Tachycardia and Thyroid Health

Before I was diagnosed with hyperthyroidism, and eventually Graves’ disease, I realized something was wrong one day when I measured my blood pressure and discovered that I had an elevated resting heart rate (my blood pressure was fine).  An elevation in the resting heart rate is known as tachycardia, and this is one of the classic symptoms of hyperthyroidism.  However, there can be other reasons why people can have an elevated heart rate, and so I decided to put together a blog post where I will discuss some of the common causes of tachycardia, as well as some of the different treatment options available.

You might wonder how high the resting heart rate needs to be before it’s labeled as tachycardia.  Most sources consider a resting heart rate over 100 beats per minute (BPM) as being tachycardia.  While this may be true, I definitely prefer to see the resting heart rate less than 80 BPM, and I would be concerned with a resting heart rate of 90 BPM or greater, and ideally you want a resting heart rate in the 50s or 60s, although the low 70s is still acceptable.

So while the literature considers a “normal” resting heart rate anywhere between 60-100 BPM, I consider a consistent resting heart rate of over 80 BPM to be elevated.  And by “consistent” I mean that when you measure your heart rate multiple times across a period of days or weeks it is over 80 BPM the majority of the time.  This doesn’t mean that everyone who has a consistent resting heart rate over 80 BPM has one of the conditions I’ll be mentioning in this post, as they might simply by physically unfit.  The reason for this is because a lower resting heart rate usually indicates a higher level of cardiovascular fitness.

How Do You Measure Your Resting Heart Rate?

When I had hyperthyroidism I took the herbs bugleweed and motherwort, and the way I knew these herbs were working was by monitoring my resting pulse rate (and of course eventually I did follow-up blood tests).  While I’m sure many people reading this know how to do this, others don’t, and so I figured I’d include a few videos demonstrating how to measure your resting pulse rate.  Of course you can also invest in an automated device that measures your resting heart rate.  There are some phone apps that do this too, although I don’t trust the accuracy of them.

https://www.youtube.com/watch?v=oAjnlDZH9H8

https://www.youtube.com/watch?v=AHHr8qNU9QY

Different Types of Tachycardia

I’d like to briefly mention three different types of tachycardia:

1. Atrial or Supraventricular Tachycardia (SVT).  This involves an irregular heart rhythm (arrhythmia) that starts in the upper chambers of the heart.

2. Sinus Tachycardia.  Sinus tachycardia is a regular cardiac rhythm in which the heart beats faster than normal and results in an increase in cardiac output (1).  This is the type of tachycardia most commonly associated with hyperthyroidism.

3. Ventricular Tachycardia.  This involves an arrhythmia that starts in the lower chambers of the heart.

Causes of Tachycardia

Let’s go ahead and discuss some of the different causes of tachycardia:

Hyperthyroidism.  Although this isn’t the most common cause of tachycardia, I’m listing it first simply because this website focuses on helping people with thyroid and autoimmune thyroid conditions.  And most of my patients with hyperthyroidism have an elevated resting heart rate, although not everyone experiences a heart rate greater than 100 BPM.

Elevated cortisol levels.  This is another potential cause of an elevated resting heart rate, although once again, it’s uncommon for this to cause a heart rate greater than 100 BPM.  As a result, in the literature it’s not considered to be a common cause of tachycardia, but I put this towards the top because it’s another common reason why someone might have a resting heart rate between 80 to 100 BPM, although sometimes it can cause the resting heart rate to exceed 100 BPM.

Hypoglycemia.  I’ve written articles on hypoglycemia and thyroid health, and this can be a cause of tachycardia.

Dehydration.  I’m not sure if mild dehydration will result in tachycardia, but if someone has moderate to severe dehydration then in order to maintain cardiac output in the setting of intravascular depletion, heart rate will increase (2).

Hyperkalemia.  This is elevated potassium levels, and can be caused by renal failure, excessive exercise, metabolic acidosis, insulin deficiency, medication-induced, and increased intake of potassium (3).

Hypomagnesemia.  Low magnesium levels can also cause tachycardia in some cases.  And many people are deficient in magnesium.

Hypocalcemia.  Low calcium levels are another potential cause of tachycardia.

Infections.  This is another common cause of an elevated heart rate.  In the literature, sepsis is listed as a potential cause of tachycardia, but the infection doesn’t need to be life-threatening to cause an elevated resting heart rate.  In fact, if your heart rate seems to be normal during the day but becomes elevated at night while you’re sleeping, it very well might be caused by a chronic infection (although there can be other causes).

Anemia.  There are different types of anemia, including microcytic, normocytic, and macrocytic.  I’m not going to get into detail about the different types here, but just keep in mind that this condition can be easily diagnosed through a complete blood count, as a low hemoglobin or hematocrit is a sign of anemia.

Caffeine.  Of course many people drink coffee, but there are other sources of caffeine (i.e. green tea, chocolate), and it’s important to keep in mind that some people are slow metabolizers of caffeine, and this might make someone more likely to have an elevated resting heart rate.

Certain medications.  Some of the medications that can potentially cause tachycardia include Albuterol, amphetamines, antihistamines, Clozapine, Dobutamine, Ephedrine, levothyroxine, Theophylline, and tricyclic antidepressants.  Since my focus is on thyroid health I should highlight levothyroxine, which is synthetic thyroid hormone taken by people with hypothyroidism.  Any type of thyroid hormone replacement can result in tachycardia if the dosage is too high.

Pregnancy.  Being pregnant will result in many physiologic changes, including an increased resting heart rate, cardiac output, and vascular volume (4).

Hypoxia.  This occurs when the tissues do not receive the necessary amount of oxygen to support their metabolic demand.

Postural orthostatic tachycardia syndrome (POTS).  This is a potentially chronic debilitating condition involving the autonomic nervous system, and it is characterized by symptoms of lightheadedness, fatigue, palpitations, pre-syncope, sleep disturbances, cognitive impairment and brain fog in conjunction with an exaggerated increase in heart rate when upright, despite maintenance of a normal blood pressure (5).

Potential Consequences of Unmanaged Tachycardia

Unmanaged tachycardia can have numerous health consequences.  In some cases it can lead to myocardial ischemia, low blood pressure, low cardiac output, peripheral hypoperfusion (reduced amount of blood flow), tachycardia-mediated cardiomyopathy (TMC), cardiac arrest and even death (6).  The good news is that most of these conditions are partially or completely reversible, including TMC (6), although the goal should be to prevent these conditions from developing in the first place.

Management of Tachycardia:

Obviously the goal should be to address the underlying cause of the tachycardia.  But while doing this it can be important to take medication or herbs to manage the symptoms.  So for example, if someone has tachycardia caused by hyperthyroidism it’s important to do things to lower the resting heart rate while addressing the cause of the problem.  That being said, let’s look at some of the things that can be done to manage the tachycardia while the underlying cause is being addressed

1. Beta blockers.  Beta blockers work by binding to beta-adrenergic receptors, and this is how they get the name “beta” blockers.  These receptors play an important role in the regulation of heart function.  I’ve written a separate article on beta blockers that discusses how they work, the different types, and some common side effects.

2. Angiotensin-converting enzyme (ACE) inhibitors.  Although some of the research I did on the management of tachycardia mentioned ACE inhibitors, these are mainly used to help with high blood pressure.  Angiotensin II is a substance that causes the blood vessels to narrow and constrict, which can lead to high blood pressure.  ACE inhibitors work by preventing antiotensin I from converting into angiotensin II.

3. Antithyroid medication.  This of course is specific for those with hyperthyroidism, as it lowers the thyroid hormone levels, which in turn can result in a decrease in the resting heart rate.

4. Motherwort.  This herb is commonly used to decrease the cardiac symptoms associated with hyperthyroidism, although it can be used when someone has tachycardia due to other causes.  Although motherwort isn’t as potent as a prescription beta blocker, some sources show that this herb has a blocking effect on beta adrenergic receptors.

5. Hawthorn.  Like motherwort, this is another herb that can help to decrease the cardiac symptoms associated with hyperthyroidism.  According to the research, hawthorn doesn’t block the beta-adrenergic receptors (7) (8).

6. Bugleweed.  Just as is the case with antithyroid medication, bugleweed can lower the resting heart rate by lowering thyroid hormone levels.

Have You Experienced Tachycardia?

If you currently have tachycardia, or had it in the past due to hyperthyroidism or another health condition, please feel free to share your experience in the comments section below.  I’ll be happy to start, as when I was dealing with hyperthyroidism I had a resting heart rate that ranged between 90 and 110 BPM, and I used both bugleweed and motherwort to manage my symptoms while addressing the cause of my condition.