Paroxysmal Supraventricular Tachycardia (PSVT) involves episodes of an unusually rapid heart rate that begins and ends without warning. The term “paroxysmal” indicates the sudden, intermittent nature of these episodes, which can last from seconds to hours. PSVT is classified as “supraventricular” because the fast rhythm originates in the heart’s upper chambers, above the ventricles. While generally not life-threatening, understanding its cause and management is important.
How PSVT Disrupts the Heart’s Rhythm
The heart’s normal rhythm is governed by the sinoatrial (SA) node, the natural pacemaker in the upper right chamber (atrium). The impulse travels through the atria to the atrioventricular (AV) node, which acts as an electrical gateway between the upper and lower chambers. PSVT occurs when a structural abnormality creates a short circuit, overriding this normal rhythm.
The underlying mechanism is typically a re-entry circuit, where an electrical impulse gets caught in a loop and cycles rapidly. The two most common types are Atrioventricular Nodal Re-entrant Tachycardia (AVNRT) and Atrioventricular Re-entrant Tachycardia (AVRT). AVNRT involves dual pathways existing within or near the AV node, allowing the signal to travel in a circle.
AVRT involves an extra muscle fiber, known as an accessory pathway, that directly connects the atria and ventricles, bypassing the AV node entirely. In both AVNRT and AVRT, the signal cycles repeatedly, causing the heart to contract much faster than normal, often reaching 150 to 250 beats per minute. This rapid cycling causes the abrupt onset of tachycardia.
Recognizing the Symptoms of an Episode
The hallmark of a PSVT episode is a rapid, regular, and pounding heartbeat, known as palpitations. This racing sensation can be intense, often exceeding 100 beats per minute, and is sometimes described as a fluttering or “flip-flopping” in the chest.
The fast rate impairs the heart’s ability to fill properly, reducing blood flow to the body. This reduced flow can manifest as lightheadedness, dizziness, weakness, or fatigue. Patients may also experience shortness of breath, anxiety, or chest discomfort. Episodes are defined by their abrupt starting and stopping.
Confirming the Diagnosis
Diagnosis begins with a thorough medical history, focusing on the sudden nature and duration of the episodes. The primary tool is the Electrocardiogram (ECG), which records the heart’s electrical activity. An ECG performed during an episode shows the characteristic rapid, narrow-complex heart rhythm.
Since PSVT is paroxysmal, a routine in-office ECG often appears normal between episodes. Doctors use ambulatory monitoring devices to capture the intermittent disturbance. A Holter monitor is worn continuously for 24 to 48 hours to record all heartbeats. For less frequent episodes, an event monitor records the rhythm only when the patient activates it during symptoms. For a definitive diagnosis and to pinpoint the short circuit location, an Electrophysiology (EP) study may be performed, involving threading specialized catheters into the heart to map the electrical pathways.
Treatment and Management Strategies
Immediate intervention for a stable patient begins with simple, physical techniques known as vagal maneuvers. These maneuvers stimulate the vagus nerve, which helps slow conduction through the AV node, potentially interrupting the re-entry circuit and restoring a normal rhythm. Examples include bearing down (Valsalva maneuver) or immersing the face in cold water. The modified Valsalva maneuver, involving blowing into a syringe followed by immediately raising the legs, has shown a success rate around 43%.
If vagal maneuvers are unsuccessful, emergency treatment involves the intravenous administration of Adenosine. Adenosine is an ultra-short-acting drug that temporarily blocks conduction through the AV node, effectively stopping the re-entry circuit. Due to its short half-life of 10 to 20 seconds, its effects are brief, though patients may experience temporary flushing or chest discomfort. Other intravenous medications, including calcium channel blockers (like verapamil or diltiazem) or beta-blockers, may be used if Adenosine is ineffective.
For preventing future episodes, long-term management involves medication or a curative procedure. Oral medications, such as beta-blockers and calcium channel blockers, reduce the frequency and severity of episodes by slowing the heart rate or blocking aberrant electrical signals. This approach is chosen for individuals with infrequent or mild symptoms.
For patients with frequent, poorly tolerated episodes, catheter ablation is often the preferred and most effective treatment. This minimally invasive procedure involves guiding a catheter to the specific area of heart tissue creating the short circuit, identified during the EP study. Radiofrequency energy (heat) or cryoenergy (cold) is delivered to destroy this problematic tissue spot. Catheter ablation has a high success rate, often exceeding 90% for PSVT, offering a long-term solution by permanently eliminating the re-entry pathway.