Supraventricular Tachycardia

Supraventricular tachycardia (SVT) is a fast, regular heartbeat — typically 150 to 220 beats a minute — caused by a short-circuit in the electrical wiring of the upper heart. Its signature is the way an episode behaves: it starts in a single beat, as if a switch has been flipped, and stops just as abruptly, sometimes after minutes and sometimes after hours.

It usually turns up in otherwise healthy hearts, often first noticed in the teens, twenties or thirties, and more commonly in women. An episode is frightening but very rarely dangerous, and for most people it can be cured outright.

Nearly all SVT falls into one of three patterns, which an electrophysiologist can usually tell apart from an ECG taken during an episode.

An episode is a sudden, forceful, regular pounding, often with a fluttering in the throat or visible neck pulsations, breathlessness and light-headedness. Many people feel an urge to pass urine when it stops.

You can often break an episode yourself with a vagal manoeuvre: bear down hard as if straining, ideally lying down and then having your legs lifted (the ‘modified Valsalva’), or splash your face with cold water. If an episode will not stop, or comes with chest pain or a faint, go to an emergency department, where an injection of adenosine resets the rhythm within seconds.

The prize is a 12-lead ECG recorded during an episode, which usually names the type. Between episodes we use a resting ECG (to look for the Wolff-Parkinson-White pattern), a Holter or event recorder, or a smartwatch trace. An echocardiogram is usually normal.

The definitive test, the electrophysiology study, is generally done as the first half of an ablation rather than on its own. This is arranged through an electrophysiology lab, with assessment and follow-up at Paragon Medical Centre on Orchard Road.

If episodes are rare and easily stopped, learning the vagal manoeuvres and avoiding triggers may be all you need. A beta-blocker or calcium channel blocker reduces how often episodes occur.

The definitive treatment is catheter ablation — a keyhole procedure through a vein in the groin that finds and cauterises the short-circuit. For AVNRT and AVRT the cure rate is above 95% with a low complication rate, and it is usually a day case. We often recommend it early for anyone with frequent episodes, a demanding or safety-critical job, or Wolff-Parkinson-White. Privately it costs roughly SGD 15,000 to SGD 30,000, with Medisave and insurance often applicable.