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Inappropriate sinus tachycardia (IST) is a health problem in which the heart beats very quickly without a good reason. It is a type of heart rhythm abnormality called an arrhythmia.
Tachycardia is the medical term for a fast heart rate. In adults, a heart rate greater than 100 beats per minute when resting is considered tachycardia. Children and infants normally have faster heart rates. Some people with IST have a high resting heart rate. 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 node, which is found in the heart’s right upper chamber. This area triggers the electrical signal that spreads throughout the heart and coordinates the heartbeat. The sinoatrial node receives signals from nerves. These nerves can cause the heart to beat more quickly or more slowly, depending on the body’s needs.
There are many normal reasons why the heart might beat faster such as during a fever or exercise, or when you are anxious. But in IST, the heart beats faster for unknown reasons. The heart rate may increase on its own without any stimulation. Other times, the heart rate rises because of a trigger. But it increases more than it should. If the heart beats very quickly, it may not be able to fill fully between beats. Slightly less blood may then get out to the body.
IST is rare. It is more common in young women than in men. IST is a complex disorder. It is generally best to see a cardiologist trained in the use of various cardiac medicines and electrophysiologic treatments.
IST has many causes. Experts do not understand all of them well. IST sometimes results from inappropriate signaling of the nerves that increase the heart’s rate. 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. These people may have their symptoms go away suddenly after several months to a few years.
Many factors can trigger tachycardia itself. In cases of IST, the heart rate may increase more than it should in response to these triggers. Some of these things include:
Some people with IST do not have any symptoms. But others do. Possible symptoms include:
The symptoms of IST may look like other health problems. Always see your healthcare provider for a diagnosis.
You might be more likely to have symptoms from IST if you have another kind of heart problem. These symptoms might come on in response to a trigger such as caffeine. These symptoms may happen from time to time over months or years. In some people, these symptoms go away after several months.
Your healthcare provider will review your health history and do a physical exam. He or she can easily notice a fast heartbeat by taking your pulse. But, it is important to rule out other causes for the fast heartbeat. It is also important to learn what type of tachycardia is present. Other types of tachycardia may need different treatment.
Your healthcare provider might use tests to help make this diagnosis. These include:
IST is sometimes diagnosed in error as an anxiety disorder.
IST is often hard to treat. If you have severe symptoms that don’t respond to these treatments, you may need catheter ablation. This procedure uses energy to destroy a very small part of the heart that is triggering the tachycardia. But it doesn’t always work because the whole heart can be abnormal. There is also a small risk that destroying too much heart tissue might make a permanent pacemaker necessary.
It may not be possible to prevent IST itself. If you have IST, staying away from triggers may help you avoid episodes of increased heart rate. Possible triggers include:
Heart disease can make symptoms of IST worse. Talk with your healthcare provider about ways you can prevent heart disease. These include:
Call your healthcare provider if your symptoms are becoming more frequent or severe. Call 911 if you have symptoms like severe shortness of breath or chest pain.
Tips to help you get the most from a visit to your healthcare provider:
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