Understanding the Link Between Thyroid Health and Heart Disease

Palpitations? Shortness of breath? Fatigue and weakness?  It might surprise you to learn that your thyroid health could be a contributing factor in your cardiovascular health. 

Hello, everyone! I'm Dana Gibbs MD, an ENT doctor and hormone expert with a passion for making the mysteries of thyroid health understandable.

The thyroid, a small but mighty gland in our neck, plays a crucial role in regulating our body's metabolism and protein synthesis. This is done by the secretion of thyroid hormones (THs), namely triiodothyronine (T3) and thyroxine (T4). These hormones circulate in the blood and go to all our body tissues where they bind and activate by the means of Thyroid Receptors that are present on all our body cells. 

If you are interested in learning more about the basic function of the thyroid, you can check out my earlier blog post blog at https://www.danagibbsmd.com/blog/thyroid-101.

Today, let's check out the interplay between thyroid function and cardiovascular health, particularly the often-overlooked association between hyperthyroidism and heart failure. Before we go there, it’s important to understand that the action of thyroid hormone at these Thyroid Receptors can be underactive (hypothyroid) and overactive (hyper-thyroidism). These two opposites can occur for a variety of reasons and in a variety of ways, but the most common reasons are autoimmune diseases - Hashimoto’s disease, and Graves disease.  These I have explored in other episodes, but the bottom line is that both of these diseases can cause either hyperthyroidism or hypothyroidism. We are going to start with the less common Hyperthyroidism today. Hyperthyroidism can also be caused by taking too much thyroid hormone. Occasionally people will purposely take too much because they like the buzzy energy they tend to feel. But we’re going to look at why that’s actually a terrible idea.

The Genomic and Non-Genomic Pathways

T3 is the main hormone that influences cardiac function. It does this in 2 ways - The genomic pathway, the major pathway - involves T3 binding to specific elements in the DNA of all our body cells called target genes, and activating the production of proteins needed for various healthy body functions and cell growth and repair.  The second pathway, the  non-genomic pathway, influences changes in function of cells' ability to produce energy, and particularly today we’re talking about myocytes,  heart muscle cells,  which provide the heart’s pumping capability.

Hyperthyroidism and Cardiac Dysfunction

Research suggests that the combined effects of both these pathways are responsible for heart problems in the  hyperthyroid state, affecting the elderly population more than younger people. And it is pretty common: maybe as much as 5% of the population will have hyperthyroidism at some point in their lives.

 Tachycardia and Atrial Fibrillation:

Thyroid hormone (particularly T3, the active form of thyroid hormone) overall speeds up the rate of the heartbeat signaling activity, resulting in a fast and frequently irregular heartbeat. The most common cardiac phenomenon observed in hyperthyroidism is tachycardia, sinus tachycardia as the most common, but frequently presenting as an irregularly irregular rhythm known as Atrial Fibrillation. Prolonged tachyarrhythmia can potentially lead to heart failure, emphasizing the importance of timely diagnosis and management. Atrial fibrillation, though rare in hypothyroidism, is consistently associated with high levels of thyroid hormone, making it crucial for patients and healthcare providers to be vigilant. Luckily patients with hyperthyroidism don’t often go unrecognized due to the other symptoms of hyperthyroidism, that include heat intolerance, sweating, rapid weight loss, and anxiety. 

And while  atrial fibrillation and tachycardia (rapid heart rate) are well known effects of overactive thyroid, there are several more that are less well known and more ominous. 

Cardiovascular Effects of Hyperthyroidism:

Studies show that hyperthyroidism triggers a cascade of cardiovascular changes, including reduced peripheral vascular resistance, and increased cardiac output. Let’s talk a little more about what these things mean and why they happen. 

First, T3 is thought to reduce the effect of Angiotensin 2. Angiotensin II is another neurochemical hormone in our bodies that helps us maintain our blood pressure in the presence of dehydration, by stimulating the retention of salt and water by our kidneys, and by increasing norepinephrine.  Norepinephrine, like Epinephrine, is responsible for increasing the strength and speed of heart contractions. So, initially, less blood volume, and less strength and speed of heart contractions, lower blood pressure.

The Physiological Effects on Blood Vessels

T3 also promotes blood vessel relaxation by stimulating nitric oxide production. Nitric oxide promotes blood vessel relaxation. So the more T3 there is, the lower the diastolic blood pressure goes. That’s the lower number in your blood pressure reading, measured while the heart is relaxing in between beats. That actually sounds good, right? Relaxation should lower blood pressure. When the blood vessels in our bodies relax, total peripheral resistance is reduced (the pipes so to speak, are bigger than they were before. Then 2 things have to happen: the heart has to pump faster and higher volume to get enough blood out to the tissues, and eventually the volume of blood will need to go up to restore balance. If it doesn’t go up, it can result in dizziness and even fainting. 

The thyroid hormone effects on Cardiovascular Physiology

Beyond vasculature, THs also enhance myocardial contractility , by a non-genomic effect on the ability to handle Calcium more efficiently this means stronger beats. You get what’s called a widened pulse pressure (that's the difference between the top and bottom numbers in the blood pressure reading), since there is decreased total peripheral resistance, the heart needs to pump more blood per beat.  And more blood volume is needed because the blood vessels are dilated. So now we actually produce more angiotensin. The heart is then beating faster and stronger. and paradoxically we now get even more vasodilation. This vicious cycle may then lead to development of “high output” heart failure.

Also in order to handle the higher need for blood flow, TH enhances new coronary blood vessel growth , and hypertrophy (enlargement) of the myocardium. This also sounds good, except that when the heart muscle enlarges, it enlarges inward as well as outward. This makes the volume pumped with each beat less. So the heart needs to go even faster.  The structural remodeling also promotes electrical conduction defects which show up as irregular heartbeats. When this is prolonged it can also lead to heart failure.

Hyperthyroidism and Heart Failure:

Approximately 6% of patients with hyperthyroidism initially present with heart failure, with half experiencing left ventricular dysfunction. Most of these are due to the extremely rapid heart rate reducing the efficiency of the pumping ability of the heart. 

Effective management involves converting patients to a euthyroid state with thyroid blocking medications, controlling heart rate with beta blockers, and initiating diuretics. Studies have consistently shown that this regimen leads to improved patient outcomes, emphasizing the importance of early diagnosis and intervention. 

The longer the hyperthyroidism has been present, the higher the chance of long term heart damage, so if you have symptoms of elevated thyroid function, it’s important to make sure that is treated correctly.

Key points:

Although the interaction between hyperthyroidism and heart problems is complex, by Understanding the signs and symptoms and getting them diagnosed and treated, we can minimize the impact of hyperthyroid-related cardiovascular disorders. We will go over the impact of hypothyroidism on a future episode. 

So that's it for now.  I'm Dana Gibbs MD. I'm an integrated physician in North Texas. I help people address thyroid and other hormone imbalances. And if you're a thyroid or chronic fatigue suffer in North Texas and you want a caring doctor to help you resolve your exhaustion, joint and muscle aches, poor sleep issues and weight gain, come sign up for a new patient evaluation with me now. Stay informed, stay proactive, and prioritize your heart health!

References: 

Khan, R., Sikanderkhel, S., Gui, J., Adeniyi, A.-R., O’Dell, K., Erickson, M., Malpartida, J., Mufti, Z., Khan, T., Mufti, H., Al-Adwan, S. A., Alvarez, D., Davis, J., Pendley, J., & Patel, D. (2020, April). Thyroid and cardiovascular disease: A focused review on the impact of hyperthyroidism in heart failure. Cardiology research. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7092768/