Supraventricular Tachycardia

Types of Supraventricular Tachycardia

• Atrioventricular Nodal Reentrant Tachycardia (AVNRT):
  • The most common type of SVT.
  • Involves an extra electrical pathway within or near the AV node itself, creating a "short circuit" that causes the electrical impulse to rapidly re-enter and re-excite the atria and ventricles.
• Atrioventricular Reciprocating Tachycardia (AVRT) / Wolff-Parkinson-White (WPW) Syndrome:
  • Involves an extra, abnormal electrical pathway (accessory pathway) connecting the atria and ventricles, bypassing the AV node.
  • The electrical impulse travels down one pathway (e.g., AV node) and up the accessory pathway (or vice versa), creating a re-entry loop.
  • WPW syndrome is a specific condition where this accessory pathway causes symptoms.
• Atrial Tachycardia (AT):
  • Originates from an abnormal electrical focus (a single irritable spot) in the atria, outside of the sinus node (the heart's natural pacemaker).
  • This focus fires rapidly and sends impulses to the ventricles.
• Paroxysmal Supraventricular Tachycardia (PSVT):
  • A general term used to describe SVT episodes that start and stop suddenly (paroxysmal).
  • Often used interchangeably with AVNRT or AVRT clinically, as they are common causes of paroxysmal episodes.

Causes and Triggers

• Abnormal Electrical Pathways or Circuits:
  • As described in the types above, the presence of extra pathways (e.g., in WPW syndrome) or re-entry circuits within the AV node (AVNRT) creates the substrate for SVT.
  • Abnormal automaticity (cells firing spontaneously) can also cause atrial tachycardia.
• Triggers (Can initiate an SVT episode in susceptible individuals):
  • Stress and Anxiety: Emotional stress can activate the sympathetic nervous system.
  • Fatigue and Lack of Sleep.
  • Caffeine: Excessive intake of coffee, tea, energy drinks.
  • Alcohol: Especially binge drinking.
  • Nicotine: From smoking or vaping.
  • Certain Medications:
    • Cold and allergy medications (e.g., pseudoephedrine, phenylephrine).
    • Asthma medications (e.g., bronchodilators).
    • Thyroid medications (if dosage is too high).
    • Stimulants (e.g., for ADHD).
  • Illicit Drugs: Cocaine, amphetamines.
  • Dehydration or Electrolyte Imbalance.
  • Intense Physical Exertion.
  • Hormonal Changes: Pregnancy, menstrual cycle.
  • Underlying Heart Conditions: While often occurring in healthy hearts, SVT can sometimes be associated with heart disease, previous heart attack, or heart failure.
• No Identifiable Cause: Many SVT episodes occur spontaneously without an obvious trigger.

Symptoms

• Palpitations: A sudden sensation of a rapid, pounding, fluttering, or racing heartbeat. This is the most common symptom.
• Dizziness or Lightheadedness.
• Shortness of Breath (Dyspnea).
• Chest Discomfort or Pain.
• Anxiety.
• Fatigue.
• Fainting (Syncope) or Near-Fainting: Less common, but can occur if the heart rate is extremely fast and blood pressure drops significantly.
• Sweating.
• Nausea.
• Polyuria: Increased urination during or shortly after an episode (due to increased pressure in the atria).

Diagnosis

• Medical History and Physical Exam: The doctor will ask about symptoms, their frequency, duration, and any known triggers. Listening to the heart during an episode can reveal a very fast, regular rhythm.
• Electrocardiogram (ECG/EKG):
  • The most important diagnostic tool. It records the electrical activity of the heart.
  • An ECG taken during an SVT episode shows a rapid heart rate (typically 100-250 bpm) with narrow QRS complexes, indicating the electrical impulse originates above the ventricles.
• Holter Monitor: A portable ECG device worn for 24-48 hours (or longer) to record heart activity during daily activities. Useful for capturing infrequent SVT episodes.
• Event Monitor: A portable device worn for weeks or months that can be activated by the patient when symptoms occur, or set to automatically record abnormal rhythms.
• Implantable Loop Recorder (ILR): A small device implanted under the skin for long-term monitoring (up to 3 years) for very infrequent episodes.
• Electrophysiology (EP) Study:
  • An invasive procedure where thin, flexible catheters are threaded through veins into the heart.
  • Used to precisely map the heart's electrical pathways, locate the abnormal circuit causing SVT, and induce the SVT to confirm diagnosis. Essential for planning ablation procedures.
• Blood Tests: To rule out underlying conditions that can mimic or contribute to SVT (e.g., thyroid disease, electrolyte imbalances, anemia).

Treatment

• Acute Treatment (to stop an ongoing SVT episode):
  • Vagal Maneuvers: Simple techniques that stimulate the vagus nerve to slow heart rate. Examples:
    • Bearing down (Valsalva maneuver) as if having a bowel movement.
    • Gagging.
    • Plunging your face into ice water (diving reflex).
    • Coughing forcefully.
  • Adenosine: An intravenous medication given in a hospital setting. It temporarily blocks the AV node, often stopping the SVT. It has a very short half-life and can cause a brief, uncomfortable sensation.
  • Beta-Blockers or Calcium Channel Blockers (IV): Can also be given intravenously to slow the heart rate.
  • Cardioversion: (Rarely, for unstable patients) A controlled electrical shock to the chest to reset the heart's rhythm.
• Preventive Treatment (to reduce frequency of episodes):
  • Lifestyle Modifications: Identify and avoid individual triggers like excessive caffeine, alcohol, nicotine, or stress. Ensure adequate sleep.
  • Medications:
    • Beta-Blockers: (e.g., metoprolol, propranolol) Slow heart rate and reduce the likelihood of SVT episodes.
    • Calcium Channel Blockers: (e.g., verapamil, diltiazem) Slow heart rate and block certain pathways.
    • Antiarrhythmic Drugs: (e.g., flecainide, propafenone, amiodarone) Used for more refractory cases, but have more potential side effects.
• Catheter Ablation:
  • A highly effective, often curative procedure for many types of SVT.
  • Performed during an EP study, catheters are used to precisely locate and then destroy (ablate) the small area of heart tissue responsible for the abnormal electrical circuit, using heat (radiofrequency ablation) or cold (cryoablation).
  • Generally recommended for recurrent, symptomatic SVT that impacts quality of life, or for specific types like WPW syndrome.

Managing SVT Between Episodes

Most people with SVT have long stretches without an episode, so the practical questions matter most: what to do in the first minutes of an attack, when to go to the emergency department, and when to have the circuit ablated.

The maneuver that actually works

The modified Valsalva maneuver stops far more episodes than straining alone: bear down hard for about fifteen seconds while sitting, as if blowing into a syringe, then immediately lie flat with the legs lifted for another fifteen seconds; it can be repeated once. An episode that has not stopped after that, or one with chest pain, fainting, or breathlessness, is an emergency department visit, where adenosine ends nearly all of them in seconds. A smartwatch ECG recorded before the episode stops is the most useful thing a patient can do for the diagnosis; our wearable devices guide covers which produce a usable tracing.

Daily medication, and the pill-in-the-pocket alternative

Daily metoprolol, verapamil, or diltiazem reduces episodes without eliminating them, and fatigue or low blood pressure is common. For infrequent episodes, a single dose taken at onset can end them, set up with a cardiologist. In Wolff-Parkinson-White syndrome, digoxin and verapamil are avoided and ablation is preferred, because they can make a dangerous rhythm more likely if atrial fibrillation occurs.

When ablation is the right answer

Catheter ablation cures the large majority of cases in a single outpatient procedure, and the main risk, damage to normal conduction requiring a pacemaker, is uncommon. It is the usual recommendation for recurrent symptomatic episodes, for anyone who would rather not take a daily drug for decades, and for pilots, drivers, and athletes who cannot accommodate an attack.

Triggers in a Florida summer, and pregnancy

Dehydration, heat, alcohol on the water, energy drinks, and decongestants such as pseudoephedrine account for many local episodes; see our hydration guide. Hyperthyroidism and anemia are checked when episodes become more frequent. SVT often first appears in pregnancy, when the maneuvers and most rate-controlling drugs remain usable.

What SVT is confused with

A racing heart that builds over a minute on standing is more often POTS, an irregular racing pulse is atrial fibrillation or atrial flutter, which carry a stroke risk SVT does not, and a pounding heart with fear that peaks over minutes may be a panic attack, though the two coexist often enough that a tracing settles it. Premature beats feel like a skip, not a run. Our palpitations article sorts the patterns; our cardiovascular team coordinates monitoring and electrophysiology referral. The NHLBI and MedlinePlus publish patient guidance on supraventricular tachycardia.

If episodes are becoming more frequent, or you have never been offered ablation, schedule a visit.