Supraventricular tachycardia (SVT)
Overview
When to see a cardiologist
Symptoms
Causes
Complications
Overview of SVT
Supraventricular tachycardias (SVTs) are a family of common heart rhythm abnormalities that can cause a racing heart beat (palpitations). Sometimes the racing is accompanied by dizziness, chest tightness and can even lead to collapse.
Most SVTs are not harmful but a small proportion can be dangerous, or associated with other more harmful heart rhythm disturbances.
SVT can occur even in otherwise normal hearts, but rarely they can be associated with other cardiac conditions including cardiomyopathy and valve disease.
Most SVTs can be cured with an ablation procedure. The decision on whether to undertaken an ablation procedure or to manage with medications, may come down to personal choice. Occasionally patients are advised strongly to have an ablation procedure if an SVT is thought to be dangerous.
When to See a Cardiologist
SVT symptoms can be intrusive and upsetting. They can also feel very similar to other, more serious, conditions.
A cardiologist can help you confirm the diagnosis and rule out other more serious conditions as the cause of palpitation symptoms. Cardiologists generally have access to a wide range of tests and up-to-date wearable technologies for quicker and more accurate diagnosis.
Once SVT is confirmed, a cardiologist can discuss the range of treatment options, including medications and ablation procedures. You can read more about SVT ablation here.
Symptoms of SVT
A typical attack of SVT is felt as a sudden onset of racing in the chest, maybe accompanied by chest tightness or breathlessness. This generally lasts minutes, or at the most a few hours. Sometimes the start or end of an SVT attack can be accompanied by a drop in blood pressure leading to dizziness or even collapse.
Common triggers for SVT include bending over and after eating large meals. Some people with SVT can control or halt their symptoms by holding their breath in a technique called the Valsalva manoeuvre. Symptoms that stop or start in this way are more likely to be SVT than other heart rhythm abnormalities, but this is not conclusive evidence.
Causes of SVT
SVTs are caused by extra electrical connections in the heart.
Some people are born with extra electrical connections called “accessory pathways”. If these inborn extra connections lead to SVT then this is sometimes referred to as “Wolff Parkinson White syndrome”. Rarely, Wolff Parkinson White can run in families and be associated with other cardiac abnormalities.
More commonly, rather than be born with an extra connection, people develop them as they get older. This happens as some of the electrical pathways near the middle of the heart become stretched as part of the normal ageing process, leading to a form of SVT called “atrioventricular nodal re-entry tachycardia” or “AVNRT”.
AVNRT typically happens in adolescence or in early middle age (40-60yrs), and more often in women than in men, though there are many exceptions to this.
Treatments for SVT
Treatment options for SVT depend on the precise kind of SVT and the likelihood of more dangerous rhythms occurring.
Patients with intrusive symptoms can choose to take a daily medication to reduce the number of attacks. If this is not an acceptable option, or if it proves ineffective, then an EP study and ablation procedure may be recommended.
EP study (“electrophysiological study”) is a procedure performed under local anaesthetic where wires are fed to the heart and used to distinguish which sort of SVT is occurring. Once the diagnosis is confirmed then in the majority of cases, the extra electrical connections responsible can usually be burned off the surface of the heart using radiofrequency energy. The decision to undergo EP study and ablation should be taken by the patient with advice from a specialist in heart rhythm medicine (a cardiac electrophysiologist). You can read more about EP studies here.