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Supraventricular tachycardia (SVT)

Created by Bianca Yoo.

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Video transcript

- [Voiceover] Supraventricular Tachycardia also known as SVT refers to an abnormally high heart rate. The prefix supra means above. So supraventricular means above the ventricles. This right here is the heart and right now in green I'm outlining the ventricles. So again supraventricular means above the ventricles. The term supraventricular, implies that the abnormal heart beat is starting from, at or above, the AV node which is that orange structure I circled right here. The AV node is the key player and the heart's electrical conduction system. Now tachycardia, refers to a heart rate greater than 100 beats per minute. At rest a person's heart rate should be under a 100 beats per minute. Typically, young healthy people have a heart rate between 1,580 beats per minute. Now the 100 beats per minute cutoff applies to somebody who is at rest. It can be totally normal for someone's heart rate to go above a 100 depending on the circumstance. Let's say you're the average person and you sprint 200 meters. Your muscles are moving and they're requiring more oxygen. Therefore your heart is going to increase its rate in order to supply the rest of your body and those muscles with more oxygen. So it would not be unrealistic for your heart rate to go above 100 in this case. It's even normal for a strong emotional response, like intense fear, to push your heart rate over 100. Imagine being terribly afraid of heights and cresting the world's highest roller coaster. You can imagine that at the top of that crest your heart would be beating pretty fast. That's because in times of intense fear, the body sends out chemical signals to increase your heart rate. This is another scenario where, it wouldn't be unreasonable for your heart rate to go above a 100. However, in Supraventricular Tachycardia someone's going to have a heart rate greater than a 100 beats per minute, at rest. They're not going to have just run and not in the setting of an intense emotional reaction. Now what are the signs and symptoms of an SVT? Well some people might have an SVT and not even know it. It might be what's called asymptomatic, meaning they're not showing any symptoms. People that do have symptoms might complain of, the feeling of a heart beating out of their chest. This is known as palpitations, and again, this is the feeling that their heart's beating out of their chest. They can feel it pounding. Because the heart's beating so fast and working overtime, people might also experience chest pain. So chest pain is a common complaint. When your heart beats fast some people feel anxiety. So anxiety is another symptom of SVT. Other people say that they feel short of breath. Sometimes people say they feel dizzy or that they're going to pass out. Now why do people feel dizzy? Well let's remember, the heart serves as a pump, to pump blood from the heart to the rest of the body. When the heart's at rest it fills with blood and when you feel your heart beat that's when the heart is pumping blood from the heart to the rest of the body, to supply oxygen to the tissues. If your heart's beating really fast it doesn't get the chance to fill with as much blood. Therefore, the circulation of the blood to the rest of the body, including the head, can be compromised. That's why sometimes people feel dizzy. Rarely people might even pass out but with SVTs this is a pretty rare occurrence. However, it's not uncommon for people to feel dizzy. Now how is SVT diagnosed? Well, symptoms alone aren't enough to diagnose an SVT. However they can give a practitioner clues that someone might be experiencing an SVT. If a healthcare provider suspects an SVT, they're going to order an EKG. An EKG is a device that records and reports information on the heart's electrical activity. It's also needed to diagnose an SVT and can tell you what type of SVT a person is experiencing. Now it's important to note that SVTs and other abnormal heart rhythms can be here one second and gone the next. That means a person might be experiencing symptoms of an SVT when they're at home but by the time they get to the doctor's office, their heart might have switched out of the SVT. In this case, their EKG may be normal. If a patient has a normal EKG but has been reporting symptoms of an EKG such as I've been feeling palpitations, with shortness of breath and dizzy and the healthcare provider has a strong suspicion of an SVT they can send the patient home, with a portable EKG. Now will monitor their heart's rate and rhythm over the next couple of days. If that monitor detects any strange heart rate and rhythm, it's going to alert the clinician and will record the EKG. Because there are several types of SVTs there are multiple SVT risk factors. People can have inherited genetic mutations that affect the heart cells, all the way down to the cellular level. Also, structural abnormalities that occur over a lifetime of wear and tear can increase someone's risk factor for an SVT. Another risk factor is coronary artery disease. The coronary arteries are blood vessels that supply the heart with oxygenated blood. Over years the inside of the coronary arteries can get clogged and this inhibits the flow of blood to the heart. Years of coronary artery disease leads to, chronic heart failure which is a condition where the heart has a diminished pump function and can't pump blood from the heart to the rest of the body as well. There are also risk factors outside of the heart such as, the lungs. People with COPD or chronic obstructive pulmonary disease have a higher risk of an SVT. COPD is typically found in people who have a longstanding smoking history. Also a blood clot in the lung, known as a pulmonary embolus will increase your risk of an SVT. Other non-cardiac risk factors are: years of alcohol abuse; hyperthyroidism which is a condition where the thyroid gland makes too much thyroid hormone; and pathologically high levels of certain medications such as theophylline and digitalis.