The term tachycardia comes from the Greek tachys, meaning quick, and kardia (heart) – in other words: an abnormally quick heartbeat. It’s known as supraventricular tachycardia because the condition originates in the upper chambers of the heart, above (“supra”) the lower chambers or ventricles. While a normal heart rate is around 60 to 100 beats per minute (bpm), a heart with tachycardia beats at more than 100 bpm, and sometimes as fast as 150 to 240 bpm. There are several different types of SVT. These include atrioventricular nodal reentrant tachycardia or AVNRT (the most common form) and atrioventricular reciprocating tachycardia or AVRT (which may occur in a condition known as Wolff Parkinson White syndrome or WPW). Other types of SVT include atrial fibrillation, which usually causes an irregular heartbeat, and atrial tachycardia.
SVT is essentially caused by faulty electrical signals or channels in the upper chambers of the heart (the atria). A common factor is an extra electrical pathway or focus that allows a higher rate of conduction of electrical signals from the atria to the ventricles; this prompts the heart to contract more rapidly than it would normally. It’s not always easy to determine why this happens in the first place, but we do know that there are some common triggers (in almost all cases, these are triggers of the abnormal circuit rather than the cause of the abnormal electrical pathway or focus within the heart).
Potential triggers include:
- Stress or tiredness
- Drinking caffeine
- Drinking alcohol or taking drugs
- Particular types of medicine
- Extra (ectopic) heartbeats
SVT can cause a range of symptoms, including palpitations and a fluttering or racing sensation in the chest. Other symptoms include feeling lightheaded, dizzy or losing consciousness (although this is uncommon), chest pains and shortness of breath. Serious symptoms such as collapse or loss of consciousness or chest pain should be investigated straight away. SVT symptoms can last for a few minutes to several hours. They can also vary quite widely in frequency – some people experience them several times a day, others only once every few months. In some cases SVT doesn’t cause noticeable symptoms at all, so it may only be picked up during other medical investigations.
SVT can affect people of all ages, from babies to the elderly. Where younger patients are concerned, this may be because they were born with an extra electrical pathway in their hearts (an Accessory pathway or Wolff-Parkinson-White syndrome); for others, the condition simply develops later in life, in an otherwise normal heart. SVT in general tends to be more common in young women, particularly during pregnancy.
The usual way to diagnose SVT is with an electrocardiogram (ECG), a straightforward test that uses electrodes on the skin to view your heart’s electrical impulses. We might also ask you to take a Holter or Event monitor home with you – this is a portable ECG that you can wear for 24 hours or more. Another diagnostic option is an implantable loop recorder, a small device that is placed underneath the skin to track abnormal rhythms. Developments in mobile technology have also created a number of options for using a smartphone or watch to record an ECG or pulse rate that can help us to investigate symptoms of a possible SVT.
SVT is rarely life-threatening. In fact, once it has been properly investigated and diagnosed, many people are able to live with the condition without requiring immediate treatment, particularly if their symptoms are mild or happen infrequently. We may recommend certain techniques to stop occurrences of SVT when they happen. For example, the Valsalva manoeuvre uses a forceful blowing technique to alter the heart’s electrical conduction temporarily, which can then stop an SVT. Some cases of SVT do require hospital treatment, however. Some of the potential treatment options include:
Medication – medicines like beta blockers, calcium channel blockers or other anti-arrhythmic medicines to control your heart rate and slow the speed of your pulse.
Catheter ablation for SVT – a keyhole surgery procedure that uses high-frequency electrical energy or freezing (Cryoablation) to destroy the area of tissue that is causing the electrical ‘short-circuiting’ effect.
Electrical cardioversion – a procedure that applies a short electrical current to ‘re-set’ the heart and restore its normal rhythm (although this is rarely necessary in SVT).