SVT Quiz

Supraventricular Tachycardia (SVT): Core Concepts for Clinical Review

Supraventricular Tachycardia refers to a group of abnormally fast heart rhythms that originate above the ventricles. Mastering SVT involves understanding its various types, recognizing key ECG patterns, and knowing the tiered treatment approach based on patient stability.

Defining Supraventricular Tachycardia

SVT is characterized by a heart rate typically over 150 beats per minute. The critical feature is its origin: the electrical impulse begins at or above the atrioventricular (AV) node. This results in a narrow QRS complex (<0.12 seconds) on an ECG because the ventricular conduction pathway remains normal.

Major Types of SVT

While SVT is a broad category, a few types are most common in clinical practice and on exams. Focus on differentiating Atrioventricular Nodal Reentrant Tachycardia (AVNRT), Atrioventricular Reentrant Tachycardia (AVRT), and Atrial Tachycardia. AVNRT is the most frequent form, involving a reentrant circuit within the AV node itself.

ECG Recognition: The Narrow-Complex Tachycardia

The hallmark of most SVTs is a regular, narrow-complex tachycardia. For exam questions, the first step is to identify QRS duration. If it’s narrow, SVT is a primary differential. P waves are often difficult to identify; they may be absent, inverted after the QRS (retrograde), or buried within it.

Stable vs. Unstable Patient Assessment

The single most important decision point in SVT management is assessing hemodynamic stability. An unstable patient presents with signs of poor perfusion, such as hypotension, altered mental status, signs of shock, or severe chest pain. This distinction dictates the immediate treatment algorithm.

• Stable Patient: Alert, adequate blood pressure, no severe symptoms. Treatment can proceed in a stepwise manner.
• Unstable Patient: Hypotensive, confused, diaphoretic, ischemic chest pain. Requires immediate intervention to restore rhythm.

First-Line Treatment: Vagal Maneuvers

For a stable patient, vagal maneuvers are always the first step. These techniques increase parasympathetic tone, which slows conduction through the AV node and can terminate reentrant tachycardias. The most common and effective method is the modified Valsalva maneuver (straining followed by repositioning).

Pharmacologic Intervention: Adenosine

If vagal maneuvers fail in a stable patient, intravenous adenosine is the drug of choice. It acts by temporarily blocking the AV node, which interrupts the SVT circuit. It has a very short half-life (seconds), making it relatively safe. Be prepared for a transient period of asystole on the monitor after administration.

Managing the Unstable Patient: Synchronized Cardioversion

An unstable patient with SVT is a medical emergency. The treatment is immediate synchronized electrical cardioversion. This procedure delivers a low-energy shock that is timed with the R wave of the QRS complex to depolarize the heart and allow the normal sinus rhythm to resume. Do not delay this for drug therapy.

Long-Term Management Strategies

For patients with recurrent, symptomatic SVT, long-term management is necessary. Options include daily medication (beta-blockers or calcium channel blockers) or a curative procedure. Catheter ablation, which uses radiofrequency energy to destroy the abnormal electrical pathway, has a high success rate and is often the preferred solution.

• Catheter Ablation: Targets the slow pathway in AVNRT or the accessory pathway in AVRT.
• Beta-Blockers (e.g., Metoprolol): Slows heart rate and AV nodal conduction.
• Calcium Channel Blockers (e.g., Verapamil, Diltiazem): Similar mechanism to beta-blockers regarding AV node.
• Antiarrhythmics (e.g., Flecainide): Less common, used for refractory cases.
• Lifestyle Changes: Reducing caffeine, alcohol, and stress can help some individuals.

Key Takeaways

• SVT originates above the ventricles, leading to a narrow-QRS tachycardia.
• The most crucial initial assessment is determining if the patient is hemodynamically stable or unstable.
• Treatment for stable SVT follows a sequence: vagal maneuvers first, then adenosine.
• Unstable SVT requires immediate synchronized electrical cardioversion.
• Catheter ablation is a highly effective curative option for recurrent SVT.

This content is for informational and educational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.