What is a supraventricular tachycardia (SVT)?
Tachycardia means a fast heart rate. Supraventricular means 'coming from above the ventricle'.
During an episode of SVT, the heartbeat is not controlled by the SA node (the normal timer of the heart). Another part of the heart overrides this timer with faster impulses. The source or 'trigger' of the impulse in an SVT is somewhere above ('supra') the ventricles, but the impulse then spreads to the ventricles. The heart then contacts (beats) faster than normal. For example:
- A 'short circuit' in the electrical pathways of the heart may develop. The most common cause of SVT is an abnormal extra pathway from the AV node through to the ventricles. This can make electrical impulses go round and round this section of the heart.
- A small area in one of the atria may become more 'excitable' than usual and start to produce electrical impulses.
An episode of SVT usually starts suddenly for no apparent reason. It may last just a few minutes, but can last several hours. It then stops just as suddenly as it started. Rarely, an episode lasts longer than a few hours.
The time between episodes of SVT can vary greatly. In some cases, short bursts of SVT occur several times a day. At the other extreme, an episode of SVT may occur just once or twice a year. In most cases it is somewhere in between, and an episode ('paroxysm') of SVT occurs now and again.
Note: the term SVT is usually only used when the heart rate is fast and regular. Another condition which causes a fast but irregular heart rate, and is caused by abnormal impulses in the the atria, is called atrial fibrillation. This is not dealt with further in this leaflet. Another leaflet deals with atrial fibrillation.
Who gets supraventricular tachycardia (SVT)?
In most cases, the first episode of SVT begins in childhood or early adulthood. However, a first episode of SVT can occur at any age. It is an uncommon condition, but the exact number of people affected is not known.
Average rating:
ANN ROBERTS, over 2 years
I HAVE FOUND THIS SITE TO BE OF GREAT VALUE TO ME. I WAS FIRST DIAGNOSDED WITH SVT FOUR YEARS AGO. i WASN'T SURE WHAT IT REALLY WAS UN TIL I CAME ACROSS YOUR WEB SIGHT. THANK YOU REGARDS A ROBERTS
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