Supraventricular tachycardia

Overview

Supraventricular tachycardia (SVT) is a rapid heart rhythm originating above the ventricles. This condition is characterized by an abnormally fast heartbeat, typically exceeding 100 beats per minute, which can lead to symptoms such as palpitations, dizziness, shortness of breath, and chest pain. SVT encompasses a variety of arrhythmias, including atrial fibrillation, atrial flutter, and atrioventricular nodal reentrant tachycardia (AVNRT).

Pathophysiology

SVT arises from abnormal electrical activity in the heart's atria or the atrioventricular (AV) node. The heart's electrical system includes the sinoatrial (SA) node, AV node, and the His-Purkinje system. In SVT, the electrical impulses are either generated inappropriately or follow abnormal pathways, leading to rapid heart rates. The reentrant circuit, a common mechanism in SVT, involves a loop of electrical activity that perpetuates the rapid rhythm.

Types of Supraventricular Tachycardia

Atrial Fibrillation

Atrial fibrillation (AF) is the most common type of SVT. It is characterized by disorganized electrical activity in the atria, leading to an irregular and often rapid heart rate. AF can be paroxysmal, persistent, or permanent. Risk factors include hypertension, heart failure, and valvular heart disease.

Atrial Flutter

Atrial flutter involves a rapid but regular atrial rhythm, typically around 250-350 beats per minute. It is often associated with a 2:1 conduction ratio, meaning the ventricles beat at half the atrial rate. Atrial flutter can coexist with atrial fibrillation and shares similar risk factors.

Atrioventricular Nodal Reentrant Tachycardia (AVNRT)

AVNRT is a common form of SVT, particularly in younger individuals. It involves a reentrant circuit within or near the AV node, leading to a rapid and regular heart rate. Symptoms often include palpitations, lightheadedness, and syncope.

Atrioventricular Reentrant Tachycardia (AVRT)

AVRT involves an accessory pathway that bypasses the AV node, creating a reentrant circuit. The most well-known form is Wolff-Parkinson-White (WPW) syndrome, characterized by a short PR interval and delta wave on the ECG. AVRT can lead to very rapid heart rates and is often triggered by premature atrial contractions.

Diagnosis

The diagnosis of SVT involves a thorough clinical evaluation, including a detailed medical history and physical examination. Electrocardiography (ECG) is the primary diagnostic tool, revealing characteristic patterns for different types of SVT. Holter monitoring, event recorders, and electrophysiological studies may be used for further evaluation.

Management

Acute Management

The acute management of SVT focuses on terminating the arrhythmia and stabilizing the patient. Vagal maneuvers, such as the Valsalva maneuver or carotid sinus massage, can be effective in terminating certain types of SVT. Intravenous adenosine is often used for its rapid action in terminating reentrant tachycardias. Other medications, such as beta-blockers and calcium channel blockers, may also be used.

Long-term Management

Long-term management of SVT aims to prevent recurrence and manage underlying conditions. Antiarrhythmic medications, such as flecainide, propafenone, and amiodarone, may be prescribed. Catheter ablation is an effective and often curative treatment for many types of SVT, particularly AVNRT and AVRT. Lifestyle modifications, such as reducing caffeine and alcohol intake, can also help manage symptoms.

Prognosis

The prognosis for individuals with SVT varies depending on the type and underlying cause. Many forms of SVT, particularly those amenable to catheter ablation, have an excellent prognosis with appropriate treatment. However, conditions like atrial fibrillation may require ongoing management and carry a risk of complications such as stroke and heart failure.

Epidemiology

SVT is a common arrhythmia, affecting individuals of all ages. The prevalence increases with age, and certain types, such as AVNRT, are more common in younger populations. Risk factors include structural heart disease, hypertension, and genetic predisposition.

Complications

Complications of SVT can include heart failure, myocardial ischemia, and thromboembolic events. Atrial fibrillation, in particular, is associated with an increased risk of stroke, necessitating anticoagulation therapy in many patients.

Research and Future Directions

Ongoing research in SVT focuses on improving diagnostic techniques, developing new antiarrhythmic drugs, and refining catheter ablation procedures. Advances in genetic research may also lead to better understanding and management of inherited forms of SVT.

References