Paroxysmal supraventricular tachycardia
Introduction
Paroxysmal supraventricular tachycardia (PSVT) is a type of arrhythmia characterized by episodes of rapid heart rate originating above the ventricles. This condition is often abrupt in onset and termination, leading to a sudden increase in heart rate that can range from 150 to 250 beats per minute. PSVT is a common cardiac arrhythmia and can occur in individuals with or without underlying heart disease. It is important to understand the mechanisms, symptoms, diagnosis, and treatment options associated with PSVT to manage the condition effectively.
Pathophysiology
PSVT occurs due to abnormal electrical conduction pathways in the heart, specifically in the atria or the atrioventricular (AV) node. The most common mechanism is re-entry, where an electrical impulse continuously circulates within a closed loop, causing rapid heartbeats. There are several types of PSVT, including atrioventricular nodal reentrant tachycardia (AVNRT), atrioventricular reentrant tachycardia (AVRT), and atrial tachycardia.
Atrioventricular Nodal Reentrant Tachycardia (AVNRT)
AVNRT is the most prevalent form of PSVT, accounting for approximately 60% of cases. It involves a reentrant circuit within or near the AV node. The AV node has two pathways: a slow pathway and a fast pathway. In AVNRT, an electrical impulse travels down the slow pathway and returns via the fast pathway, creating a loop that results in rapid heartbeats.
Atrioventricular Reentrant Tachycardia (AVRT)
AVRT involves an accessory pathway that connects the atria and ventricles, bypassing the AV node. This accessory pathway, known as the bundle of Kent, can conduct impulses in both directions, leading to a reentrant circuit. AVRT is commonly associated with Wolff-Parkinson-White (WPW) syndrome, where the presence of an accessory pathway predisposes individuals to tachycardia.
Atrial Tachycardia
Atrial tachycardia originates from an ectopic focus within the atria, outside the normal conduction system. This focus generates rapid impulses that override the sinus node, leading to tachycardia. Unlike AVNRT and AVRT, atrial tachycardia does not involve a reentrant circuit.
Clinical Presentation
The clinical presentation of PSVT varies among individuals, but common symptoms include palpitations, dizziness, shortness of breath, chest pain, and fatigue. Some patients may experience anxiety or a feeling of impending doom during an episode. The sudden onset and termination of symptoms are characteristic of PSVT. In severe cases, syncope or near-syncope may occur due to reduced cardiac output.
Diagnosis
The diagnosis of PSVT is primarily based on clinical history and electrocardiogram (ECG) findings. An ECG during an episode typically shows a narrow QRS complex tachycardia, although wide complex tachycardia can occur if there is aberrant conduction. The presence of P waves and their relationship to the QRS complex can help differentiate between types of PSVT.
Electrocardiogram (ECG)
An ECG is crucial for diagnosing PSVT. In AVNRT, P waves are often hidden within or immediately after the QRS complex. In AVRT, a delta wave may be present, indicating pre-excitation. Atrial tachycardia shows P waves preceding each QRS complex, with an abnormal P wave axis.
Electrophysiological Study
In some cases, an electrophysiological study (EPS) is performed to evaluate the conduction pathways and confirm the diagnosis. EPS involves the insertion of catheters into the heart to record electrical activity and induce arrhythmias. This procedure can identify the type of PSVT and guide treatment decisions.
Treatment
The management of PSVT includes acute termination of episodes and long-term prevention of recurrences. Treatment options vary depending on the type of PSVT, the frequency of episodes, and the presence of underlying heart disease.
Acute Management
Acute management aims to terminate the tachycardia and restore normal sinus rhythm. Vagal maneuvers, such as the Valsalva maneuver or carotid sinus massage, can increase vagal tone and interrupt the reentrant circuit. If vagal maneuvers are ineffective, intravenous adenosine is the drug of choice, as it transiently blocks conduction through the AV node.
Pharmacological Therapy
For patients with frequent episodes, pharmacological therapy may be necessary. Beta-blockers and calcium channel blockers are commonly used to prevent recurrences by slowing conduction through the AV node. Antiarrhythmic drugs, such as flecainide or propafenone, may be considered in refractory cases.
Catheter Ablation
Catheter ablation is a definitive treatment option for PSVT, particularly in patients with frequent or symptomatic episodes. This procedure involves the use of radiofrequency energy to ablate the abnormal conduction pathway, thereby preventing reentrant circuits. Catheter ablation has a high success rate and is considered safe and effective.
Prognosis
The prognosis for individuals with PSVT is generally favorable, especially with appropriate management. While PSVT can cause significant symptoms, it is rarely life-threatening. Catheter ablation offers a potential cure, significantly improving the quality of life for many patients. However, some individuals may experience recurrences or develop other arrhythmias over time.
Epidemiology
PSVT affects individuals of all ages, with a higher prevalence in women. The incidence of PSVT increases with age, and it is more common in those with a history of heart disease. While PSVT can occur in healthy individuals, certain risk factors, such as hypertension, hyperthyroidism, and structural heart abnormalities, can predispose individuals to this arrhythmia.
Complications
Although PSVT is generally benign, complications can arise, particularly in individuals with underlying heart disease. Prolonged episodes of tachycardia can lead to hemodynamic instability, heart failure, or myocardial ischemia. In rare cases, PSVT can degenerate into more serious arrhythmias, such as atrial fibrillation or ventricular tachycardia.