Paroxysmal supraventricular tachycardia (PSVT) is an abnormal heart rhythm characterized by a heart rate that suddenly accelerates and then abruptly returns to normal. The term “paroxysmal” refers to this sudden, episodic nature of the racing heart rhythm, which typically originates in the upper chambers (atria) or within the atrioventricular (AV) node. While tachycardia can be alarming, PSVT is generally manageable and often not associated with underlying structural heart disease. Episodes result in heart rates ranging from 120 to 230 beats per minute or higher, far exceeding the normal resting range.
Understanding the Heart’s Electrical Circuit
The heart’s normal rhythm is governed by a precise electrical sequence, starting with the sinoatrial (SA) node, often called the heart’s natural pacemaker, in the right atrium. This impulse travels across the atria, causing them to contract, and then converges at the atrioventricular (AV) node. The AV node briefly delays the signal to ensure the ventricles fill completely before the impulse passes through to the lower chambers.
PSVT occurs when this orderly sequence is disrupted by a “short circuit.” This mechanism is known as re-entry, where the electrical impulse travels in a continuous loop instead of following the normal one-way path. The most common form is Atrioventricular Nodal Re-entrant Tachycardia (AVNRT), which involves an abnormal functional circuit within or near the AV node itself.
Atrioventricular Nodal Re-entrant Tachycardia (AVNRT)
In AVNRT, two distinct pathways exist within the AV node: a fast pathway and a slow pathway. When a premature beat occurs, the impulse may find the fast pathway temporarily refractory, or non-responsive, forcing it down the slow pathway. By the time the impulse emerges from the slow pathway, the fast pathway has recovered, allowing the signal to conduct in the reverse direction and establish the rapid electrical loop.
Atrioventricular Re-entrant Tachycardia (AVRT)
Another common type of PSVT is Atrioventricular Re-entrant Tachycardia (AVRT). This involves an additional, abnormal muscle connection, known as an accessory pathway, that links the atria and ventricles, bypassing the AV node. These accessory pathways are considered congenital anomalies, meaning they are present from birth. This allows the electrical impulse to travel rapidly down the normal route and then back up the extra pathway, creating a larger re-entry loop.
Recognizing the Signs of PSVT
The onset of a PSVT episode is marked by a sudden sensation of the heart racing, known as palpitations, that can reach rates of 140 to 280 beats per minute. Patients often describe this as a pounding, fluttering, or flip-flopping feeling in the chest or neck. The episodes are characterized by their abrupt start and equally abrupt cessation, sometimes resolving spontaneously after a few seconds or minutes.
Because the heart beats too quickly to fill properly, the body may experience reduced blood flow, leading to secondary symptoms. Common signs include dizziness, shortness of breath, anxiety, or chest discomfort.
In more severe or sustained episodes, the drop in blood pressure can lead to fainting, or syncope. Patients should seek immediate medical attention if an episode is accompanied by chest pain or if the tachycardia does not stop on its own quickly. The distressing nature of the sudden onset often causes individuals to mistake the episode for a panic attack.
Confirming the Diagnosis
Diagnosing PSVT is challenging because of its paroxysmal nature, meaning a patient’s heart rhythm may appear completely normal during a routine office visit. The primary diagnostic tool is the 12-lead Electrocardiogram (ECG), but it must be captured during an episode of the rapid heart rhythm to confirm the diagnosis. The ECG tracing allows medical professionals to analyze the heart’s electrical activity and distinguish PSVT from other types of tachycardia.
To capture infrequent events, ambulatory monitoring devices are necessary. A Holter monitor is a portable ECG device worn continuously for one to seven days. For less frequent episodes, an event monitor can be worn for a month or more, recording data only when the patient activates it during a symptomatic event or when the device detects an abnormal rhythm.
The definitive method for identifying the precise electrical mechanism and location of the short circuit is the Electrophysiology (EP) Study. This procedure involves threading specialized catheters through a vein up to the heart. These catheters are used to map the heart’s electrical pathways and safely induce the PSVT in a controlled setting, allowing doctors to pinpoint the exact location of the aberrant pathway.
Options for Treatment and Long-Term Management
Treatment involves immediate interventions to stop an acute episode and long-term strategies to prevent recurrence. The first line of defense for immediate termination involves vagal maneuvers. These simple physical actions, such as performing the Valsalva maneuver or splashing ice water on the face, stimulate the vagus nerve. This stimulation slows conduction through the AV node and can interrupt the re-entry circuit.
If vagal maneuvers fail, intravenous medications are used to abort the tachycardia. Adenosine is the most common medication, known for its extremely short half-life, as it temporarily blocks electrical conduction through the AV node, terminating the re-entry circuit. Other pharmacological options include calcium channel blockers (like verapamil or diltiazem) or beta-blockers, which also work to slow AV nodal conduction.
For long-term management, patients may be prescribed daily anti-arrhythmic medications to reduce the frequency and severity of episodes. Lifestyle modifications are also encouraged, including avoiding common triggers like excessive caffeine, alcohol, and stimulant medications. These conservative measures are often sufficient for individuals with infrequent or well-tolerated episodes.
For patients with frequent, highly symptomatic, or drug-refractory PSVT, Catheter Ablation is recommended as a definitive treatment. During this minimally invasive procedure, radiofrequency energy or cryoablation (freezing) is delivered through a catheter to destroy the small, abnormal electrical pathway responsible for the short circuit. This procedure offers a high success rate, often exceeding 90%, and can effectively cure the condition.