What causes svt heart rate

What is Supraventricular Tachycardia (SVT)?

Supraventricular tachycardia, commonly known as SVT, is a condition characterized by an abnormally fast heart rate originating in the atria, the heart's upper chambers. Normally, the heart beats between 60 and 100 times per minute at rest. In SVT, however, the heart rate can suddenly jump to anywhere from 150 to 220 beats per minute, or even higher. This rapid heartbeat is usually brief, lasting for a few seconds, minutes, or sometimes longer, and then returns to a normal rhythm on its own.

The term "supraventricular" means "above the ventricles," referring to the origin of the rapid electrical impulses in the atria or the atrioventricular (AV) node, which connects the atria to the ventricles. This is in contrast to ventricular tachycardia, which originates in the lower chambers of the heart (ventricles).

What Causes SVT Heart Rate?

The primary cause of SVT is an issue with the heart's electrical system. Specifically, it often involves an abnormal electrical pathway or a "short circuit" that causes the heart to beat too quickly. There are several types of SVT, each with a slightly different electrical anomaly:

1. Atrioventricular Nodal Reentrant Tachycardia (AVNRT)

This is the most common type of SVT, accounting for about 60% of cases. In a healthy heart, electrical impulses travel from the SA node (the heart's natural pacemaker) down through the AV node to the ventricles in a one-way street. In AVNRT, there are typically two electrical pathways within or near the AV node. One pathway conducts impulses faster than the other. When an impulse reaches the AV node, it can enter the slower pathway, travel down to the ventricle, and then loop back up through the faster pathway, creating a continuous circuit. This circuit causes the atria and ventricles to beat very rapidly.

2. Atrioventricular Reentrant Tachycardia (AVRT)

This type of SVT involves an accessory pathway, which is an extra electrical connection between the atria and ventricles that exists from birth. This pathway bypasses the AV node. In the most common form of AVRT (orthodromic AVRT), the impulse travels down the normal AV node pathway and then loops back up to the atria via the accessory pathway, creating a re-entrant circuit. Less commonly, the impulse travels down the accessory pathway and back up the AV node (antidromic AVRT), which usually results in a wider QRS complex on an ECG.

3. Ectopic Atrial Tachycardia (EAT)

In EAT, a single focus (a small area) within the atria generates electrical impulses at a very rapid rate, overriding the SA node. This focus might be located in a specific part of the atrium or originate from the pulmonary veins, which connect to the left atrium.

4. Junctional Tachycardia

This occurs when the AV junction, the area connecting the atria and ventricles, becomes the site of rapid electrical firing. It can be a normal response to stress or illness, or it can be pathological.

Factors That Can Trigger SVT Episodes

While the underlying cause of SVT is an electrical anomaly, certain factors can trigger an episode of rapid heart rate in susceptible individuals. These triggers are not the cause of the condition itself but can initiate the abnormal electrical activity. Common triggers include:

• Stress and anxiety
• Caffeine intake
• Alcohol consumption
• Smoking
• Certain medications (e.g., decongestants, asthma inhalers)
• Fatigue or lack of sleep
• Illness or fever
• Sudden physical exertion or changes in posture
• Pregnancy
• Certain electrolyte imbalances

When to Seek Medical Attention

Occasional, brief episodes of SVT that resolve on their own with no other symptoms may not require immediate medical attention. However, you should seek medical advice if:

• Your SVT episodes are frequent or prolonged.
• You experience other symptoms along with the rapid heart rate, such as chest pain, shortness of breath, dizziness, lightheadedness, fainting (syncope), or palpitations.
• You have a known heart condition or risk factors for heart disease.

A doctor can diagnose SVT through a physical examination, listening to your heart, and performing an electrocardiogram (ECG). Sometimes, further tests like a Holter monitor or an event recorder may be needed to capture an episode. Treatment depends on the type and frequency of SVT and may include vagal maneuvers, medications, or, in some cases, catheter ablation.