An arrhythmia occurs when the heart's regular rhythm changes, such as speeding up or slowing down, or when it beats irregularly.

In North America, about 5 million people get arrhythmias, most over the age of 50. Some also have heart disease, but many don't. In the vast majority of cases, the arrhythmia by itself isn't life-threatening, but it may predispose someone to a number of problems, such as a stroke. There are many different types of arrhythmias and their significance and consequences are varied.

The normal beating of the heart is controlled by electrical signals sent from a particular segment of heart muscle tissue called the sinus node. This natural pacemaker is located near the top of the right atrium. The heart is divided into four chambers: two atria on top, and two ventricles underneath. The job of the atria is to fill the ventricles with blood, which then do the heavy work of pumping it through the rest of the body.

In a normal heartbeat, an electrical pulse travels down the muscle tissue, activating the ventricles a split second after the atria. In arrhythmias, there's a problem with this signal. There are many different kinds of arrhythmias, but those that affect the ventricles are generally more serious than arrhythmias of the atria.

Arrhythmias are can be caused by either slow heartbeats (bradycardia) or fast heartbeats (tachycardia). A slow heart rate may occur due to:

• Sick sinus syndrome: This occurs when the heart’s natural pacemaker breaks down, causing slower transmission of the electrical signals that contract the heart. It occurs more frequently in the elderly and may worsen with certain medications (e.g., beta blockers) that also slow down the heart rate.
• Heart block: This occurs when the electrical signal sent from the upper heart chambers (atria) to the lower heart chambers (ventricles) is interrupted. Without this signal transmission, the heart cannot contract efficiently to pump blood out into the body.

A fast heart rate can be the result of:

• atrial fibrillation (AF): This involves disordered signals that are fired off in rapid succession, causing fibrillation, which is an uncoordinated quivering of the muscle wall of the atria. This has often been described as looking like a "bag of worms." The atria stop pumping blood effectively, yet enough blood still reaches the ventricles to allow the heart to function. AF is potentially dangerous, however, because blood can pool in the atrium and lead to clot formation. If one of these clots travels to the brain, it causes a stroke. AF is the most common form of harmful arrhythmia, affecting almost 1% of the population. It is more common in seniors, affecting about 5% of people over age 69. One study showed that 1 in 4 people over the age of 40 will develop AF.
• ventricular fibrillation (V-fib or VF): This is the most dangerous form of arrhythmia. The ventricles twitch but don't pump blood. If the twitching does not stop on its own or by a shock from a defibrillator, it is always fatal.

When the heart beats faster than normal, it's called tachycardia. Symptoms include chest discomfort, palpitations, lightheadedness, dizziness, and sometimes fainting. When it beats slower than normal, it's called bradycardia. Bradycardia can cause fatigue, lightheadedness, dizziness, and fainting as it tends to produce low blood pressure.

Everyone knows what it feels like to experience an occasional flutter of the heart, and usually it doesn't mean anything. But if you get chest pains, feel faint, or you notice your pulse to be irregular or either very rapid or very slow over a prolonged period, it's time to see a doctor.

The stethoscope is still a valuable instrument when it comes to detecting arrhythmias, but there are modern tests that can pinpoint the problem.

The electrocardiogram (ECG) prints a graph of the heart's electrical activity using small electrodes taped to the chest. The pattern on these graphs reveals the type of arrhythmia. Since the arrhythmia might not occur at the hospital, there are portable ECGs that you can bring home. Some are constantly turned on over a specified period of time (called a Holter monitor), while others are turned on when you feel an arrhythmia (called an event monitor or loop recorder). Some of these devices can download the heart signal data over a phone line or a cell phone. Certain arrhythmias may be associated with exercise, therefore you may be asked to walk on a treadmill or ride a stationary bicycle while hooked up to an ECG machine.

Electrophysiologic study (EPS) is a more elaborate test. Thin tubes are inserted into a blood vessel in the leg and guided up to the heart. They hold electrodes that can find the muscle tissue that may be causing abnormal electrical activity.

In some cases, arrhythmias are due to bad habits like drinking too much alcohol. Breaking the habit can cure the problem. Reducing stress, avoiding caffeine, improving your diet, and increasing the amount of exercise you do in a week can also reduce the frequency of experiencing arrhythmias. You should talk to your doctor first before beginning such changes. In other people, the arrhythmias are a symptom of heart disease, and they won't go away unless this underlying problem is addressed. Fortunately, many people can benefit from modern medical interventions, especially in the area of surgery and the insertion of special electrical devices.

There are several medications that can slow down a rapid heartbeat (known as "rate control"). Beta-blockers (e.g., atenolol, metoprolol)* are medications that are very useful for rate control in people with a variety of heart conditions. Calcium-channel blockers (e.g., diltiazem, verapamil) may also be used for rate control. Often, these medications can be used for more than one purpose (i.e., heart rate control, high blood pressure, heart protection after a heart attack). Another medication, digoxin, is derived from a substance called digitalis that has been used for arrhythmias for over 200 years.

Other medications called antiarrhythmics can convert an abnormal rhythm back to normal, and prevent it from recurring (known as "rhythm control"). Examples of antiarrhythmics include amiodarone, propafenone, and sotalol. Patients with atrial fibrillation (AF) are usually given the anticoagulant warfarin, which thins the blood to keep blood clots from forming and causing strokes. Recent research has shown that rate control and adequate anticoagulation are very important (perhaps even more important than rhythm control) for people with certain kinds of arrhythmias (e.g., AF).

In some cases, AF is converted back to a normal rhythm by a treatment called cardioversion, in which a doctor gives the patient a sedative followed by a small electrical shock that "resets" the natural pacemaker in the heart.

Many arrhythmias can be cured outright with radiofrequency ablation. The same tubes used in EPS (see "Making the Diagnosis") are inserted into the heart to send radio waves directly onto electrical pathways carrying inappropriate signals. These waves ablate (destroy) the abnormal tissue, preventing it from triggering an abnormal heart rhythm.

Artificial pacemakers can take over the job of generating the electrical signals. Once limited to treating slow heart rates, the latest pacemakers can control fast heart rates, too. They can run up to 15 years on one battery. Some save power by switching off when the heartbeat is normal. Most units are placed under the skin, requiring only minor surgery.

Defibrillators are devices that restart arrested hearts with jolts of electricity to the chest. Defibrillators are effective at stopping ventricular fibrillation, but since ventricular fibrillation can be fatal in less than 4 minutes, they must be used early. Most defibrillators are external devices, but now there are automatic implantable cardiovertors/defibrillators (AICD). These devices can be as small as pacemakers. They can detect a dangerous fibrillation and jolt the heart back to normal before any harm is done. As one doctor puts it, "it's like having an emergency room implanted in your chest."

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