About Heart Arrhythmias

The normal heart

Your heart normally beats about 100,000 times a day, which translates to 60-100 beats per minute. It does this in an orderly fashion, controlled by a steady stream of electrical impulses.

The heart consists of two upper chambers, called the atria, and two lower chambers, called the ventricles. Electrical impulses that coordinate the heart’s contractions originate at the sinoatrial node — also called the sinus node or SA node.

The SA node is a bundle of highly specialized cells in the right atrium. The signal passes through the right and left atria, telling them to contract. When the atria contract, oxygen-rich blood is pushed into the ventricles. Then the atrioventricular node, or AV node, receives the signal and passes it into the ventricles, telling them to contract. When the ventricles contract, blood is pumped out of the heart into the body.

Abnormal heart rhythm

Sometimes, however, the flow of electrical impulses changes. The sinus node may send out signals too quickly, or it may send out extra signals. In other cases, the signals bounce around inside one of the heart’s chambers instead of moving on in a regular pattern.

The result is a fast or irregular heartbeat. These abnormal rhythms are called arrhythmias (pronounced: uh - rith - mee - uhs). When the heart beats erratically, it does not pump blood as efficiently as it should, shortchanging the delivery of oxygen throughout the body.

When this abnormal rhythm results in a heart rate that is faster than normal, it is called tachycardia. Tachycardias are given different names depending on where the abnormal signal originated. For example:

When the SA node in the right atrium misfires, the resulting abnormal rhythms are called atrial arrhythmias or atrial tachycardias.
Abnormal rhythms that arise from the AV node are called ventricular tachycardias.
Sometimes the abnormal signals bounce around inside one of the heart’s chambers; this is called a re-entrant tachycardia.
Arrhythmias that originate at the SA node or in the atria are also sometimes called supraventricular (literally, “above the ventricles”) tachycardias; they may affect both the atria and the ventricles.

We do not yet fully understand what causes the heart’s electrical system to misfire. Tachycardias occur often among people who have had previous heart trouble, particularly those whose heart has been damaged by a heart attack or surgery. They are also more common as a person ages, so people over the age of 65 are at greater risk.

Most arrhythmias are harmless and occur in people with healthy hearts. Some are a natural response, such as the heart beating faster in order to meet your body’s demand for increased oxygen when you exercise. But sometimes they are dangerous — and can even be fatal.

Symptoms

Some patients with tachycardias have no symptoms, while others are severely impaired. Symptoms cover a wide range, from feeling lightheaded to sudden cardiac death. Symptoms are caused by the lack of steady blood flow to the body and can include:

Palpitations
Rapid heart rate
Shortness of breath
Chest pain
Dizziness
Lightheadedness
Fainting

Diagnosis

In order to diagnose an arrhythmia, doctors order specific tests, depending on the type of arrhythmia that is suspected. In addition to blood tests, your doctor may order:

Echocardiogram
24-hour electrocardiogram, or ECG (in which you wear a vest-like device called a Holter monitor during normal activity)
Electrophysiology study (used to locate the origin of the rhythm disorder and determine the best treatment)

Treatment

Some tachycardias are very brief or mild and do not pose a serious threat. Others require long-term treatment, and some are life-threatening. The treatment depends on the type of disorder — its frequency, duration, symptoms, and associated risks. Treatment decisions should also take into account any underlying heart conditions.

In very severe and life-threatening arrhythmias, emergency treatment to restore normal rhythm immediately may be done via electrical cardioversion from a defibrillator or through the use of intravenous drugs.

For less-severe conditions whose symptoms are bothersome, long-term treatment is needed. It usually involves the use of medications to stabilize the heartbeat. These may include:

Antiarrhythmic agents to maintain the heart’s normal rhythm
Beta-blockers to slow the heart rate
Calcium channel blockers to slow the heart rate and suppress tachycardias

Certain types of arrhythmias, such as atrial fibrillation, come with a high risk of stroke, and patients should also receive blood thinners.

Specialized treatments have recently been developed to restore the heart’s normal rhythm and reduce the risks that accompany heart rhythm disorders. These include:

Implantable cardioverter-defibrillator (ICD): This is a device which is inserted into the patient’s chest, like a pacemaker. ICDs are the treatment of choice for ventricular tachycardia; when an episode begins, the device delivers a shock to end the tachycardia. This prevents the heart from going into ventricular fibrillation, which is frequently fatal.
Catheter ablation: This specialized procedure is the treatment of choice for most supraventricular tachycardias, including atrial flutter and Wolff-Parkinson-White syndrome. Also called radiofrequency ablation, it is increasingly being used today for ventricular tachycardia, and is under investigational studies for treatment of atrial fibrillation as well. This treatment involves the placement of tiny wires called catheters inside the heart, where they deliver high-energy waves that destroy the areas causing the abnormal rhythm, preventing further triggering of tachycardia.

According to the National Institutes of Health, “Most supraventricular arrhythmias can be treated and cured with radiofrequency ablation, eliminating the need for lifelong drug therapy.”

For more information:

Heart Rhythm Society
www.hrspatients.org »

American Heart Association
www.americanheart.org »
From the home page, click on “Diseases and Conditions”, then on “Arrhythmias”.

National Institutes of Health
www.nlm.nih.gov/medlineplus/encyclopedia.html »
Select the entries for arrhythmias, atrial fibrillation/flutter, ventricular tachycardia, Wolff-Parkinson-White syndrome, supraventricular tachycardia, and EP study.