Supraventricular tachycardia

Overview

Supraventricular tachycardia (SVT) is an abnormal, rapid heart rhythm that starts in the upper chambers of the heart, called the atria. In a normal heart, electricity travels from the atria, through the atrioventricular (AV) node to the lowers chambers, called the ventricles. This transmission produces a regular heartbeat of 60 to 100 times per minute. In SVT, the heart beats too quickly — up to 300 beats per minute — preventing the heart from filling completely with blood. As a result, the body doesn't receive the blood volume it needs to function properly.

There are many different forms of SVT, including:

• Atrial fibrillation, the most common SVT, occurs when multiple sites in the atria fire impulses in an irregular fashion. As a result, the heart can beat very quickly and ineffectively.
• Atrial flutter is a rapid heart rhythm caused by an extra electrical pathway in the heart that begins in the atria. This causes a very fast, steady heartbeat.
• Atrioventricular nodal reentrant tachycardia (AVNRT), the second most comman type of SVT, occurs when there is an extra electrical pathway in the AV node.
• Atrial tachycardia is an abnormal rhythm that arises in the atria.
• Wolff-Parkinson-White syndrome is an abnormal electrical connection between the atria and ventricles. This pathway is known as an accessory pathway and may result in a very rapid heartbeat.

Signs & symptoms

Supraventricular Tachycardia may cause the following symptoms:

• Chest pressure or pain
• Fainting, also known as syncope, or near-syncope
• Fatigue
• Lightheadedness or dizziness
• Palpitations, which can be skipping, fluttering or pounding in the chest
• Shortness of breath

Diagnosis

Supraventricular tachycardia may occur spontaneously with unpredictable timing. Therefore, in many cases, the condition requires specialized tests to acquire an accurate diagnosis. If your doctor suspects that your child has an arrhythmia, one or more of the following diagnostic tests will be ordered to determine the source of your child's symptoms.

• Electrocardiogram (ECG or EKG) — An ECG records the heart's electrical activity. Small patches called electrodes are placed on your child's chest, arms and legs, and are connected by wires to the ECG machine. The electrical impulses of your child's heart are translated into a graph or chart, enabling doctors to determine the pattern of electrical current flow in the heart and to diagnose arrhythmias.
• Electrophysiology (EP) Study — In an EP study, doctors insert special electrode catheters — long, flexible wires — into veins and guide them into the heart. These catheters sense electrical impulses and also may be used to stimulate different areas of the heart. Doctors can then locate the sites that are causing arrhythmias. The EP study allows doctors to examine an arrhythmia under controlled conditions and acquire more accurate, detailed information than with any other diagnostic test.
• Exercise Stress Test — An exercise stress or treadmill test records the electrical activity of your child's heart during exercise, which differs from the heart's electrical activity at rest.
• Event Monitor — This is a small monitor about the size of a pager that your child can have for up to a month. Since the arrhythmia may occur at unpredictable times, this will help to record the abnormal rhythm when your child is experiencing symptoms. He or she can just push a button on the pager and record the heartbeat. The recording can then be transmitted by phone to the doctor.
• Holter Monitor — A Holter monitor is a small, portable machine that your child wears for 24 hours. It is about the size of a portable tape player and provides a continuous 24-hour recording of your child's heartbeat onto a tape. You will be asked to keep a diary of your child's activities and symptoms. This monitor may detect arrhythmias that might not show up on a resting electrocardiogram, which only records a heartbeat for a few seconds at rest.

Treatment

The treatment for your child's supraventricular tachycardia (SVT) will depend on the type and severity of their condition and the results of various diagnostic tests, such as the electrophysiology (EP) study. You and your doctor will decide which treatment is right for your child.

The following treatments may be considered:

Medications

Certain anti-arrhythmic drugs change the electrical signals in the heart and help prevent heart abnormalities from starting irregular or rapid heart rhythms. Medication may be used to convert SVT to a normal rhythm, slow down the heart rate or prevent recurrences. Our goal is to find the medication that works best for your child. On occasion, we admit children to the hospital and monitor their heart rhythm while we start the medication.

Radiofrequency Catheter Ablation (RFA)

Radiofrequency catheter ablation (RFA) is a technique to treat arrhythmia that was pioneered at UCSF. It disrupts part of the electrical pathway causing irregular heart rhythms, providing relief for patients who may not respond well to medications, who prefer not to take medications or who can't take medications.

The procedure involves threading a tiny metal-tipped catheter through a vein or artery in the leg and into the heart. Using fluoroscopy or X-ray, doctors guide the catheter through a blood vessel to the heart. Additional catheters, inserted through the vein in the leg and the neck, contain electrical sensors to find the area causing the arrhythmia. This is called mapping.

The metal-tipped catheter is maneuvered to each site in the heart that causes the irregular heartbeat. Radiofrequency waves or current is sent through the tip of the catheter, cauterizing or burning cells to destroy the extra electrical pathways that cause abnormal heart rhythms. In most cases, patients leave the hospital within 24 hours or the same day.

RFA has been proven very effective in treating children with arrhythmias. Your doctor will discuss this treatment and others with you to decide the best option for you or your child. For conditions like Wolff-Parkinson-White syndrome, in which a hair-thin strand of tissue creates an extra electrical pathway between the upper and lower chambers of the heart, RFA ablation offers a cure. It has become the treatment of choice for patients with that disorder.

Cryoablation

Sometimes referred to as cryo, cryoablation is similar to radiofrequency catheter ablation (RFA) in that it is a procedure that disrupts the abnormal electrical pathway in the heart. This newer technology has been used in the Electrophysiology Laboratory at UCSF Benioff Children's Hospital since March 2004.

Instead of burning cells, however, cryoablation destroys cells by freezing them and has been very effective in treating children with arrhythmias. Your doctor will discuss this treatment and others with you to decide which method is the best option.

Like RFA, cryoablation involves threading a tiny metal-tipped catheter through a vein or artery in the leg and into the heart. Doctors guide the catheter through the blood vessel to the heart by using fluoroscopy or X-ray.