Medically reviewed by Dr Nabila Laskar, Consultant Cardiologist (GMC 7040901). Supraventricular tachycardia (SVT) is a group of arrhythmias characterised by episodes of sudden, rapid heartbeat originating above the ventricles. It is one of the most common sustained arrhythmias seen in otherwise healthy people and, while frightening during an episode, is rarely dangerous.
SVT typically presents as a sudden onset of rapid heartbeat, often described as a "racing" or "fluttering" sensation in the chest, with heart rates commonly reaching 150 to 250 beats per minute. Episodes may last seconds, minutes, or occasionally hours. Associated symptoms can include breathlessness, dizziness, chest tightness, and a pulsating sensation in the neck. The abrupt onset and offset of episodes is a characteristic feature that distinguishes SVT from sinus tachycardia, which builds and fades more gradually. Episodes can occur at rest, during exertion, or be triggered by caffeine, alcohol, or fatigue.
The most common type is AVNRT (atrioventricular nodal re-entrant tachycardia), where an abnormal electrical loop within or near the AV node causes the arrhythmia. AVRT (atrioventricular re-entrant tachycardia) involves an accessory pathway connecting the atria and ventricles, of which Wolff-Parkinson-White (WPW) syndrome is the best-known example. Atrial tachycardia arises from a single focus in the atrial tissue firing rapidly. All of these are distinct from atrial fibrillation, which has a different mechanism and different implications.
An ECG captured during an episode is the definitive diagnostic tool and will typically show a narrow-complex regular tachycardia at high rate. Because episodes are intermittent, a standard 12-lead ECG recorded between attacks is usually normal. A Holter monitor worn for 24 hours to 7 days significantly improves the chances of capturing an episode. Between attacks, the resting ECG should be examined carefully for a delta wave, the hallmark of an accessory pathway in WPW, which carries specific management implications.
Acute episodes can often be terminated by vagal manoeuvres such as the Valsalva manoeuvre or cold water immersion of the face. Medications including adenosine or verapamil are used in hospital settings to terminate acute episodes. Long-term management options include rate-controlling medication taken regularly, or catheter ablation, a minimally invasive procedure that targets and eliminates the abnormal electrical pathway responsible for the SVT. Ablation is curative in a high proportion of cases and is the treatment of choice for those with frequent or distressing episodes.
In the vast majority of cases, SVT in an otherwise healthy heart is not dangerous. The exception is WPW syndrome with certain accessory pathway characteristics, which requires specialist evaluation and carries different risk implications.
Vagal manoeuvres can terminate many SVT episodes. The modified Valsalva manoeuvre (straining as if opening bowels, then lying flat with legs raised) is the most effective technique. Your cardiologist will demonstrate this at your appointment.
A resting ECG between episodes is usually normal. Capturing an episode requires an ECG during symptoms, which is why a 7-day Holter monitor is often the most effective diagnostic approach for intermittent SVT.
Yes. Catheter ablation is a minimally invasive procedure that eliminates the abnormal electrical pathway causing SVT and is curative in a high proportion of patients. It is the treatment of choice for frequent or distressing episodes.