Supraventricular Tachycardia (SVT) - Description & Treatment for Patients

Description:

Supraventricular Tachycardia (SVT) refers to a group of arrhythmias that originate above the ventricles (hence "supraventricular"). SVT is characterized by an abnormally fast heart rate, typically greater than 100 beats per minute, and a narrow QRS complex on an electrocardiogram (ECG). It is caused by abnormal electrical circuits in the atria or AV node.

SVT can be intermittent (paroxysmal) or sustained, and its onset and termination can be sudden. Although not always life-threatening, SVT can lead to significant symptoms, especially if the rate is very fast.

  • Mechanism of SVT:

    • Reentry Circuits: The most common cause of SVT is a reentrant circuit, where the electrical impulse continuously travels through a loop, stimulating the heart to beat rapidly.

    • Automaticity: Some forms of SVT are caused by abnormal automatic electrical activity (e.g., atrial tachycardia).

  • Types of SVT:

    • Atrioventricular Nodal Reentrant Tachycardia (AVNRT): The most common form of SVT, caused by a reentry circuit involving the AV node.

    • Atrioventricular Reentrant Tachycardia (AVRT): Caused by an accessory pathway (such as in Wolff-Parkinson-White Syndrome) that allows electrical signals to bypass the AV node.

    • Atrial Tachycardia (AT): Occurs when an abnormal electrical focus in the atria leads to rapid atrial beats.

    • Sinus Tachycardia: Although it involves the normal sinoatrial (SA) node, it can sometimes be categorized as SVT if the rate is excessively fast due to an external trigger (e.g., fever, stress, anemia).

  • Causes of SVT:

    • Structural Heart Disease: Including atrial enlargement, heart failure, or valvular disease.

    • Congenital Heart Disease: Particularly accessory pathways (in AVRT or WPW syndrome).

    • Stimulants: Caffeine, alcohol, or certain medications (e.g., decongestants or beta-agonists).

    • Electrolyte Imbalances: Low potassium, magnesium, or calcium.

    • Thyroid Disorders: Hyperthyroidism can trigger SVT.

    • Increased Sympathetic Tone: Stress, anxiety, or exercise.

    • Idiopathic: In some cases, the exact cause may not be identified.

Symptoms of SVT:

  • Palpitations (a feeling of rapid, pounding, or fluttering heartbeats)

  • Dizziness or lightheadedness

  • Shortness of breath

  • Chest pain (in some cases)

  • Fatigue

  • Syncope (fainting) in severe cases, especially with very high rates

Treatment for Patients:

The management of SVT depends on whether the patient is stable (no signs of hemodynamic compromise) or unstable (with symptoms such as hypotension or syncope). The main goals are to control the heart rate, terminate the arrhythmia, and prevent recurrence.

1. For Stable SVT (Without Hemodynamic Instability):

Goal: To slow the heart rate and convert the arrhythmia to normal sinus rhythm.

  • Vagal Maneuvers:

    • Valsalva Maneuver: Involves bearing down as if to have a bowel movement. This increases pressure in the chest, stimulating the vagus nerve and slowing the heart rate.

    • Carotid Sinus Massage: Performed by a trained professional, this can stimulate the vagus nerve and slow conduction through the AV node.

    • Cold Water Splash: Splashing cold water on the face may also stimulate the vagus nerve.

  • Pharmacological Treatment:

    • Adenosine: A first-line drug for acute management of SVT, especially AVNRT and AVRT. It works by temporarily blocking the AV node, which can interrupt the reentry circuit and restore normal rhythm. Typically administered as a rapid intravenous (IV) bolus.

    • Beta-blockers: Medications like Metoprolol or Atenolol help control the heart rate by reducing sympathetic tone and slowing AV nodal conduction.

    • Calcium Channel Blockers: Diltiazem or Verapamil are effective in slowing the heart rate, especially in cases of AVNRT or atrial tachycardia.

    • Digoxin: In some cases, particularly in older patients with heart failure, digoxin may be used to control rate, but it is generally less effective than beta-blockers or calcium channel blockers.

  • Electrical Cardioversion:

    • If pharmacologic treatments and vagal maneuvers fail, or if the patient remains symptomatic, synchronized electrical cardioversion may be used to restore normal rhythm. This is typically reserved for more persistent or refractory cases.

2. For Unstable SVT (With Hemodynamic Instability):

Goal: Immediate treatment to stabilize the patient and restore normal rhythm.

  • Immediate Synchronized Cardioversion:

    • For patients who are hemodynamically unstable (e.g., hypotension, chest pain, or syncope), immediate synchronized cardioversion is the treatment of choice. This involves delivering a synchronized electrical shock to the heart to reset the rhythm.

    • Energy settings: Typically, 50-100 joules are used initially, with adjustments made if the rhythm is not restored after the first shock.

  • Advanced Cardiac Life Support (ACLS):

    • If the patient becomes more critically ill (e.g., no pulse or loss of consciousness), ACLS protocols should be followed, including CPR and defibrillation if required.

3. Chronic Management (Prevention of Recurrence):

For patients with recurrent SVT or those who have persistent symptoms despite initial treatment, long-term management is necessary.

  • Antiarrhythmic Medications:

    • Beta-blockers (e.g., Metoprolol) or Calcium Channel Blockers (e.g., Diltiazem) are commonly used for long-term rate control, especially in patients with AVNRT or AVRT.

    • Flecainide or Propafenone may be used in patients with atrial tachycardia or those without significant structural heart disease.

  • Catheter Ablation:

    • Catheter ablation is often the definitive treatment for patients with recurrent or persistent SVT. It is particularly effective for conditions like AVNRT, AVRT, and some cases of atrial tachycardia. During the procedure, a catheter is inserted into the heart to target and destroy the abnormal electrical pathway causing the arrhythmia.

    • Ablation has a high success rate and can be considered for patients who have frequent or severe episodes of SVT or those who are not responsive to medications.

  • Lifestyle Modifications:

    • Avoiding triggers: Identifying and avoiding triggers such as excessive caffeine, alcohol, or stimulants.

    • Stress management: Techniques like meditation, yoga, or cognitive behavioral therapy (CBT) may help reduce episodes of SVT, especially if they are stress-induced.

  • Electrolyte Management:

    • Correcting electrolyte imbalances, especially low potassium or magnesium, can help prevent recurrent SVT episodes.

4. Long-Term Monitoring:

  • Regular Follow-up: For patients with recurrent SVT, follow-up with a cardiologist is important to monitor the effectiveness of treatment, the need for ablation, and the risk of other heart conditions.

  • Electrophysiology Studies: In some cases, further electrophysiological studies may be done to assess the specific cause of SVT and guide treatment decisions.

Summary:

Supraventricular Tachycardia (SVT) is a fast and regular arrhythmia that originates above the ventricles. Treatment includes acute measures to slow the heart rate and terminate the arrhythmia, with adenosine being the first-line drug in many cases. If the patient is unstable, electrical cardioversion is performed. Long-term management can involve antiarrhythmic medications, catheter ablation for recurrent or persistent SVT, and lifestyle modifications to reduce triggers. Early intervention and effective treatment can significantly improve quality of life and reduce symptoms associated with SVT.