HEART BLOCK, SECOND-DEGREE

Heart block refers to a delay of conduction of electrical signals from the atrium through the atrioventricular node (part of the electrical wiring of the heart). This node carries the electric signals from the atria that tell the ventricles to contract. The block can affect different parts of the conduction system of the heart. It is generically referred to as heart block, and there are many different types of blocks of electrical signals in the heart. Second-degree heart block affects the node (type I block) or conduction below the node (type II block). The atria contract normally, but because they do not receive the proper signal, the ventricles may not contract as often as they are supposed to.

Symptoms of heart block relate to insufficient pumping of blood from the heart. Heart block may produce no symptoms. Often it can cause extreme fatigue, lightheadedness, or syncope (fainting). Severe heart block can cause angina (chest pain) or stroke (not enough blood flow to the brain).

Heart block is relatively common. About one half of persons with heart block have no known cause. Most of the others have some form of heart disease. They may have had damage to the heart from a heart attack (myocardial infarction) or myocarditis (inflammation of the heart muscle). Heart block may come from overdosing of digitalis medications (digoxin). It may also be caused by some a congenital heart abnormality (one that is present at birth). Heart block is detected with an electrocardiogram (ECG). Usually the patient has normal impulses from the atrium, but there is evidence that some of the impulses do not reach the ventricles.

A patient with type I second-degree heart block may have no symptoms. Type II block is usually the result of heart disease. Patients with type II block are at risk for complete heart block, cardiomyopathy (disease of the heart muscle), or death from asystole (the heart not beating). Medications that cause the condition have to be stopped or changed.

If you have type I block and have no symptoms and no heart disease, no treatment is required. Patients with either type of heart block or those who have symptoms because the ventricle is not beating fast enough to meet blood demands may need a pacemaker (Fig 1). A pacemaker is an electrical device with a wire to the heart muscle that signals the ventricles to contract regularly (fixed-rate pacers) or to beat faster in response to increased activity (demand pacers). The pacemaker may be external with the wire entering through a vein, or it may be implanted in the patient with a minor operation. Older pacemakers were susceptible to damage from microwaves and strong electronic equipment. New pacemakers are safer and more reliable. You must still exercise caution around strong magnetic or ultrasonic forces such as those used in some physical therapy settings or in airport security screens. If you have a pacemaker, you will be given instructions by the cardiologist regarding maintenance and care of the pacemaker.

• Make your diet one for a healthy heart, which means make it low in fat and cholesterol. Lose weight and stop smoking.
• Continue other medical treatments as directed.

• Do not exercise until you have clearance from your physician.

• If you have worsening dizziness, fainting, chest pain, or shortness of breath.

Contact the American Heart Association at 1-800-242-8721 and ask for the literature department.




Cardiac pacemaker. (From LaFleur-Brooks ML: Exploring Medical Language–A Student Directed Approach, ed 3, St. Louis, Mosby—Year Book, 1993. Used by permission.)

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