Inappropriate Sinus Tachycardia Symptoms and Treatment

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Inappropriate sinus tachycardia (IST) is a condition in which a person's heart rate at rest and during exertion is abnormally elevated for no apparent reason.

People with IST also experience heart palpitations, fatigue, lightheadedness, or exercise intolerance. IST symptoms can be debilitating and mimic conditions like anemia, hyperthyroidism, and side effects of medication. It is diagnosed after ruling out other causes.

IST is treated with lifestyle changes, avoiding triggers (like alcohol, caffeine, and stress), and medication to slow your heart rate.

This article discusses inappropriate sinus tachycardia. It explains the common symptoms and possible causes of IST, how it is diagnosed, and the treatment options available.

What Is Inappropriate Sinus Tachycardia?

Tachycardia is a medical term for a fast heartbeat. Inappropriate means it occurs outside of situations that would normally cause a rapid heart rate. Sinus refers to the sinus node, the cardiac structure that controls the normal heart rhythm.

Inappropriate sinus tachycardia syndrome is defined medically as:

  • A sinus heart rate greater than 100 beats per minute (bpm) at rest, with an average 24-hour heart rate greater than 90 bpm
  • Accompanied by uncomfortable symptoms such as dizziness, fatigue, and heart palpitations (a sensation that your heart is racing or pounding)
  • Cannot be explained by physiological demands
  • Occurs at rest or with minimal exertion
  • Is not related to exercise or recovery after exercise 
  • Other causes of tachycardia ruled out

Verywell / Lara Antal

Symptoms of Sinus Tachycardia

The primary symptom of IST is an elevated resting heart rate. A normal resting heart rate typically varies from 60 to 100 bpm. With IST, the heart rate can exceed 100 bpm at rest and averages above 90 bpm on a 24-hour monitor.

Heart Rates in Inappropriate Sinus Tachycardia
  Resting Sleep Exertion
Beats per Minute 100 or more 80-90 140-150

An elevated heart rate is just one aspect of inappropriate sinus tachycardia, however. Additional uncomfortable and sometimes debilitating symptoms are what differentiates IST from regular tachycardia.

Other symptoms of inappropriate sinus tachycardia include:

  • Chest pain
  • Dizziness
  • Dyspnea (shortness of breath)
  • Exercise intolerance
  • Fainting
  • Fatigue
  • Heart palpitations
  • Lightheadedness
  • Weakness

These IST symptoms are often anxiety-producing, disabling, and interfere with your quality of life. An estimated 90% of people with IST experience heart palpitations.

See Your Healthcare Provider

Symptoms of inappropriate sinus tachycardia warrant medical attention. While IST is not usually dangerous, symptoms like chest pain, heart palpitations, and shortness of breath can indicate a more serious condition and should be evaluated.

Causes of Sinus Tachycardia

The main cause of IST is not yet known. Experts theorize that people who have IST may be hypersensitive to adrenaline—a little bit of adrenaline causes a marked rise in heart rate. This may be due to:

  • Neurohormonal dysregulation, a problem in which the neuroendocrine system is not properly regulating the heart rate
  • Dysautonomia, a disorder of the autonomic nervous system, which manages the "unconscious" bodily functions, such as digestion, breathing, and heart rate
  • Structural changes within the sinus node of the heart

While anyone can develop IST, it is four times more common in people assigned female at birth. IST is often diagnosed in people in their 30s or 40s, though it can affect older adults as well.

Studies show IST often first occurs after a precipitating event. Common triggers include:

  • Anxiety
  • Depression
  • Extreme emotional stress
  • Infectious illness
  • Pregnancy

Diagnosing Inappropriate Sinus Tachycardia

IST is what is known as a diagnosis of exclusion. It is diagnosed only after ruling out other potential causes of an abnormal sinus tachycardia, such as:

These can often be ruled out with a physical examination, blood tests to look for other causes of tachycardia, and urine tests. Other tests used to exclude other conditions and diagnose IST include:

  • A 12-lead electrocardiogram (EKG) to analyze the heart’s electrical rhythm and the type of tachycardia
  • A 24-hour Holter monitor to continuously observe heart rhythms over a longer period of time
  • Chest X-ray to view the heart and lungs
  • Echocardiogram, an imaging scan to assess the size, structure, and pumping ability of the heart
  • Exercise test to assess the severity of symptoms
  • Tilt table test to rule out POTS 

Other tests sometimes used to evaluate cardiac autonomic responses include:

  • Baroreflex sensitivity
  • Cold face test, also known as diving test
  • Heart rate variability
  • Valsalva

However, these tests are not routinely used because of unproven clinical benefits.

A Commonly Missed Diagnosis

IST was first recognized as a syndrome in 1979 and has only been accepted as a true medical diagnosis since the late 1980s. Still, some physicians are unfamiliar with it and may misdiagnose it as anxiety.

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Treating Inappropriate Sinus Tachycardia

IST is a difficult condition to treat in part because the causes are not fully understood. Additionally, controlling the heart rate does not necessarily improve symptoms.

Treatments for IST may include drug therapy, non-drug therapy, or both. Sometimes, no treatment is needed.

Drug Therapy

In some patients with IST, drug therapy can be helpful. However, achieving optimal results often requires trial-and-error attempts with several medications, singly or in combination.

Corlanor (Ivabradine)

Corlanor (ivabradine) is a heart failure drug that is prescribed off-label to treat IST. Ivabradine directly affects the "firing rate" of the sinus node, thereby reducing the heart rate.

Ivabradine is not currently approved to treat IST, but studies show it can be an effective treatment. The primary drawback of the drug, though, is that it is not safe for use during pregnancy.

Beta-Blockers

Beta-blockers are another category of drugs used to treat IST. They block the effect of adrenaline on the sinus node. Since people with IST have an exaggerated response to adrenaline, these drugs may help reduce the symptoms of IST.

Beta-blockers prescribed to treat IST and other types of tachycardia include:

  • Corgard (nadolol)
  • Inderal (propranolol)
  • Lopressor (metoprolol)
  • Sectral (acebutolol)
  • Tenormin (atenolol) 
  • Zebeta (bisoprolol) 

However, these medications can also cause low blood pressure, which may counteract their ability to relieve IST symptoms. Beta-blockers can also have unpleasant side effects, including stomach upset, dizziness, and fatigue.

Calcium Channel Blockers

Calcium channel blockers (CCB) can directly slow the action of the sinus node. They work by preventing calcium from entering the muscle cells of the heart and arteries. This helps to relax and open up narrowed blood vessels, thereby reducing heart rate.

Common calcium channel blockers used to treat tachycardia and arrhythmias include:

  • Calan SR (verapamil)
  • Cardizem (diltiazem)
  • Norvasc (amlodipine)
  • Plendil (felodipine)

However, research shows CCBs are only marginally effective in treating IST. Like beta-blockers, CCBs are associated with adverse side effects, such as hypotension, which can limit their usefulness for relieving symptoms of IST.

Other Medications

Because there is some overlap between IST and other dysautonomia syndromes (especially POTS and vasovagal syncope), drugs that are effective in treating these conditions can occasionally be helpful in treating patients with IST. These drugs may include:

  • Fludrocortisone which is a drug that causes sodium retention. Some dysautonomic syndromes, especially POTS and vasovagal syncope, have been shown to be related to decreases in blood volume, and a sodium-retaining drug can increase the blood volume toward normal, thereby reducing symptoms.
  • Orvaten (midodrine), a drug that causes an increase in vascular tone, helping to prevent low blood pressure
  • Serotonin-reuptake inhibitors, primarily used to treat depression and anxiety, but also have proven useful in treating several of the dysautonomia syndrome.

Sometimes, more than one medication is needed to treat IST symptoms.

Non-Drug Therapy

The following drug-free treatments may be used alongside medications or on their own.

Lifestyle Factors

Your healthcare provider may recommend making lifestyle changes to avoid things that may trigger episodes of tachycardia. This may include avoiding:

  • Alcohol
  • Caffeine
  • Nicotine
  • Stimulants, including prescription medications (like Adderall or Ritalin) and illegal drugs (like cocaine and methamphetamine)

Reducing stress can also go a long way in relieving uncomfortable tachycardia symptoms like heart palpitation. Deep breathing, meditation, and yoga have been shown to increase vagal tone, which helps to lower your resting heart rate and blood pressure.

Drink water or electrolyte drinks to maintain adequate fluid and salt intake. Dehydration can worsen IST symptoms.

Wearing compression socks, stockings, tights, and other pressure garments is also recommended for symptom relief. 

Exercise Training 

Another non-drug way to treat IST is exercise training. Research shows getting regular exercise helps to lower the heart rate naturally, increase exercise capacity, and improve symptoms over time.

Once your healthcare provider has ruled out dangerous arrhythmias and clears you for exercise, slowly add more activity to your daily routine. Follow your healthcare provider's guidance on the right type and amount of exercise for you.

Cognitive Behavioral Therapy (CBT)

Depression and anxiety commonly occur along with IST and can trigger symptoms. CBT is an effective form of psychological treatment that may reduce the risk of adverse cardiovascular events in people who experience anxiety as a symptom (or trigger) of their heart condition.

CBT will not cure IST, nor does it aim to. Rather, the treatment focuses on correcting a person's negative thoughts and helping them face reality, thus reducing the likelihood that anxiety will trigger or aggravate their symptoms.

Sinus Node Ablation

Because the sinus node is sometimes abnormal in IST, some patients may consider ablation therapy (a technique in which part of the cardiac electrical system is cauterized through a catheter) to modify the function of, or even destroy, the sinus node.

Sinus node ablation has so far achieved only limited success. While this procedure can eliminate IST in up to 80% of people immediately after the procedure, the IST recurs within a few months in the large majority of these individuals.

Waiting

One reasonable non-pharmacologic approach to managing IST is to do nothing. While the natural history of this disorder has not been formally documented, it seems likely that IST tends to improve over time in most people.

"Doing nothing" may not be an option in people who are severely symptomatic. However, many individuals with only mild IST can tolerate their symptoms once they are assured that they do not have a life-threatening cardiac disorder and that the problem is likely to improve on its own eventually.

Summary

Inappropriate sinus tachycardia causes uncomfortable symptoms associated with an increased heart rate. It is four times more common among those assigned female at birth and often affects younger adults. Heart palpitations, dizziness, chest pain, and fatigue that accompany IST can be debilitating. 

Researchers are not sure of the exact cause of IST, but it may be triggered by pregnancy, infection, or extreme emotional stress. IST is diagnosed using tests to rule out other possible causes of tachycardia, like anemia, hyperthyroidism, and POTS.

IST is treated with lifestyle changes, avoiding triggers, and medications like ivabradine and beta-blockers that lower your heart rate. Gradually increasing your exercise tolerance, keeping hydrated, reducing stress, and wearing compression garments may also help manage symptoms. 

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Richard N. Fogoros, MD
Richard N. Fogoros, MD, is a retired professor of medicine and board-certified in internal medicine, clinical cardiology, and clinical electrophysiology.