Supraventricular Tachycardia (SVT)

Supraventricular Tachycardia (SVT) refers to a group of abnormal heart rhythms (arrhythmias) that originate above the ventricles, specifically in the atria (the heart’s upper chambers) or the AV node (the junction between the atria and ventricles). In SVT, the heart beats abnormally fast—often over 100 beats per minute—but the rhythm remains regular. SVT can occur in people with otherwise healthy hearts, but it may also be associated with certain heart conditions.

Key Features of Supraventricular Tachycardia (SVT):

1. Origin: SVT originates above the ventricles, either in the atria or at the AV node, the electrical pathway between the atria and the ventricles.

2. Rapid Heart Rate: The heart rate in SVT is typically above 100 bpm (beats per minute), but it can range from 150-250 bpm, depending on the type of SVT.

3. Regular Rhythm: In most forms of SVT, the heart rhythm is regular, but very fast.

4. Episodes: SVT can come on suddenly (called paroxysmal SVT) and can last for seconds, minutes, or even hours, but it usually stops on its own.

Symptoms of SVT:

SVT episodes may cause the following symptoms:

• Palpitations: A sensation of a fast or irregular heartbeat, often described as a fluttering or pounding in the chest.

• Dizziness or lightheadedness: Due to the rapid heart rate not allowing the heart to fill properly with blood.

• Shortness of breath: Difficulty breathing due to the heart’s reduced ability to pump blood effectively.

• Chest discomfort: A feeling of pressure or pain in the chest, which may be more noticeable during an SVT episode.

• Fainting (syncope): In severe cases, the fast heart rate may reduce blood flow to the brain, causing fainting.

In many cases, SVT is not dangerous and can be managed with medications or lifestyle changes, but in more severe cases, it can lead to complications like heart failure or stroke if left untreated.

Types of SVT:

There are several different types of SVT, each with its own underlying cause and mechanism:

1. Atrioventricular Nodal Reentrant Tachycardia (AVNRT):

   • This is the most common type of SVT. It occurs due to an abnormal electrical pathway in or near the AV node that causes the electrical impulses to loop back on themselves, leading to a rapid heartbeat.

   • Symptoms: Sudden onset of palpitations, dizziness, or fainting. It often occurs in young and otherwise healthy people.

2. Atrioventricular Reentrant Tachycardia (AVRT):

   • In AVRT, there is an extra electrical pathway between the atria and ventricles, which can form a reentrant circuit. This pathway bypasses the normal conduction system, leading to a rapid heartbeat.

   • This is commonly associated with Wolff-Parkinson-White (WPW) syndrome, a condition in which an accessory pathway exists that can lead to episodes of rapid heart rate.

   • Symptoms: Similar to AVNRT, including sudden palpitations, dizziness, and shortness of breath.

3. Atrial Tachycardia (AT):

   • This occurs when abnormal electrical impulses arise from the atria (the upper chambers of the heart), leading to rapid atrial contractions.

   • Unlike AVNRT and AVRT, the abnormal electrical activity originates in the atria rather than the AV node or accessory pathway.

   • Symptoms: Similar to other forms of SVT, but it may have a slightly different rhythm on the ECG (often less regular than AVNRT or AVRT).

4. Sinus Tachycardia:

   • Sinus tachycardia is a normal increase in heart rate, often occurring in response to stress, fever, exercise, or caffeine. Although it is not technically considered an arrhythmia, it is sometimes grouped with SVT because the heart rate is elevated, and it involves the sinus node (the heart’s natural pacemaker).

   • Symptoms: This can cause palpitations, but it is generally less concerning than other forms of SVT because the rhythm is usually normal.

5. Multifocal Atrial Tachycardia (MAT):

   • This form of SVT involves multiple sites in the atria generating abnormal electrical impulses, leading to a rapid heart rate with multiple different P waves on the ECG.

   • It is more commonly seen in patients with lung disease, such as COPD (chronic obstructive pulmonary disease).

   • Symptoms: This type of tachycardia can cause palpitations, shortness of breath, and sometimes fatigue or dizziness.

Diagnosis of SVT:

To diagnose SVT, healthcare providers rely on the following:

• Electrocardiogram (ECG): The ECG is the primary tool for diagnosing SVT. It shows the rapid and regular heart rate, with different features depending on the type of SVT:

  • AVNRT: A short PR interval and a regular rhythm with a narrow QRS complex.

  • AVRT: A characteristic delta wave (if associated with WPW syndrome) and a short PR interval.

  • Atrial tachycardia: Abnormal P waves originating from the atria.

• Holter monitor: A 24-hour or longer ECG recording can help capture episodes of SVT and provide more information about the rhythm.

• Electrophysiology study (EPS): In some cases, a catheter-based study may be needed to map the electrical pathways of the heart and pinpoint the cause of the SVT.

Treatment of SVT:

The treatment approach for SVT depends on the frequency and severity of episodes, as well as the underlying cause.

1. Vagal Maneuvers:

   • In cases of paroxysmal (sudden) SVT, simple maneuvers like bearing down (Valsalva maneuver) or cold water immersion can stimulate the vagus nerve, which can slow the heart rate and potentially terminate the episode of SVT. These are often the first steps to try before seeking medical help.

2. Medications:

   • Adenosine: This is often used in emergency settings to rapidly terminate an episode of SVT. It works by briefly blocking the AV node and stopping the abnormal electrical circuit.

   • Beta-blockers or calcium channel blockers: These medications are often used to slow down the heart rate and prevent further episodes of SVT.

   • Antiarrhythmic drugs: If episodes are frequent or hard to control, drugs like flecainide or amiodarone may be used to prevent recurrence.

3. Electrical Cardioversion:

   • In rare cases where the SVT does not respond to medications or vagal maneuvers, or if the patient is hemodynamically unstable (e.g., low blood pressure or chest pain), electrical cardioversion (a controlled shock to the heart) may be used to restore normal rhythm.

4. Catheter Ablation:

   • For patients with recurrent SVT or who do not respond well to medications, catheter ablation may be recommended. During this procedure, a catheter is inserted into the heart via blood vessels, and the abnormal electrical pathways responsible for the SVT are destroyed with radiofrequency energy or cryotherapy.

   • Ablation is highly effective and often curative for conditions like AVNRT and AVRT, with success rates over 90%.

5. Lifestyle Modifications:

   • Avoiding stimulants like caffeine, alcohol, or recreational drugs can help reduce the likelihood of SVT episodes.

   • Managing stress and maintaining a healthy lifestyle can also be beneficial in reducing triggers for SVT.

Prognosis:

SVT is often not dangerous and can be well-managed with medications, vagal maneuvers, or ablation. However, if left untreated, frequent or sustained SVT can lead to complications like heart failure due to the heart working too hard to keep up with the rapid rhythm. In rare cases, SVT can progress to more serious arrhythmias like ventricular tachycardiaor fibrillation, especially in individuals with underlying heart disease.

Summary:

• Supraventricular Tachycardia (SVT) is a group of fast, regular heart rhythms that originate above the ventricles, either in the atria or the AV node.

• SVT episodes can cause symptoms like palpitations, dizziness, shortness of breath, or fainting, but they are often not life-threatening.

• Diagnosis is based on an ECG, and treatment includes vagal maneuvers, medications, electrical cardioversion, and catheter ablation.

• While SVT is often manageable, ablation can be curative for many patients with frequent episodes or those who do not respond to medications.

If you have any further questions about SVT or need clarification on any point, feel free to ask!