Supraventricular tachycardia


Supraventricular tachycardia

Description, Causes and Risk Factors:

The heart has four chambers - two atria and two ventricles. The walls of these chambers are made mainly of special heart muscle. Each heartbeat starts with a tiny electrical impulse produced by the sinoatrial node (SA node). This node is like a tiny timer or pacemaker at the top of the right atrium. The electrical impulse spreads through the heart muscle and makes it contract (squeeze). The electrical impulse travels first through the atria. These contract and pump blood into the ventricles. The impulse is held up slightly at the atrioventricular node (AV node) which acts like a junction box. Electricity reaches the AV node by two pathways, a fast one from above and a slower one from below. In many people (about 80%) there is very little difference between these two pathways. The electrical impulse then travels through the atrioventricular bundle (AV bundle) which acts like a wire that takes the impulse to the ventricles. This makes the ventricles contract to pump blood into the arteries.

Supraventricular tachycardia (SVT) is a heart condition featuring episodes of an abnormally fast heart rate. The heart will suddenly start racing, then stop or slow down abruptly. Episodes can last for seconds, minutes, hours or (in rare cases) days. They may occur regularly, several times a day, or very infrequently, once or twice a year. The heart rate may be as high as 250 beats per minute, but is usually between 140 and 180 (a normal heartbeat should be 60-100 beats per minute at rest).

In the majority of cases, SVT occurs in people who are born with an extra abnormal electrical connection in the heart. Under certain circumstances, these extra connections can suddenly disrupt the normal electrical patterns within the heart and temporarily establish new electrical patterns that produce the arrhythmia.

In some people, episodes of SVT can be triggered by exercise, stress, gastrointestinal symptoms (such as nausea, vomiting or constipation) or medications. But in most people, SVT appears to occur for no particular reason at all.

Certain medical problems also seem to cause SVT, especially lung disease and hyperthyroidism. The SVT caused by such medical disorders is usually different from the more typical SVT, in that it tends to be more persistent. Adequate treatment usually requires aggressively treating the underlying medical problem.

Risk Factors:

    Affects women more often than men.

  • Most commonly develops in a person's 20s or 30s, but can occur at any age.

  • Occurs more often in people who are anxious, under stress, or physically fatigued.

  • Hyperactive thyroid gland.

  • Excess caffeine or alcohol use.

  • Respiratory illnesses.

  • Low potassium and magnesium levels.

  • Valvular heart disease.

Symptoms:

Children with supraventricular tachycardia (SVT) may feel like their heart is racing or pounding. If their heart cannot pump enough blood and oxygen to their brain, they may feel lightheaded or dizzy. Rarely, children with SVT have no symptoms.

Infants and very young children may not be able to communicate symptoms of SVT. But, in some cases, a caregiver might notice a racing heartbeat.

Diagnosis:

To diagnose this condition, the Cardiologist/PCP will examine your child, check their heartbeat and use a stethoscope to listen to their heart. He/she will ask for details about any symptoms your child has, their health history and your family health history.

SVT tends to happen only once in a while. So it can be hard to diagnose.

To learn about the electrical activity in your child's heart, the doctor will use an electrocardiogram (ECG). If an abnormal heartbeat does not happen during this test, your child may need to wear a portable rhythm-monitoring device for a while.

A device called a Holter monitor can record their heart's activity for 24 hours. Another device, called an event recorder, can be turned on by your child when they feel a problem with their heart rhythm.

To get more information about how your child's heart looks and works, they may need other tests, like chest X-rays, exercise testing, or an echocardiogram.

Treatment:

Acute episodes of SVT almost always stop spontaneously after a few minutes or a few hours. However, many people have learned to stop their episodes by doing something to increase the tone of the vagus nerve. The easiest way to increase your vagal tone is to perform a Valsalva maneuver. A less pleasant method is to initiate the diving reflex by immersing your face in ice water for a few seconds.

If your SVT does not stop within 15 to 30 minutes, or if your symptoms are severe, you should go to the emergency room. You will also want to consider more chronic therapy aimed at preventing recurrent SVT. It is important to keep in mind that SVT is only rarely dangerous (but "merely" symptom-producing). This means there are many options for chronic therapy.

For instance, many people who have only very occasional and time-limited episodes of SVT opt for no specific treatment at all; they simply deal with their episodes as they occur.

In the large majority of cases, SVT can be cured once and for all by an ablation procedure. Most SVTs are caused by extra electrical pathways, and usually those extra pathways can be accurately localized by electrical mapping during an electrophysiology study, and then ablated. Once the extra pathway is gone, the SVT should never come back.

Antiarrhythmic drugs can also be used to attempt to prevent SVT, but since these drugs are often only partially effective, and many of them have the potential to cause significant side effects, most doctors are reluctant to prescribe chronic antiarrhythmic drug therapy to treat SVT - a benign arrhythmia that may occur only infrequently. In some patients, however, a single dose of an antiarrhythmic drug, taken at the onset of SVT, can help terminate the episode more quickly.

NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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