Supraventricular Tachycardia (SVT) is a condition characterized by a rapid, abnormal heart rhythm originating in the heart’s upper chambers. This electrical malfunction causes the heart rate to suddenly accelerate, often to over 150 beats per minute, leading to symptoms like heart palpitations, light-headedness, and shortness of breath. Treatment is necessary to break the abnormal rhythm and return the heart to its normal electrical pattern. Management goals are to acutely terminate an active episode and prevent future occurrences through long-term strategies.
Immediate Non-Medical Interventions
The first step for a person experiencing an SVT episode is often to attempt a vagal maneuver. Stimulating the vagus nerve releases a chemical that can slow the electrical conduction through the heart’s atrioventricular node, potentially breaking the rapid circuit and restoring a normal rhythm. The most common and widely recommended technique is the Valsalva maneuver, which involves bearing down as if having a bowel movement for about 15 seconds while lying down. A modified version, where the patient blows forcefully into a syringe and then has their legs raised immediately afterward, has demonstrated a success rate of approximately 43% in converting SVT to a normal rhythm.
Other physical methods that stimulate the vagus nerve include immersing the face in ice-cold water (triggering the diving reflex) or stimulating the gag reflex. A technique called carotid sinus massage involves applying gentle pressure to the carotid artery in the neck, but this should only be performed by a medical professional. The maneuver carries a small risk of dislodging plaque in patients with underlying artery disease, which could lead to a stroke. These non-invasive actions are the initial treatment for stable patients because they are quick, free of side effects, and can be performed immediately upon symptom onset.
Medication-Based Management
When immediate non-medical interventions fail, or for more severe episodes, medication becomes the next line of treatment. Acute termination of an active SVT episode in a hospital setting typically begins with an intravenous injection of Adenosine. Adenosine is a very short-acting drug, with a half-life of only about 10 seconds, which rapidly blocks electrical conduction through the atrioventricular node. This temporary electrical block effectively resets the heart’s rhythm, and the drug’s rapid clearance minimizes side effects, though it can cause a brief sensation of flushing or chest pressure.
If Adenosine is ineffective or contraindicated, other intravenous medications may be used, such as Calcium Channel Blockers (like diltiazem or verapamil) or Beta-blockers (like metoprolol). These drugs work differently than Adenosine by slowing the electrical signals through the heart’s conduction system over a longer period. For patients with frequent but non-emergency episodes, a “pill-in-the-pocket” strategy may be employed, where a patient takes an oral dose of a medication at the onset of an SVT episode.
Oral medications are prescribed for chronic management. Beta-blockers and non-dihydropyridine Calcium Channel Blockers are commonly used to reduce the frequency and severity of episodes by slowing the heart rate and modifying electrical conduction. In cases where these first-line agents do not provide sufficient control, a physician may prescribe stronger antiarrhythmic drugs. These include medications like Flecainide or Propafenone, which alter the electrical activity of the heart muscle cells, but they are generally reserved for patients who do not have underlying structural heart disease.
Definitive and Emergency Procedures
For individuals with recurrent or symptomatic SVT not adequately controlled by medication, Catheter Ablation is a treatment option. This procedure is widely considered a curative option for many types of SVT, offering a high success rate. During the procedure, thin, flexible wires called catheters are threaded through blood vessels, usually from the groin, up to the heart.
Specialized mapping techniques are used to precisely locate the small area of heart tissue responsible for the abnormal electrical circuit that causes the SVT. Once the source is identified, the catheter delivers a burst of energy—most commonly radiofrequency energy (heat) or sometimes cryoablation (freezing)—to destroy the errant electrical pathway. This targeted destruction creates a scar that permanently blocks the abnormal electrical signals, preventing future SVT episodes.
In contrast to ablation, Electrical Cardioversion is an emergency procedure reserved for patients who are hemodynamically unstable. This involves delivering a controlled, synchronized electrical shock through paddles or patches placed on the chest while the patient is sedated. The electrical current momentarily depolarizes nearly all the heart’s muscle cells simultaneously, stopping the rapid, abnormal rhythm. This allows the heart’s natural pacemaker to reset and resume a normal, organized rhythm.