Atrial fibrillation and Thyroid Relationship
The butterfly-shaped gland in your neck is of vital significance for our overall health and wellbeing. The function of thyroid influences other organs, systems, and processes in the body. At the same time, they have an impact on thyroid function which only confirms that everything in our body is connected.
For instance, problems affecting heart can have a lot to do with thyroid function and atrial fibrillation is a good example. To learn more about the relationship between atrial fibrillation and thyroid gland scroll down.
What is atrial fibrillation?
According to Mayo Clinc, Atrial fibrillation (AFib) is defined as an irregular and, often, a rapid heart rate that can lead to blood clots, stroke, heart failure, and other heart-related complications. According to the American Heart Association, about 2.7 million Americans are living with this condition[i]. By the year 2030, the number of people with AFib is estimated to reach 12.1 million[ii].
Atrial fibrillation affects atria or two upper chambers of the heart which disrupts blood flow to the ventricles or the lower chambers meaning blood circulation throughout your body is also impaired. When left ignored or unmanaged properly, atrial fibrillation can lead to death.
What is the cause of atrial fibrillation?
Before we can begin discussing the relationship between thyroid and atrial fibrillation it’s important to learn how we develop this problem in the first place. AFib occurs when atria and ventricles don't work together as they should due to impaired electrical signaling. Under normal circumstances upper and lower chambers contract at the same speed, but in persons with AFib they aren't synched up, and atria contract irregularly and quickly.
It would be difficult, or almost impossible in some situations, to pinpoint an exact cause of atrial fibrillation, but it usually occurs as a result of an underlying problem. People may develop AFib due to:
- Hypertension or high blood pressure
- Congestive heart failure
- Coronary artery disease
- Heart surgery
- Binge drinking
- Congenital heart defects
- Thyroid problems
Everyone can develop AFib, but some people are at a higher risk. Common risk factors for AFib include genetics, obesity, alcohol intake, hypertension, heart disease, and other chronic conditions.
What are the symptoms of atrial fibrillation?
Some people may not experience any symptoms at all which is exactly why AFib is considered a serious problem. However, those who do experience some symptoms may notice the following:
- Chest pain
- Heart palpitations, i.e. feeling like your heart is skipping a beat or beating too fast
- Shortness of breath
- Lightheadedness and dizziness
- Intolerance to exercise
Symptoms of AFib vary and may come and go depending on the severity of the condition.
Thyroid and atrial fibrillation
As mentioned in the introduction of this article, thyroid activity and heart function influence one another. The activity of this butterfly-shaped gland can influence the way your heart works and contribute to atrial fibrillation as one of many causes of this condition. But, is there any truth in those claims? Evidence says yes.
Selmer et al. carried out a study whose main objective was to examine the risk of atrial fibrillation in relation to whole spectrum thyroid function. For this purpose, they analyzed data from 586,460 adults who had their thyroid function evaluated for the first time and were without the history of AFib or problems affecting this gland. Their results revealed that the risk of atrial fibrillation was closely associated with the activity of the thyroid.
Relatively low risk was observed in cases of hypothyroidism, but the high risk was recorded in hyperthyroid patients[iii]. However, scientists still noted that the irregular function of the thyroid and impaired hormone levels can still elevate the likelihood of developing atrial fibrillation.
This isn’t the only study which confirmed the link between thyroid function and atrial fibrillation risk. For instance, Zhang et al. investigated the effects of different thyroid hormone levels ranging from hypo- to hyperthyroidism on atrial fibrillation. In this study, scientists used rats which were randomized either to hypothyroidism or hyperthyroidism group and results were interesting, to say the least. Findings revealed that hypothyroidism and hyperthyroidism produced opposite electrophysiological changes in heart rate and atrial effective refractory period, both conditions significantly enhanced the risk of atrial fibrillation. Hypothyroidism was associated with a 78% higher risk of AFib while hyperthyroidism increased the susceptibility of developing AFib by 67%.
Duration of AFib was longer in hypo- and hyperthyroidism cases compared to euthyroid. Scientists concluded that both thyroid conditions lead to elevated AFib vulnerability. In fact, normal thyroid hormones are required to maintain healthy cardiac electrophysiology and to prevent arrhythmia and atrial fibrillation[iv].
Hypothyroidism and atrial fibrillation
Now that we’ve established the close link between thyroid disorders and atrial fibrillation risk it’s time to take a closer look into the relationship between hypothyroidism and AFib. Studies show that the link between hypothyroidism and atrial fibrillation is less recognized. In fact, the relationship between the two conditions is poorly studied which is why the underlying mechanisms behind the development of AFib in low thyroid state remain unexplained[v].
The link between hypothyroidism and atrial fibrillation is tricky. While studies have confirmed its existence, at this point it is unknown how this relationship works or why AFib occurs in hypothyroid patients.
To make the matter worse, it also appears that overtreating hypothyroidism can increase the likelihood of developing this heart condition according to research carried out by Anderson et al. at the Intermountain Medical Center Heart Institute. While they knew hypothyroidism increased the risk of atrial fibrillation, they didn’t consider the higher risk of this condition within what's considered to be normal thyroid hormone level. Their findings show scientists may reconsider what they call normal concentration of thyroid hormones.
For the purpose of their study, scientists surveyed the electronic medical records of 174,914 patients who were treated at their hospital. Their fT4 (free T4) levels were recorded, and patients weren't receiving thyroid hormone replacement therapy.
Then, they took normal fT4 levels and divided them into four quartiles and analyzed their hospital records for current or potential AFib diagnosis. Patients in the highest fT4 quartile had a 40% increase in existing atrial fibrillation than patients in the lowest quartile. During the three-year follow-up period prevalence of newly developing AFib increased by 16% in patients within the highest fT4 quartile[vi].
This study raises a question whether treatment for hypothyroidism could put a patient at the risk of AFib as therapies are geared toward reaching a normal level of thyroid hormones which happens to lead to the risk of this heart condition in the long run. Overtreating hypothyroidism is definitely a subject worth exploring, but it also shows that patients should never modify their own drug intake and they always need to report any symptoms and changes in their condition to the healthcare provider.
Hyperthyroidism and atrial fibrillation
Hyperthyroidism is indicated by excessive levels of thyroid hormones, and it's associated with a number of symptoms which affect a patient's health and quality of life. Unlike hypothyroidism which is poorly studied in this context, the relationship between hyperthyroidism and atrial fibrillation is more widely explored. Studies show that both subclinical and overt hyperthyroidism increases the risk of atrial fibrillation.
Mechanisms of action associated with this relationship are numerous including the fact that high levels of thyroid hormones induce a hyperdynamic cardiovascular state which leads to faster heart rate, enhanced left ventricular systolic and diastolic function, and a higher prevalence of supraventricular tachyarrhythmias.
At the same time, hyperthyroidism elevates left atrial pressure and impairs ventricular relaxation which leads to increased resting heart rate and higher atrial ectopic activity. Additionally, evidence shows that heart rate effects are mediated by T3-based increases in systolic depolarization meaning higher levels of this hormone could make your heart beat faster. Another mechanism of action associated with the development of AFib in hyperthyroid patients suggests that thyroid hormones induce the occurrence of paroxysmal atrial fibrillation through the increase of triggered activity of pulmonary veins[vii].
Studies reveal that the effects of thyroid hormones on ion currents of atrial myocytes contribute to the development of AFib. Hyperthyroidism is associated with shortened action potential duration which leads to atrial fibrillation. An action potential is caused when ions cross the neuron membrane[viii].
How is atrial fibrillation treated?
The primary goals of the AFib treatment are to reset the rhythm or control the heart rate, prevent blood clots, and reduce the risk of stroke. The actual treatment is recommended by the doctor, and it may not be the same for every patient with atrial fibrillation. You see, the treatment approach depends on various factors including whether a patient has other heart-related problems, their age, weight, or whether they're taking medications for other conditions. Some medications may not work with drugs that control drug rhythm.
This only confirms why it's important to inform your doctor thoroughly about your condition and symptoms you experience, but also shows why it's crucial to adhere to the doctor’s advice.
In many cases, doctors are able to reset heart rhythm through a procedure called cardioversion. Some medications prescribed for the treatment of AFib include dofetilide (Tikosyn), flecainide, and others.
Of course, adequate management of atrial fibrillation requires treatment of an underlying condition too. For example, if a patient has hypothyroidism or hyperthyroidism, proper treatment of these conditions may also improve management of AFib.
Things you can do to manage atrial fibrillation
Men and women with atrial fibrillation have various options at their disposal to manage their condition and reduce the stroke risk. Like in many other cases a healthy lifestyle is vital here. Don’t be shy; ask your doctor everything you want to know about this condition.
The more you know, the better you'll understand, and you'll work harder to manage it properly. Simple lifestyle modifications go a long way. In addition to taking medications and treating underlying conditions (in this case hypo- or hyperthyroidism), other management methods include:
- Well-balanced diet – food you eat has a major impact on your health and heart function in particular. Instead of junk food opt for healthier foods, fruits, vegetables, nuts and seeds which deliver vitamins, minerals, and other nutrients important for heart health
- Limit caffeine intake – coffee, energy drinks, and other products containing caffeine act as stimulants and make your heart race even more
- Exercise and increase physical activity levels – people think they can’t exercise if they have AFib, but that’s not correct. You see, physical activity is crucial for heart health, but opt for moderate intensity. Avoid being sedentary
- Other tips include: manage stress, get enough sleep, lose weight, get support from loved ones, quit smoking and drinking alcohol, meditate, practice yoga
Atrial fibrillation is a potentially serious condition as it increases the risk of stroke. Both hypo- and hyperthyroidism are associated with atrial fibrillation, but the latter is more widely researched. Management of the underlying conditions in addition to a healthy lifestyle is important for the treatment of atrial fibrillation and reduced risk of stroke.
[i]. What is atrial fibrillation (AFib or AF)? American Heart Association https://www.heart.org/en/health-topics/atrial-fibrillation/what-is-atrial-fibrillation-afib-or-af
[ii] Colilla S, Crow A, Petkun W, et al. Estimates of current and future incidence and prevalence of atrial fibrillation in the US adult population. American Journal of Cardiology 2013 Oct 15;112(8):1142-7. Doi: 10.1016/j.amjcard.2013.05.063 https://www.ncbi.nlm.nih.gov/pubmed/23831166
[iii] Selmer C, Olesen JB, Hansen ML, et al. The spectrum of thyroid disease and risk of new-onset atrial fibrillation: a large population cohort study. The BMJ 2012;345:e7895. Doi: 10.1136/bmj.e7895 https://www.bmj.com/content/345/bmj.e7895
[iv] Zhang Y, Dedkov EI, Teplitsky D, et al. Both hypothyroidism and hyperthyroidism increase atrial fibrillation inducibility in rats. Circulation 2013 Oct;6(5):952-9. Doi: 10.1161/CIRCEP.113.000502 https://www.ahajournals.org/doi/10.1161/CIRCEP.113.000502
[v] Patel DK, Gujral JS. Atrial fibrillation in hypothyroidism. Journal, Indian Academy of Clinical Medicine 2009 Jul-Sep;10(3):140-2 http://medind.nic.in/jac/t09/i3/jact09i3p140.pdf
[vi] Overtreating patients for hypothyroidism could raise their risk of stroke, study finds. Medical Xpress 2018 Nov https://medicalxpress.com/news/2018-11-overtreating-patients-hypothyroidism.html
[vii] Bielecka-Dabrowa A, Mikhailidis DP, Rysz J, Banach M. The mechanisms of atrial fibrillation in hyperthyroidism. Thyroid Research 2009 Apr;2:4. Doi: 10.1186/1756-6614-2-4 https://thyroidresearchjournal.biomedcentral.com/articles/10.1186/1756-6614-2-4#Sec3
[viii] N, J., & Francis, J. (2005). Atrial fibrillation and hyperthyroidism. Indian pacing and electrophysiology journal, 5(4), 305-11. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1431605/
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