Supraventricular tachycardia is a fast heartbeat episode that comes from the upper chambers of the heart and starts and stops suddenly. The “supra” in its name means above, and “ventricle” refers to the lower chamber of the heart. So the word supraventricular means “above the lower chambers”; this points to the upper half of the heart as the source of the fast beat.
In a healthy heart, each beat starts in the natural pacemaker area in the upper chambers. The signal spreads in order, and the heart beats at a steady rate. In SVT, an unwanted electrical loop forms in the upper chambers. This loop pushes the heart to high rates such as 150-220 beats per minute all of a sudden. When an episode starts, patients often describe it as “my heart suddenly started pounding like it was going to jump out of my chest.” An episode can last from a few minutes to a few hours and usually ends as suddenly as it started.
What causes SVT?
The most common cause of SVT is a small difference in the heart’s electrical system. This difference is usually present from birth, but symptoms may show up only years later. So a person can live for years without noticing it; then one day, the first episode happens.
There are three main mechanisms behind SVT. The first is the presence of an unwanted shortcut at the relay station between the upper and lower chambers. In this case, the electrical signal uses the shortcut and starts going around in a loop. The second is an extra electrical pathway in the upper chambers, present from birth. This is called Wolff Parkinson White (WPW) syndrome. The third mechanism is the presence of spots in the upper chambers that produce fast signals on their own.
Which mechanism is at play differs from person to person, but the result for the patient is similar: episodes of fast heartbeat that start and stop suddenly.
Triggers affect when episodes happen. Stress, lack of sleep, intense physical activity, caffeine, alcohol, smoking, and some medications can set off episodes. In some women, episodes can be tied to the menstrual cycle or pregnancy. Some patients have episodes without any clear trigger.
What are the symptoms?
The most typical feature of SVT is its “suddenness.” A person who feels perfectly fine notices the heart racing all of a sudden. The feeling is often described as “my heart is pounding in my chest,” “my heart is fluttering,” or “it beats steady but very fast.” Unlike the irregular beat of atrial fibrillation, in SVT the heart beats fast but in a steady rhythm.
As the fast beat goes on, other symptoms may join in: tightness in the chest, shortness of breath, lightheadedness, weakness, sweating, throbbing in the neck. Some patients feel a clear urge to urinate during an episode. In more severe episodes, dimming of vision or a near-fainting feeling can occur.
When the episode ends, patients often feel a deep relief. This relief sometimes comes with sudden tiredness, which is normal. The body has been working hard during the fast beat, and once it ends, the tiredness can last a few hours.
SVT episodes are often rare at first, sometimes coming only once in years. Over time, the frequency and length of episodes can grow. In some people, the opposite happens, and episodes fade on their own.
Is it dangerous?
SVT is not a life-threatening condition when there is no structural problem with the heart. The most important point about this disease becomes clear here: it is upsetting, frightening, and lowers the quality of life, but in most patients it does not lead to a directly fatal outcome.
But some situations call for attention. In people with a known heart condition or heart failure, long episodes can strain the heart. In people with an extra electrical pathway like WPW, if atrial fibrillation also develops in the upper chambers, the situation can become more risky. So in every patient diagnosed with SVT, it is checked whether WPW is also present.
Very long episodes (lasting hours and not stopping on their own) need medical attention. If dizziness, fainting, chest pain, or shortness of breath during an episode is severe, the emergency room should be reached.
What to do during an episode?
SVT episodes have an important advantage: they can be stopped at home with some simple moves. These are called vagal maneuvers. The vagus is a nerve that has the role of slowing the heart down; these maneuvers try to break the fast rhythm by stimulating the vagus nerve.
Splashing the face with cold water is one of the easiest methods. Filling a basin with cold water and dipping your face in for a few seconds, or washing your face firmly with cold water can help. The cold stimulus activates the vagus nerve and the heart rate may drop.
In the Valsalva maneuver, you take a deep breath and bear down with the nose and mouth closed, like straining on the toilet. Holding this for 10-15 seconds raises the pressure inside the chest and stimulates the vagus nerve. The episode may stop.
The modified Valsalva maneuver is a newer and more effective method. The patient sits halfway up and bears down for 15 seconds, then is quickly laid flat on the back with the legs raised at a 45-degree angle. The position is held for another 15 seconds. This method has a higher success rate than the classic Valsalva.
These maneuvers are not suitable for every patient. Special caution is needed in older patients and those with other heart conditions. The doctor tells you which one is right for you and shows you how to do it.
If the maneuvers do not work and the episode goes on for long, the emergency room should be reached. There, an IV medication that works in seconds usually stops the episode right away.
How is it diagnosed?
The most valuable test for diagnosing SVT is an ECG taken during an episode. An ECG, also called an EKG, is a simple, painless test that turns the heart’s electrical activity into a recording. An ECG taken during the episode both shows that it is SVT and can reveal the type.
But because episodes are short and end suddenly, by the time the patient reaches the hospital, the episode is often over. In that case, a Holter monitor is used. A Holter is a small portable device worn for 24 to 48 hours that records every heartbeat. The patient takes it home and goes about daily life. If an episode is caught, its type can be worked out.
For patients with rare episodes, recording devices worn for a week or longer are used. For very rare episodes, small devices placed under the skin that record for months may be considered.
After the diagnosis is confirmed or while planning treatment, an electrophysiology study may be offered. This procedure uses thin wires passed through a vein to study the heart’s electrical system in detail. The exact type of SVT is identified, and treatment can be done in the same session.
Treatment options
The treatment approach in SVT is shaped by how often the episodes happen, how severe they are, and the patient’s preference.
Watching and avoiding triggers can be enough on its own for patients with rare episodes. Cutting back on triggers like caffeine, alcohol, lack of sleep, and stress reduces the frequency of episodes. The patient learns vagal maneuvers and tries to stop the episode at home when one comes.
Medication is used to reduce episodes. Beta blockers are the most commonly prescribed. Beta blockers calm the heart’s electrical system and reduce both how often and how strongly episodes happen. In some patients, calcium channel blockers or stronger rhythm-controlling drugs are preferred. Medication reduces episodes but does not offer a lasting solution; once the medication is stopped, episodes usually return.
Catheter ablation is the treatment that offers a lasting solution in SVT. Ablation is a procedure in which the faulty signal pathway or spot is silenced with energy. A thin catheter is passed through a vein up to the heart. The spot causing the problem is mapped, and a short burst of energy at that point takes the area out of action.
The success rate of ablation in SVT is very high. In a single session, the problem is solved permanently in most patients, and they never have an SVT episode again. The procedure usually takes one to two hours, and the patient goes home the same day or after one night. The risks are low.
The decision for ablation is not pushed on every patient. For patients with frequent episodes, those who do not want to take medication, those who have side effects from medication, athletes, or those whose work involves safety risks (such as pilots or drivers), ablation comes to the forefront. Some patients prefer to live with rare episodes, and that is also an acceptable choice.
When to call the doctor
For someone already diagnosed with SVT, episodes that come more often, last longer, or feel stronger should be reviewed. New onset of dizziness, near-fainting, chest pain, or shortness of breath during an episode should also be taken seriously.
If an episode starts and does not end within 20-30 minutes despite vagal maneuvers, the emergency room should be reached. If fainting, severe shortness of breath, chest pain, or speech trouble occurs during an episode, an ambulance should be called without delay.
People who experience an SVT episode for the first time should also be evaluated. A fast heartbeat can have causes other than SVT, and the right diagnosis shapes the steps that follow.
Frequently Asked Questions
Are SVT and atrial fibrillation the same thing?
No. Both come from the upper chambers of the heart, but they are different conditions. In SVT, the heart beats fast but in a steady rhythm. In atrial fibrillation, the heart beats fast and unevenly. The treatment approaches are also different.
Will I faint during an episode?
Most patients do not faint. Lightheadedness and dimming of vision are more common. In patients who do faint, the situation is reviewed more closely; ablation is more often advised in this group.
Do SVT episodes put me at risk of a heart attack?
No. SVT does not cause heart attacks. The two are entirely different processes. In SVT, there is no blockage in the arteries; the problem is in the heart's electrical system.
I had occasional episodes since childhood. Why have they become more frequent now?
The basis of SVT is an electrical difference present from birth, but the frequency of episodes can change over a lifetime. Stressful periods, hormonal changes, pregnancy, weight gain, and increased caffeine or alcohol use can make episodes more frequent.
Can SVT come back after ablation?
In most patients it does not. SVT is one of the rhythm disorders where ablation offers the highest success rate (%95-98). A single session is enough for most patients. In a very small number, episodes may return over time; in that case, a second procedure can be done.
Do SVT episodes increase during pregnancy?
During pregnancy, blood volume rises and the heart works harder. So SVT episodes may become more frequent during pregnancy. Ablation before pregnancy is often offered to women who have episodes. For episodes that come up during pregnancy, vagal maneuvers are tried first; if medication is needed, drugs that are safe during pregnancy are preferred.
Can I do sports?
Most patients with SVT can do sports. But ablation is offered to those who do or want to do high-intensity competitive sports. Intense physical activity can trigger episodes, and having an episode on the field can pose a safety risk.
Is coughing during an episode helpful?
A strong cough raises the pressure inside the chest and can stop an episode in some patients. But it is not as effective as the Valsalva maneuver. It can be tried as an alternative.