What causes svt heart

What is Supraventricular Tachycardia (SVT)?

Supraventricular tachycardia, commonly known as SVT, refers to a group of heart rhythm disorders (arrhythmias) that cause a rapid heartbeat. The term 'supraventricular' indicates that the rapid rhythm originates in the upper chambers of the heart, known as the atria, or in the area where the atria connect to the ventricles, specifically the atrioventricular (AV) node. This electrical disturbance bypasses the normal, controlled pathway of electrical conduction, leading to a heart rate that is significantly faster than normal, typically ranging from 100 to 200 beats per minute, and sometimes even higher (up to 250 bpm).

The heart's normal rhythm is controlled by electrical impulses that originate in the sinus node, the heart's natural pacemaker, located in the right atrium. These impulses travel through the atria, causing them to contract, and then pass through the AV node. The AV node acts as a gatekeeper, slowing down the impulse slightly to allow the ventricles to fill with blood before they contract and pump blood to the rest of the body. In SVT, however, there is an electrical 'short circuit' or an extra electrical pathway that causes the impulses to travel too quickly or in a loop, resulting in the rapid heart rate.

What Causes SVT?

The underlying cause of SVT is an abnormality in the heart's electrical system. This can manifest in several ways:

1. Reentrant Pathways

The most common cause of SVT involves a reentrant pathway. This is essentially an electrical loop or short circuit. Normally, electrical impulses travel in one direction. In reentrant SVT, an impulse travels down one pathway and then returns up another, creating a continuous loop that stimulates the heart to beat very rapidly. There are a few types of reentrant SVTs:

• Atrioventricular Reentrant Tachycardia (AVRT): This is the most common type of SVT, accounting for approximately 65% of cases. It occurs when there is an extra electrical connection (an accessory pathway) between the atria and ventricles, in addition to the normal AV node pathway. The electrical impulse can travel down the AV node and up the accessory pathway, or vice versa, creating a loop.
• Atrioventricular Nodal Reentrant Tachycardia (AVNRT): This type involves a 'dual pathway' within the AV node itself. The electrical impulse can travel down one pathway and back up the other within the AV node, creating a rapid, continuous circuit. This is the second most common type of SVT.
• Intra-atrial Reentrant Tachycardia (IART): Less common than AVRT and AVNRT, this involves a reentrant circuit within the atria themselves, often related to scarring from previous heart surgery or disease.

2. Abnormal Automaticity

In some cases, SVT can be caused by an issue with the heart's natural pacemaker cells (automaticity). Normally, the sinus node controls the heart rate. However, in certain conditions, other cells in the atria or AV node can become hyperactive and fire electrical impulses much faster than the sinus node, leading to a rapid heart rate. This is less common than reentrant SVT.

3. Wolff-Parkinson-White (WPW) Syndrome

WPW syndrome is a condition where individuals are born with an extra electrical pathway (an accessory pathway) that bypasses the AV node. This pathway can lead to AVRT, the most common form of SVT. While many people with WPW syndrome never experience symptoms, others can develop episodes of rapid heart rate.

4. Congenital Heart Defects

Some individuals born with structural heart problems (congenital heart defects) may have an increased risk of developing SVT due to abnormalities in the heart's electrical pathways.

5. Other Contributing Factors and Triggers

While the primary cause is an electrical abnormality, certain factors and triggers can provoke an episode of SVT in susceptible individuals:

• Stress and Anxiety: Emotional stress can trigger the release of hormones that affect heart rate.
• Caffeine and Stimulants: Consumption of coffee, tea, energy drinks, or other caffeinated beverages can sometimes initiate SVT.
• Alcohol: Excessive alcohol intake, particularly binge drinking, is a known trigger for arrhythmias.
• Smoking: Nicotine is a stimulant that can affect heart rhythm.
• Certain Medications: Some medications, including decongestants, asthma inhalers, and thyroid medications, can increase heart rate or trigger SVT.
• Fatigue and Lack of Sleep: Being overly tired can sometimes lead to arrhythmias.
• Dehydration: Significant fluid loss can affect electrolyte balance and heart function.
• Illness: Fever or infections can sometimes trigger SVT episodes.
• Pregnancy: Hormonal changes and increased blood volume during pregnancy can sometimes lead to SVT.
• Underlying Heart Disease: While SVT can occur in people with healthy hearts, conditions like coronary artery disease, heart valve problems, or heart failure can increase the risk or make episodes more frequent.
• Thyroid Disorders: An overactive thyroid (hyperthyroidism) can accelerate heart rate and contribute to SVT.

Symptoms of SVT

The symptoms of SVT can vary widely among individuals and even from episode to episode in the same person. Common symptoms include:

• Sudden onset of a rapid heartbeat (palpitations)
• Dizziness or lightheadedness
• Shortness of breath
• Chest discomfort or pain
• Anxiety
• Fainting (syncope)
• Fatigue

Episodes can be brief, lasting only a few minutes, or they can persist for several hours. The rapid heart rate can make it difficult for the heart to pump blood efficiently, leading to the associated symptoms.

Diagnosis and Treatment

Diagnosis typically involves an electrocardiogram (ECG or EKG) to record the heart's electrical activity. Holter monitors or event recorders may be used for longer-term monitoring. Treatment depends on the frequency and severity of symptoms and may include vagal maneuvers (like bearing down), medications, or procedures like catheter ablation to correct the electrical short circuit.