You can develop supraventricular tachycardia (SVT) at any age, in fact, some people are born with the condition. Thankfully, in most cases, it isn’t life-threatening and doesn’t increase your risk of heart attack or stroke. However, depending on the severity of your symptoms, SVT can be a nuisance or even distressing. Here we’ll take a look at what happens during SVT, what you can do to reduce your symptoms and what treatments are available.
Your heart is a powerful muscle that pumps blood around your body. To do this effectively, it needs to contract in a coordinated way and that’s where your heart’s electrical system comes into play.
Your heart is made up of four chambers: two upper chambers, the right atrium and left atrium, and two lower chambers, the right ventricle and left ventricle. Electrical signals that arise in a special bundle of cells in your right atrium (your natural pacemaker) spread across your heart muscle in a specific pattern — this pattern is your heart rhythm.
A normal heart rhythm ensures that your heart muscle contracts properly to effectively pump blood to your lungs and the rest of your body. During SVT your heart rhythm becomes abnormal due to ‘short circuits’ or ‘hotspots’ in its electrical system that occur above your heart’s ventricles — the ‘supra’ in supraventricular tachycardia means ‘above’ in Latin.
These changes in your heart rhythm cause your heart to beat faster. In most healthy individuals, the heart rate at rest is between 60 to 100 beats per minute (bpm). In SVT, the heart rate at rest rises above 100 bpm and stays that way for several seconds, minutes or hours. In extreme cases, the heart rate may rise as high as 200 bpm. This rapid increase in your heart rate comes on suddenly and disappears just as quickly, often without any obvious triggers.
SVT occurs suddenly and as we’ve already mentioned, often without any trigger. However, for some people with SVT, triggers include a lack of sleep, changes in posture, drinking too much caffeine, exercise, recreational drug use (eg cocaine and methamphetamines) and emotional stress.
Symptoms often come and go over the course of a lifetime eg you may have symptoms as a child that go away in early adulthood but then return in your 40s or 50s, disappearing again before returning in your 70s or 80s.
SVT actually refers to a group of heart rhythm conditions that all affect the electrical signals of the heart above the ventricles and cause a rapid heart rate. SVT includes atrioventricular nodal re-entrant tachycardia (AVNRT), atrioventricular re-entrant tachycardia (AVRT) and atrial tachycardia (AT).
Atrioventricular nodal re-entrant tachycardia (AVNRT)
AVNRT is the most common type of SVT, making up around 50-60% of SVT cases. Although it is more often seen in young women, it can occur in both men and women of all ages. Unlike in a healthy heart where there is a single electrical pathway controlling how the heart contracts, in AVNRT the heart has two distinct electrical pathways. This abnormality creates an extra electrical circuit around a special bundle of cells that controls electrical signals in your heart called the atrioventricular node.
Atrioventricular re-entrant tachycardia (AVRT)
AVRT is the second-most common type of SVT and often occurs in people with a congenital disorder called Wolff-Parkinson-White syndrome. In AVRT an extra electrical pathway runs between the upper chambers of the heart (atria) and the lower chambers (ventricles), which allows an electrical ‘short-circuit’ to develop which can cause the heart to race.
Atrial tachycardia (AT)
In both AVNRT and AVRT there is an extra electrical pathway that causes a short circuit. This doesn’t occur in AT. Instead, there is a ‘hotspot’ of tissue in the heart that generates extra electrical signals and can cause the heart to race.
Getting a diagnosis of SVT can be challenging. This is because your doctor will need an ECG that shows the rhythm of your heart during an episode of SVT. If your episodes are infrequent and last only a few seconds or minutes, this can be difficult to capture. However, advances in heart monitoring technology mean that it is getting easier.
Wearable heart monitors
If you have symptoms of SVT, your doctor may recommend having your heart rhythm recorded using a wearable heart monitor. In the past, heart monitors could only record heart rhythms for 24-48 hours. However, today, newer devices such as the Zio® XT patch offer heart monitoring for up to two weeks using wire-free patches. The ability to monitor the heart for longer periods makes it more likely that an episode of SVT will be captured.
There are also smart watches that can record ECGs, which you can activate when you experience symptoms. Similarly a mobile phone attachment called AliveCor also allows you to record ECGs; when you experience symptoms, you simply place your finger on a special pad attached to your mobile phone to take a recording of your heart rhythm.
Invasive heart monitoring
For longer-term heart monitoring, you can have a loop recorder implanted just under your skin on the left side of your chest. This can monitor your heart rhythm for up to three years.
Although an episode of SVT can feel distressing, it is important to remember that you aren’t in any danger as SVT is not life-threatening. If you don’t feel any different during your episode and it goes away on its own, you can simply wait it out. However, if you feel unwell, seek medical attention.
During an episode of SVT, you can also try a variety of techniques to stop your episode. These include drinking or gulping cold water, splashing cold water on your face or closing your eyes and gently applying pressure on each eye for about five seconds.
You can also try the Valsalva manoeuvre. To do this, pinch your nose closed, close your mouth, bear down as you would when passing stools and then try to exhale. Do this for 10-15 seconds.
If you are aged under 30, you can also try carotid sinus massage. This involves using two fingers to press against the front side of your neck just under your chin and massaging this area with a circular movement.
If you only experience infrequent episodes of SVT, such as once every few years, there usually isn’t any need for treatment. However, if your symptoms are more frequent and causing you distress, your doctor may prescribe medication to reduce your symptoms.
Medications for SVT
There is a range of medication available and you may need to try more than one to find one that is most effective for you. Newer medications are in development and in the near future it may be possible to end an episode of SVT by taking a medication applied through your nose — clinical trials are currently underway.
If medication proves unsuccessful or if you prefer to avoid drugs, your doctor may recommend an electrophysiology study followed by catheter ablation. This is a minimally invasive procedure performed under local anaesthetic and sedation, which usually takes around two hours.
Several thin tubes (catheters) and wire electrodes will be passed into a vein in your groin and guided up into your heart to measure your heart’s electrical activity. In a safe and controlled way, the abnormal rhythm that causes your SVT will be triggered — this is done by pacing the heart with the catheters and sometimes certain medications are given through a vein.
This electrophysiology study, often combined with 3D mapping systems, will help identify exactly where in your heart the SVT is arising from. In the past, mapping used higher levels of X-ray radiation but advances in technology mean far lower levels are now needed.
With the tissue causing your SVT pinpointed, it will then be burned away using catheter ablation ie applying heat energy. This procedure is highly successful in most patients — over 95% of patients that undergo catheter ablation for SVT are cured.
Dr Riyaz Somani is a Consultant Cardiologist and Electrophysiologist at Spire Leicester Hospital, Spire Nottingham Hospital and Glenfield NHS Hospital, Leicester. He specialises in palpitations, flutters, atrial fibrillation, supraventricular tachycardia (SVT), dizziness, blackouts and inherited heart conditions. He also holds a PhD from the University of Leeds in the field of cardiology and performs over 200 procedures every year, including ablation for atrial fibrillation and ventricular tachycardia using 3D mapping systems as well as implantation of pacemakers and defibrillators. View Dr Somani's website.