Inappropriate Sinus Tachycardia
Inappropriate sinus tachycardia (IST) is a health problem in which the heart beats very quickly without a good reason. Read on to learn more about causes, symptoms, diagnosis, and treatment.
What is inappropriate sinus tachycardia?
Inappropriate sinus tachycardia (IST) occurs when the heart beats very quickly without a good reason. It's a type of heart rhythm abnormality called an arrhythmia.
Tachycardia is the medical term for a fast heart rate. In adults, a heart rate faster than 100 beats per minute when a person is at rest is considered tachycardia. Children and infants normally have faster heart rates than adults. Most people with IST have a resting heart rate faster than 100 beats per minute. Or they have an average resting heart rate faster than 90 beats per minute over a 24-hour period. In others, the heart rate is normal when resting, but it shoots up very quickly during light physical effort.
The heart’s electrical signal usually starts in the sinoatrial (SA) node. This collection of special cells is found in the heart’s right upper chamber. It triggers an electrical signal. The signal spreads throughout the heart and makes the heart beat. The SA node receives signals from nerves. These nerves can make the heart beat more quickly or more slowly, depending on the body’s needs.
There are many normal reasons why the heart might beat faster. These include having a fever, exercising, and feeling anxiety or stress. But IST makes the heart beat faster for unknown reasons. The heart rate may increase on its own. Other times, it rises because of a trigger. But it increases more than it should. If the heart beats too quickly, it may not be able to fill up all the way with blood between beats. Less blood may then get out to the body.
IST is rare. It's more common in young women than in men. It's also complicated. A cardiologist is the kind of specialist you'd want to see about it.
What causes IST?
IST has many causes. Experts don't understand all of them well. Sometimes, IST results from inappropriate, or wrong, signaling of the nerves that make the heart beat faster. The nerves that lower the heart’s rate may also not work as they should.
In some people, IST starts after an infection from a virus. In this case, symptoms go away suddenly after several months to a few years.
Many things can trigger just a faster heart rate. Some may include:
Caffeine.
Alcohol.
Nicotine.
Illegal drugs such as cocaine.
Overactive thyroid (hyperthyroidism).
Fever.
Anxiety.
Anemia.
Very low blood pressure.
Heart attack.
Heart failure.
Lung disease.
Pain.
A faster heart rate would be a normal response to these triggers. But usually with IST, the heart rate is high even when these triggers are not there. In some cases of IST, the heart rate may increase even more than it should because of these triggers.
What are the symptoms of IST?
While some people with IST don't have any symptoms, others do. Possible symptoms include:
Rapid heartbeat (palpitations), which may be uncomfortable.
Shortness of breath.
Dizziness.
Fainting.
Chest pain.
Anxiety.
Headaches.
Less ability to exercise.
The symptoms of IST may look like other health problems. Always see your doctor for a diagnosis.
You might be more likely to have IST symptoms if you have another heart problem. These symptoms might come on from a trigger like caffeine. They may happen from time to time over months or years. In some people, these symptoms go away after a few months.
How is IST diagnosed?
Your doctor will review your health history and do a physical exam. They can find a fast heartbeat by taking your pulse. But it's important to rule out other causes for the fast heartbeat. It's also important to know what type of tachycardia you have. Different types of tachycardia may need different treatment.
Your doctor may use tests to help make this diagnosis. These include:
Electrocardiogram. This is done to analyze the heart’s electrical rhythm. It can show the type of tachycardia you have.
Continuous monitoring of the heart rhythm (Holter monitor). This checks the rhythm for a longer period of time.
Blood tests. These are done to look for other causes of the fast heartbeat.
Echocardiogram. This checks the heart's size, structure, and ability to pump blood.
Chest X-ray. This gives a view of the heart and lungs.
IST is sometimes diagnosed by mistake as an anxiety disorder.
How is IST treated?
Several treatments are available to treat IST. Your doctor might suggest that you:
Cut out possible triggers or stimulants in your diet. These include caffeine, nicotine, and alcohol.
Take medicine to slow the heart rate. The medicines include ivabradine, beta-blockers, and calcium channel blockers.
Exercise to improve your quality of life and maintain a healthy heart.
IST is often hard to treat. If you have severe symptoms that don’t respond to these treatments, you may have a catheter ablation. This procedure uses energy to destroy a very small part of the heart that is triggering the fast heartbeat. But it doesn't always work. Also, there is some risk that destroying too much heart tissue might make a permanent pacemaker necessary.
What can I do to prevent IST?
It may not be possible to prevent IST itself. If you have IST, staying away from triggers may help you prevent episodes of increased heart rate.
Heart disease can make symptoms of IST worse. Talk with your doctor about ways you can prevent heart disease. These include:
Eating a heart-healthy diet.
Getting enough exercise and staying at a healthy weight.
Treating conditions such as unhealthy cholesterol levels, high blood pressure, and diabetes.
When should I contact my doctor?
Contact your doctor if your symptoms are becoming more frequent or severe. Call
Key points about IST
With IST, the heart beats more than 100 times per minute, even when resting. Or it beats more than 90 beats per minute when averaged over the day.
Most often, this increased heart rate happens on its own, without any triggers that make it go faster. Other times, the heart rate increases because of a trigger. But the increase is much more than what would be expected.
Some people don’t have any symptoms from IST. But others do.
Treatments vary depending on how bad your symptoms are.
It may help to stay away from possible triggers like caffeine, nicotine, and any others that cause your IST.
Next steps
Here are some tips to help you get the most from a visit to your doctor:
Know the reason for your visit and what you want to happen.
Before your visit, write down questions you want answered.
Bring someone with you to help you ask questions and remember what your doctor tells you.
At the visit, write down the name of a new diagnosis. Note any new medicines, treatments, or tests. Also write down any new instructions your doctor gives you.
Know why you're getting a new medicine or treatment and how it will help you. Also know what the side effects are.
Ask if your condition can be treated in other ways.
Know why a test or procedure is recommended and what the results could mean.
Know what to expect if you don't take the medicine or have the test or procedure.
If you have a follow-up visit, write down its date, time, and purpose.
Know how you can contact your doctor if you have questions.