Bradycardia

An adult's resting heart rate is generally 60 to 100 beats per minute. Bradycardia means a heart rate slower than 60 beats per minute; American guidelines use a cutoff of 50 beats per minute for a slow heart rate that needs attention. A slow heart rate is not always a problem. Athletes, very fit people, and many people during sleep have a heart rate below 60 beats per minute without any symptoms.

Bradycardia becomes a problem when the heart can no longer pump enough blood or cannot speed up to meet the body's needs. As a result, the brain and muscles do not get enough blood flow. Symptoms can include fatigue, dizziness, shortness of breath during activity, difficulty concentrating, and even fainting.

Two Main Sources

Bradycardia comes from two parts of the heart's electrical system. First, the sinus node, the heart's natural pacemaker, produces signals too slowly or occasionally pauses. This group includes sinus bradycardia, covered on the Sinus Bradycardia page, as well as sinus node dysfunction that can alternate with a fast heart rate, covered on the Tachycardia-Bradycardia Syndrome page. Second, signals from the upper chambers (atria) are blocked along the conduction pathway to the lower chambers (ventricles). This condition is called atrioventricular block, covered on the Atrioventricular Block page.

Causes That Can Be Corrected

Before deciding on a device, the doctor looks for causes that can be corrected. Examples include medications that slow the heart rate, such as beta blockers, certain calcium channel blockers, digoxin, and antiarrhythmic drugs; an underactive thyroid gland; a potassium level that is too high; a heart attack; and pauses in breathing during sleep. Bradycardia from these causes often improves once the cause is treated. Do not stop any medication on your own; discuss it with your doctor.

When a Pacemaker Is Needed

A pacemaker is considered when a slow heart rate persists, causes symptoms, and its cause cannot be corrected. Before that, the doctor makes sure the symptoms really come from the slow heart rate and not from something else, such as low blood pressure. In high-grade atrioventricular block, a pacemaker is generally recommended even before symptoms appear, because of the risk of sudden fainting. The device is placed under the skin of the chest under local anesthesia, and most people who have one return to their usual activities.

The doctor first confirms whether the slow heart rate is actually causing symptoms, then looks for its source. You will be asked about your symptoms, exercise habits, sleep patterns, and all the medications you take, including beta-blocker eye drops for glaucoma.

An ECG shows the rate and type of bradycardia. Because a slow heart rate often comes and goes, a Holter monitor or long-term recorder is used to match symptoms with the rhythm recording. A treadmill test assesses whether the heart rate can rise during activity. Blood tests, especially thyroid function and potassium, look for causes that can be corrected. Echocardiography is done if structural heart disease is suspected. An electrophysiology study is rarely needed, only when the results of other tests are still unclear.

See a doctor if your pulse often feels slow and you tire easily, feel dizzy, get short of breath with light activity, or have trouble concentrating. A checkup is also needed if these symptoms appear after starting a new medication. A slow heart rate without symptoms in people who exercise regularly is generally not a cause for concern, but you can still discuss it with a doctor.

Go to the emergency room right away if:

• You faint or nearly faint
• A slow heart rate comes with chest pain or severe shortness of breath
• You develop sudden confusion, severe weakness, or pale, cold skin
• You have a pacemaker and again experience severe dizziness or fainting