Ask your doctor about any heart rhythm problems

Q. My father was diagnosed with SVT. Is that bad?

SVT stands for supraventricular tachycardia, an abnormally fast heart rhythm. It is not usually dangerous. SVT is one of many types of arrhythmia. An arrhythmia is a problem with the speed or rhythm of the heartbeat.

Most arrhythmias are harmless. Even serious arrhythmias can be treated successfully. Most people with arrhythmias are able to live healthy lives.

Millions of Americans have arrhythmias. They are very common in older adults. Arrhythmias are more common in people who have a disease or condition that weakens the heart.

Time for some anatomy. The heart is a fist-size muscle. It has four chambers - two atria on top and two ventricles below. There are four valves that open and shut with every heartbeat to control the circulation of the blood.

The heart has an internal electrical system that controls the speed and rhythm of the heartbeat.

With each heartbeat, an electrical signal spreads from the top of the heart to the bottom. As it travels, the electrical signal makes the heart contract and pump blood.

At rest, a healthy adult heart beats 60 to 100 times a minute. So, the heart of a person with a pulse of 80 beats a minute beats 115,200 times a day.

There are four main arrhythmia categories: premature beats, supraventricular arrhythmias, ventricular arrhythmias, and bradyarrhythmias.

Premature beats

Premature beats are the most common type of arrhythmia and can occur in the atria or the ventricles. They are usually harmless and need no treatment. A premature heartbeat is actually an extra beat between two normal heartbeats. This arrhythmia is commonly caused by too much caffeine, nicotine, stress, or exercise.

Supraventricular arrhythmias

Supraventricular arrhythmias are rapid heart rates known as tachycardias. They begin in the atria or between the atria and the ventricles. The types of these arrhythmias are atrial fibrillation, atrial flutter, supraventricular tachycardia, and Wolff-Parkinson-White Syndrome.

Atrial fibrillation, also called AF or AFib, is the most common type of dangerous arrhythmia. It's a very fast and irregular contraction of the atria.

Because the atria are beating rapidly and irregularly, blood does not flow through them as quickly.

This makes the blood more likely to clot. If a clot is pumped out of the heart, it can travel to the brain, causing a stroke. Infrequent and brief episodes of atrial fibrillation can be triggered by overindulgence in alcohol, caffeine and food.

Atrial flutter is a fast and regular rhythm. Atrial flutter is much less common than atrial fibrillation, but has similar symptoms and complications.

Supraventricular tachycardia, as described earlier, is an abnormally fast heart rhythm. This type of arrhythmia tends to occur in young people. It can happen during vigorous exercise.

Wolff-Parkinson-White syndrome is a condition in which the heart's electrical signals travel along an extra pathway from the atria to the ventricles, disrupting the heart's timing. WPW can make the ventricles beat very fast, and it can be life-threatening.

Ventricular arrhythmias

These arrhythmias begin in the ventricles. They include ventricular tachycardia and ventricular fibrillation. They usually are dangerous and need emergency treatment.

Ventricular tachycardia is a fast, regular beating of the ventricles. Ventricular tachycardia episodes that last for more than just a few seconds can be dangerous. This condition can evolve into more dangerous arrhythmias.

Ventricular fibrillation (V-fib) happens when disorganized electrical signals make the ventricles quiver instead of pump normally. If the ventricles don't pump blood to the body, it will die within minutes. V-fib requires defibrillation, an electric shock to the heart.

Bradyarrhythmias

Bradyarrhythmias are arrhythmias in which the heart rate is slower than normal. If the heart rate is too slow, not enough blood reaches the brain, and insufficient blood can make you pass out. In adults, a heart rate slower than 60 beats per minute is considered a bradyarrhythmia.

Bradyarrhythmias can be caused by heart attack, an underactive thyroid gland, aging, a chemical imbalance, or some medicines.