Supraventricular Tachycardia (SVT)

Your heart is beating normally one moment, then suddenly races at 150-250 beats per minute the next. This abrupt shift from normal to very fast and back again is the hallmark of supraventricular tachycardia. Unlike gradual heart rate increases from exercise or stress, SVT starts and stops within seconds, often without obvious triggers. While episodes can be frightening, especially the first time you experience one, SVT is rarely dangerous in people with otherwise healthy hearts.

Overview

Supraventricular tachycardia is a rapid heart rhythm originating above the heart’s lower chambers. The term “supraventricular” means above the ventricles, indicating the problem starts in the upper chambers or the electrical relay station between upper and lower chambers.

Normal heart rhythm starts in the sinus node, travels through both upper chambers, pauses briefly at a relay station called the AV node, then continues to the lower chambers. This organized sequence creates coordinated, efficient heartbeats. In SVT, an abnormal electrical circuit creates a short circuit that bypasses normal control, causing the heart to beat very rapidly.

The defining characteristic of SVT is sudden onset and termination. Your heart jumps from normal—perhaps 70 beats per minute—to 150-220 beats per minute within one or two beats. Episodes last from seconds to hours, then stop just as abruptly, returning to normal rhythm within a beat or two. This sudden on-off pattern distinguishes SVT from sinus tachycardia, which increases and decreases gradually.

Several types of SVT exist based on the specific electrical circuit involved. Atrioventricular nodal reentrant tachycardia, called AVNRT, is the most common type. It involves a circular electrical pathway within or near the AV node. Atrioventricular reentrant tachycardia, or AVRT, uses an extra electrical connection between upper and lower chambers, as seen in Wolff-Parkinson-White syndrome. Atrial tachycardia originates from a single spot in the upper chambers firing rapidly.

SVT affects people of all ages but often first appears in young adults or teenagers. Many people have their first episode in their 20s or 30s, though it can start in childhood or later in life. The condition is more common in women than men.

Episodes vary enormously in frequency. Some people have SVT once in their lifetime, never to recur. Others experience episodes weekly or even daily. The unpredictability is one of the most frustrating aspects—you never know when the next episode will strike.

Most people with SVT have structurally normal hearts. The problem is purely electrical, involving abnormal circuits or pathways rather than damaged heart muscle or blocked arteries.

Causes

SVT results from abnormal electrical circuits in the heart that create conditions for rapid, self-sustaining rhythms.

• Extra electrical pathways present from birth cause some SVTs. In Wolff-Parkinson-White syndrome, an extra connection between upper and lower chambers exists alongside the normal pathway. This creates a circuit where electrical signals can travel down one pathway and back up the other, circling continuously and causing rapid heartbeat. These extra pathways are congenital, meaning you’re born with them, though symptoms may not appear until adolescence or adulthood.
• Dual pathways in the AV node create another type of circuit. Some people are born with two distinct pathways through the AV node instead of one. These pathways conduct electrical signals at different speeds. Under certain circumstances, an electrical signal can travel down one pathway and back up the other, creating a circular pattern that sustains rapid rhythm. This is the basis of AVNRT, the most common SVT type.
• Abnormal automaticity means a spot in the upper chambers develops the ability to fire electrical signals rapidly and independently. Normally, only the sinus node generates rhythmic impulses. In atrial tachycardia, another location takes over, firing faster than the sinus node and driving the heart rate.
• Triggers that start episodes vary between individuals. Stress and anxiety commonly precipitate SVT by increasing adrenaline levels. Caffeine triggers episodes in some people, though not everyone with SVT is caffeine-sensitive. Alcohol can provoke SVT in susceptible individuals. Dehydration lowers the threshold for triggering episodes. Lack of sleep makes SVT more likely in many people.
• Physical triggers include sudden position changes, bending over, or bearing down during bowel movements. Exercise triggers SVT in some people, while others find exercise suppresses it. Deep breathing, particularly sudden deep breaths, can initiate episodes.
• Underlying conditions rarely cause SVT but can contribute. Thyroid problems, particularly hyperthyroidism, increase SVT frequency. Some lung diseases are associated with certain SVT types. Heart disease is usually not present in people with SVT, though the two can coexist.
• Medications and substances occasionally trigger SVT. Stimulant medications for ADHD or asthma can provoke episodes. Decongestants containing pseudoephedrine are common culprits. Recreational drugs, particularly stimulants like cocaine or methamphetamine, can trigger dangerous episodes.
• Pregnancy increases SVT frequency in women who already have the condition. Hormonal changes and increased blood volume contribute to this.

Sometimes no trigger is identifiable. Episodes occur randomly without apparent cause, which is frustrating but common.

Symptoms

SVT symptoms range from barely noticeable to quite distressing, depending on how fast your heart beats and how long episodes last.

• Palpitations are the universal symptom. You feel your heart suddenly racing, pounding, or fluttering in your chest. The sensation is often described as your heart “taking off” or “going crazy.” Because SVT starts so suddenly, the moment it begins is usually very noticeable.
• A fluttering or vibrating sensation in your chest, neck, or throat is common. Some people feel their pulse pounding in their neck or ears.
• Dizziness or lightheadedness occurs when your heart beats so fast that chambers don’t fill properly between beats, reducing blood flow to your brain. You might feel unsteady or like you might faint, though actual fainting from SVT is uncommon in people with normal hearts.
• Shortness of breath develops because your heart isn’t pumping efficiently at very rapid rates. You might feel like you can’t catch your breath or need to breathe deeply.
• Chest discomfort or pressure can occur during episodes. This results from your heart working very hard and needing more oxygen than it’s receiving. The discomfort usually isn’t severe and improves when the episode ends.
• Anxiety is both a trigger and a symptom. The sudden onset of rapid heartbeat is frightening, causing anxiety that releases more adrenaline, potentially prolonging the episode. This creates a difficult cycle.
• Fatigue during or after episodes is common, particularly if episodes last for hours. Your heart is working much harder than normal, which is exhausting.
• Weakness in your legs might occur, making it difficult to stand or walk during episodes.
• Nausea sometimes accompanies SVT, particularly if you’re also feeling anxious or dizzy.
• The need to urinate frequently after episodes affects some people. Rapid heart rate triggers hormone release that increases urine production.
• Some people have minimal symptoms despite very fast heart rates. They notice their heart racing but don’t feel particularly unwell. Others are highly symptomatic even with moderately elevated rates.

The sudden termination of SVT is often as noticeable as its onset. You feel your heart abruptly return to normal, sometimes accompanied by a brief pause or strong beat as normal rhythm resumes.

Diagnosis

Diagnosing SVT involves confirming rapid rhythm episodes and identifying the specific type.

• Your description of episodes is crucial. Doctors rely heavily on your account of what you experience. The sudden onset and termination are key diagnostic clues. If you can check your pulse during an episode, the rate information helps—SVT typically causes rates of 150-220 beats per minute with perfectly regular rhythm despite the rapid rate.
• Capturing the rhythm on an electrocardiogram during an episode definitively diagnoses SVT. However, episodes are often brief and unpredictable, making this challenging. If you’re experiencing an episode when you visit the emergency room or doctor’s office, an immediate electrocardiogram shows the rhythm pattern and identifies the specific SVT type.
• Extended monitoring helps capture intermittent episodes. Event monitors worn for weeks allow you to press a button when episodes occur, recording the rhythm. Some monitors automatically detect and record abnormal rhythms. Smartphone apps that record single-lead electrocardiograms during episodes are increasingly useful, though medical-grade confirmation is still needed.
• If you’ve never had an episode captured on electrocardiogram but describe classic SVT symptoms, your doctor might diagnose presumed SVT based on your history.
• Electrophysiology studies provide definitive diagnosis when the specific type of SVT needs identification before treatment, particularly before catheter ablation. Catheters inserted into your heart record electrical activity and can trigger SVT in a controlled environment, allowing precise identification of the abnormal circuit.
• Blood tests check for underlying causes. Thyroid function tests identify hyperthyroidism. Electrolyte panels ensure normal potassium and magnesium levels.
• Echocardiography evaluates your heart’s structure and function. Most people with SVT have completely normal echocardiograms, which is reassuring. This test rules out structural heart problems.
• Exercise stress testing might be performed if SVT occurs during or after physical activity. This helps determine whether exercise triggers your episodes.

Treatment

Treatment depends on episode frequency, severity, duration, and how much SVT affects your life.

• Acute treatment during episodes focuses on stopping the rapid rhythm. Vagal maneuvers are simple techniques that stimulate the vagus nerve, which can interrupt the electrical circuit causing SVT. The Valsalva maneuver—bearing down as if having a bowel movement while holding your breath for 10-15 seconds—works for many people. Carotid sinus massage, where a doctor gently presses on your neck, also stimulates the vagus nerve. Immersing your face in ice-cold water or drinking ice water quickly helps some people. These techniques work by temporarily slowing electrical conduction through the AV node, breaking the circuit.
• If vagal maneuvers don’t work, medications given intravenously can stop episodes. Adenosine is most commonly used, causing a very brief pause in AV node conduction that interrupts the circuit. The medication works within seconds but can cause temporary chest discomfort and flushing. Other medications including beta-blockers or calcium channel blockers also terminate SVT.
• For very prolonged episodes or severe symptoms, electrical cardioversion using synchronized shocks restores normal rhythm quickly. This requires sedation.
• Long-term prevention strategies depend on episode frequency and impact. If episodes are infrequent and brief, you might need no preventive treatment beyond learning vagal maneuvers to stop episodes when they occur.
• Daily medications prevent episodes in people with frequent or prolonged SVT. Beta-blockers like metoprolol reduce episode frequency and sometimes make episodes easier to terminate. Calcium channel blockers such as diltiazem or verapamil also prevent SVT. Antiarrhythmic medications including flecainide or propafenone are sometimes used for difficult-to-control SVT.
• “Pill-in-the-pocket” approach means taking medication only when episodes occur rather than daily. Some people carry medication to take at episode onset, which stops the rhythm within 30-60 minutes. This works for people with infrequent but prolonged episodes.
• Catheter ablation offers potential cure. This procedure destroys the abnormal electrical pathway or circuit causing SVT. Success rates are very high, typically 90-95% or better for most SVT types. The procedure takes a few hours, requires overnight hospital stay, and has relatively low complication rates. After successful ablation, most people never have SVT again and don’t need medications.
• Ablation is increasingly recommended earlier in treatment rather than as a last resort. Many people choose ablation after experiencing even just a few episodes, preferring definitive treatment to living with unpredictable SVT or taking daily medications.

What Happens If Left Untreated

For most people with SVT and structurally normal hearts, leaving the condition untreated isn’t dangerous but significantly impacts quality of life.

• SVT itself rarely causes serious medical problems in people with normal hearts. Brief episodes, even if frequent, don’t damage your heart or increase risk of dangerous rhythms. However, very prolonged episodes lasting many hours can occasionally weaken the heart temporarily.
• Quality of life suffers considerably with untreated SVT. The unpredictability is extremely frustrating—never knowing when your heart might suddenly start racing creates constant anxiety. This affects work, social activities, exercise, and daily life.
• Some people restrict their activities unnecessarily, avoiding exercise, caffeine, or social situations for fear of triggering episodes. This self-imposed limitation reduces quality of life more than the SVT itself would.
• Frequent emergency room visits for episodes that could be prevented with treatment create stress, inconvenience, and expense. Each episode might feel like an emergency, leading to repeated urgent care visits.
• Psychological impact can be profound. Constant worry about when the next episode will occur, fear that something is seriously wrong with your heart, and anxiety about experiencing episodes in embarrassing situations all contribute to reduced wellbeing.
• Very rarely, sustained rapid heart rates over many hours or days can lead to temporary heart muscle weakening. This is uncommon and usually reversible with rate control, but represents the main medical risk of untreated SVT.
• Some people develop panic disorder or health anxiety after experiencing SVT, sometimes having difficulty distinguishing between panic attacks and actual rhythm episodes.

What to Watch For

Most SVT episodes don’t require emergency care, particularly once you’ve been diagnosed and know what you’re experiencing. However, certain situations warrant medical attention.

• Seek emergency care if you experience SVT with severe chest pain, especially if pain is crushing, radiates to your arm or jaw, or is accompanied by sweating and nausea. While SVT doesn’t cause heart attacks, you could be having one coincidentally.
• Call emergency services if you faint or nearly faint during an episode. Brief lightheadedness is common and not concerning, but actual loss of consciousness warrants urgent evaluation.
• Head to the emergency room if an episode lasts much longer than your typical pattern. If your episodes usually last minutes but one continues for hours despite your usual techniques to stop it, seek medical care.
• Contact your doctor if you’re having your first episode ever. While likely not an emergency, new onset SVT warrants evaluation to confirm the diagnosis and discuss treatment options.
• Report to your doctor if episode frequency increases significantly. If you typically have SVT once every few months but suddenly experience daily episodes, this change needs evaluation.
• If you develop new symptoms with episodes that you haven’t experienced before—such as significant shortness of breath, chest pain, or extreme dizziness—contact your doctor.
• After successful catheter ablation, report any symptoms suggesting SVT recurrence. While uncommon, the abnormal pathway can occasionally recover or a different pathway might become active.

Potential Risks and Complications

SVT itself carries minimal risks in people with structurally normal hearts, but treatments have potential complications.

• The main risk from SVT is injury from fainting during episodes. Falling and hitting your head or fracturing bones can occur if you lose consciousness, though fainting from SVT is uncommon in people with normal hearts.
• Very prolonged episodes can rarely weaken the heart muscle temporarily. This typically requires sustained rates above 150 for many hours to days. The condition is usually reversible with treatment.
• Medication side effects vary by drug. Beta-blockers can cause fatigue, dizziness, and exercise intolerance. Calcium channel blockers might cause swelling, constipation, or dizziness. Antiarrhythmic drugs have more serious potential side effects including paradoxically causing new arrhythmias.
• Catheter ablation, while highly effective, carries risks. Bleeding or blood clots at catheter insertion sites occur occasionally. Damage to the heart’s normal electrical pathways can happen, potentially requiring pacemaker implantation in about 1% of procedures. Heart perforation is extremely rare but possible. Stroke risk is very low but exists with any heart catheterization. Overall, serious complications occur in less than 2-3% of procedures.
• Radiation exposure from fluoroscopy during ablation is a consideration, particularly for young people who might undergo the procedure. Modern techniques minimize radiation.
• Recurrence after ablation occurs in about 5-10% of people. Some need repeat procedures.
• Psychological risks include anxiety about episodes and health-related worry that can persist even after successful treatment.

Diet and Exercise

Lifestyle factors significantly influence SVT frequency and severity for many people.

• Exercise is generally beneficial and safe with SVT. Regular physical activity improves cardiovascular fitness and might reduce episode frequency. However, if exercise triggers your episodes, discuss appropriate activity levels with your doctor. After successful ablation, exercise restrictions are typically unnecessary.
• Identify your personal triggers by keeping a diary. Note what you were doing, eating, drinking, or experiencing before episodes. Patterns often emerge—perhaps caffeine triggers your SVT, or episodes occur when you’re sleep-deprived. Once you know your triggers, you can moderate them.
• Caffeine affects people differently. Some with SVT tolerate coffee and tea without problems, while others find even small amounts trigger episodes. If caffeine seems to provoke your SVT, reduce or eliminate it. Remember it’s found in coffee, tea, energy drinks, sodas, chocolate, and some medications.
• Alcohol triggers SVT in many people. Even moderate drinking can provoke episodes in susceptible individuals. If you notice a connection, limiting or avoiding alcohol helps.
• Stay well-hydrated. Dehydration lowers the threshold for SVT in many people. Adequate water intake throughout the day helps prevent episodes.
• Avoid energy drinks, which combine very high caffeine with other stimulants and commonly trigger SVT.
• Get adequate sleep. Sleep deprivation increases SVT frequency in many people. Prioritize consistent sleep schedules and good sleep hygiene.
• Manage stress through techniques that work for you—regular exercise, meditation, yoga, deep breathing, or counseling. Stress is a common SVT trigger, and reducing overall stress levels helps prevent episodes.
• Avoid recreational drugs, all of which can trigger dangerous arrhythmias.
• Some people notice digestive triggers. Large meals, certain foods, or excessive gas might provoke episodes, possibly through vagus nerve stimulation. If you notice patterns, adjusting eating habits helps.

Prevention

While you can’t prevent the underlying electrical abnormality causing SVT, you can reduce episode frequency.

• Learn and practice vagal maneuvers when you’re not having an episode. Knowing how to perform these techniques effectively helps you stop episodes quickly when they occur, reducing their impact.
• Identify and avoid your personal triggers. If caffeine, alcohol, stress, or lack of sleep provoke your SVT, addressing these factors reduces episodes.
• Manage overall cardiovascular health. Control blood pressure, maintain healthy weight, and treat any underlying conditions like thyroid problems or sleep apnea.
• Stay physically active with regular moderate exercise. This improves overall heart health and might reduce SVT frequency, though avoid vigorous exercise if it triggers your episodes.
• Get adequate sleep consistently. Most people need 7-9 hours nightly. Sleep deprivation is a common modifiable trigger.
• Limit stimulants including caffeine, nicotine, and medications with stimulant properties unless your doctor specifically recommends them.
• Develop stress management practices. Regular relaxation, meditation, or other stress-reduction techniques lower baseline stress levels and reduce SVT triggers.
• If medications prevent your episodes, take them consistently as prescribed. Skipping doses allows breakthrough episodes.
• After successful ablation, there’s no specific prevention needed since the abnormal pathway has been eliminated. However, maintaining general heart health remains important.

Key Points

• SVT is characterized by sudden onset and termination—your heart rate jumps from normal to very fast within a beat or two, then returns to normal just as abruptly. This on-off pattern is the key diagnostic clue.
• Most people with SVT have structurally normal hearts. The problem is purely electrical, involving abnormal circuits rather than damaged heart muscle. This is reassuring and means SVT rarely causes serious complications.
• Learning vagal maneuvers gives you a tool to stop episodes yourself. Many people successfully terminate most episodes at home without needing emergency care.
• Catheter ablation offers very high cure rates for SVT. Success rates typically exceed 90-95%, and most people never have SVT again after successful ablation. This makes it an attractive option for many people, even those with infrequent episodes.
• Treatment decisions are based on how much SVT affects your life rather than medical danger. If episodes are brief, rare, and easily stopped with vagal maneuvers, you might not need treatment. If episodes are frequent, prolonged, or significantly impact your quality of life, treatment options including medications or ablation are worthwhile.
• The first episode is often the scariest because you don’t know what’s happening. Once diagnosed and you understand what you’re experiencing, subsequent episodes typically cause less anxiety.
• SVT is more of a quality of life issue than a medical emergency for most people. While episodes are uncomfortable and disruptive, they’re rarely dangerous in people with normal heart structure.
• Pregnancy doesn’t preclude having SVT, though it might increase episode frequency. SVT can be safely managed during pregnancy with guidance from your cardiologist and obstetrician.
• If you’ve been diagnosed with SVT, work with a cardiologist to understand your specific type, learn techniques to stop episodes, and discuss treatment options. Whether you choose to manage episodes as they occur, take preventive medications, or undergo ablation depends on your symptoms, preferences, and lifestyle. The goal is finding the approach that allows you to live without constant worry about your heart while minimizing treatment burden.

You may also like to read these:

Arrhythmias

AV Nodal Reentrant Tachycardia (AVNRT)

Reference: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5135523/