and swollen, but your heartbeat is accelerated, and you feel it in your head or when you’re lying down trying to relax.That is what the heart has to deal with if you are hypothyroid. With low thyroid hormone levels, every cell puts out less energy. T3 controls the electrical stimulus in the heart muscle. It also has a vasodilator effect on smooth muscle cells. You’ve probably heard about how important nitric oxide is for cardiovascular function and how it regulates vascular tone and blood flow. With low T3, nitric oxide releases to muscle cells less.T3 also controls the calcium entering heart muscle cells. The calcium passing into the cell gives muscle tissue cells their electrical charge; if there isn’t enough, the heart will slow down. The heart will contract more slowly. It will react less to the acetylcholine and norepinephrine stimulus, the neurotransmitters sent to the heart to increase or slow heart rate. Of course, since this affects blood flow and the speed at which oxygen reaches cells, this has a huge impact on your physiology.

It isn’t only the electrical signal for the heart rate that is profoundly affected by low T3. There is also a risk of endothelial dysfunction with hypothyroidism without a balance between vasoconstriction and vasodilation. Nitric Oxide regulates endothelial function. Low T3 reduces nitric oxide levels. Endothelial dysfunction is the cause of atherosclerosis due to platelets and monocyte adhesion, causing inflammation in the tissue and the scarring of smooth muscle cells. The cells lining the blood vessels become damaged, as can the myocardium and heart muscle tissues, due to the accumulation of collagen and glycosaminoglycans. This causes capillary permeability and swelling damage in muscle cells.

With this decreased ability of the heart to contract, the body has to compensate as best as it can. Oxygen has to get to essential tissues, such as brain and lung tissue, or you’d die. Your heart rate is up to 50% lower, so vascular resistance is increased up to 60% to make up for the lower heart rate. Heart conditions such as pericarditis, pericardial effusion, cardiac tamponade, when fluid collects in the pericardial sac, sinus bradycardia and tachycardia, and atrioventricular block are all caused by hypothyroidism. Low T3 levels decrease endothelial-mediated vasorelaxation and vascular compliance and elevate diastolic blood pressure. Diastolic contractions are 20% higher because the heart has to beat harder. It has to work harder. If the heart muscle is less elastic, stroke volume has to increase, which means high blood pressure and hypertension, to keep the blood flowing. There will be a narrowed pulse. You can even have angina-like pain in the heart itself when it’s trying desperately to do its job, with a decreased ability to contract and reduced muscle voltage. That lower voltage can cause arrhythmia and atrial fibrillation, two disorders in heart electricity.

There is a decrease in blood flow, and no tissues get the right amount of oxygen. Capillaries become weaker. Due to peripheral vascular resistance, spider veins may appear in the legs. Fluid will accumulate in tissues furthest away from the heart—like the lower legs and feet—and even around the pericardial pleura, causing pericardial effusion.

That’s why a person with hypothyroidism can feel so tired. This causes chronic fatigue, lethargy, muscle weakness, leg swelling, difficulty exercising, and shortness of breath. It almost feels like asthma. Your heart can be beating slowly but harder, so you hear it and feel it, often while lying down. Reduced blood flow causes cold hands and feet, frequently felt by people with low thyroid function.

People with low thyroid function are often prescribed beta-blockers and angiotensin inhibitors, but 40% of people with hypothyroidism have hypertension. The beta-blockers make thyroid function even worse. They also alter how the kidneys filter potassium and sodium, which affects kidney function and adrenal function. There are so many drugs prescribed to regulate heart rhythm for hypotension and hypertension. And off-label use for Klonopin, a potent benzodiazepine that is very addictive, is being used as a dopamine agonist to lower blood pressure. It might be a good idea to investigate thyroid function more closely, beyond the routine TSH test, because the thyroid-stimulating hormone does not respond to lower thyroid hormone levels in many tissues, most importantly the brain.

The slowed-down cardiovascular function on tests leads cardiologists, who often do not relate the changes in blood chemistry markers and electrocardiograms to thyroid function, to diagnose heart disease. High cholesterol used to be a diagnosis for hypothyroidism. I don’t mean 300 mg/dl by high cholesterol, which used the cut-off point until 1984. Both cholesterol and triglycerides can be high in hypothyroidism because low thyroid hormone promotes the clearance of LDL in the liver and the degradation of triglycerides into fatty acids that would be metabolized into energy if you were euthyroid.

Other blood markers that will be out of range due to low thyroid hormone levels, such as troponin, which is associated with heart tissue injury, can be high. Phosphatidylinositol 3-kinase (PI3K) and the serine/threonine-protein kinase, which are protective of endothelial tissue, will also come up low. Hypothyroidism increases clotting factors. Low T3 increases the D-dimer level and causes a hypercoagulable state. The D-dimer test will often be high and suggest increased blood clotting.

I’ve had several patients rushed to the hospital when these kinds of blood tests come back indicating possible cardiovascular irregularities. Even though it’s been known for a century that high cholesterol is associated with hypothyroidism cardiomyopathy, and known for three decades that T3 hormone regulates cardiac muscle output, cardiologists seldom test patients for hypothyroidism. One of my patients’ cardiologists stated that thyroid function had nothing to do with cardiovascular function.

Changes in cardiovascular function caused by hypothyroidism:

Hemodynamic effects of hypothyroidism and their effects on molecular mechanisms:

Decreased cardiac output=Endothelial dysfunction

Increased systemic vascular resistance=Decreased nitric oxide production.

Decreased arterial compliance=Decreased vascular smooth muscle relaxation.

Increased diastolic pressure= Decreased vascular smooth muscle relaxation.

Atherosclerosis=Decreased vascular smooth muscle relaxation.

Increased risk of coronary artery disease= Decreased vascular smooth muscle relaxation.