Wednesday, June 8, 2011

Second-Degree Heart Block - Heart Block

Overview, Causes, & Risk Factors

Heart block is a disruption in the relay of electrical signals that control activity of the heart muscle.
What is going on in the body?
The heart beats by using electric impulses. These impulses follow a specific route through the heart. These routes or pathways are sometimes grouped together into specialized areas called nodes and bundles.
Bundles send out little fibers that go into the muscle of the heart. The nodes, bundles, and fibers are responsible for the unified beating of the heart and the rate at which it beats. A defect along any of these pathways can cause a heart block. This does not mean the blood flow or blood vessels are blocked.
There are many kinds of heart block. Each type depends on where the damage has occurred in the electrical pathway.
  • First-degree heart block. This type occurs when the electrical impulse passes through the heart slower than normal, but heartbeat and rhythm are still within a healthy range. This type of block does not mean there is anything really wrong with the heart.

  • Second-degree heart block. This occurs when some of the electrical signals from the upper chamber of the heart, called the atrium, don't reach the lower chamber of the heart, called the ventricle. This results in what are called "dropped beats."

  • Complete heart block.This is the worst form of heart block. In this condition, no electrical impulses pass from the upper to the lower parts of the heart, so the lower part starts beating on its own, but at a much slower rate than is healthy. When this occurs, the lower part of the heart may not beat fast enough or regularly enough to keep blood flowing to the vital organs.

  • What are the causes and risks of the disease?
    Many times, heart block is a symptom that the person has another type of heart disease. Heart blocks are common in people who have:
  • history of heart attacks

  • coronary artery disease

  • infectious diseases of the heart, such as endocarditis

  • hereditary defect of the heart, called congenital heart block

  • Certain medicines can also cause heart block if the levels in the body build up too much. Some examples include:
  • beta blockers, such as propanolol or pindolol

  • calcium channel blockers, such as verapamil or diltiazem

  • digitalis glycosides, such as digoxin

  • Highly-trained athletes may also have the less severe forms of heart block, but will most likely have no symptoms other than a slow heartbeat.
    A block that has existed for a long time may pose no problem. A block that appears suddenly may be due to a new heart problem or the worsening of an old one. A change in the heart block can alert the doctor to a change in the status of the heart.

    Symptoms & Signs

    What are the signs and symptoms of the disease?
    Symptoms depend on how severe the heart block is and in what part of the heart it occurs. Often, heart block causes no symptoms. If the heart block is severe enough, the heart rate will slow, and symptoms of low blood pressure or stroke will appear. The person may feel dizzy, weak, confused, or may have less tolerance for exercise. At times, some people may even pass out.

    Diagnosis & Tests

    How is the disease diagnosed?
    An electrocardiogram, which is a test also called ECG or EKG, can diagnose the disorder. Heart blocks often have a certain pattern that the ECG machine traces on special paper. In some cases, special tests using probes placed into the heart can measure the flow and direction of electricity.

    Prevention & Expectations

    What can be done to prevent the disease?
    Treatment of an existing heart problem can make heart blocks less likely to develop or worsen. Avoiding medicines that cause heart block may also help in some people. There is no way to prevent a heart block from occurring in a healthy person.
    What are the long-term effects of the disease?
    The long-term effects of heart block depend on the underlying heart disease. Heart block is a sign of the disease process. If the underlying disease causes a fixed slow heart rate, less than 45 beats/minute, then a pacemaker will be needed. If the underlying disease does not get worse, then the heart block is not a concern. If a new heart block appears suddenly where there was none before, it can result in a heart attack.
    In summary, the worse the underlying disease the worse the block. The worse the block, the slower the heart rate. The slower the rate, the worse the symptoms. Common symptoms are:
  • fainting

  • stroke

  • sudden death

  • What are the risks to others?
    Heart block causes no risk to others.

    Treatment & Monitoring

    What are the treatments for the disease?
    Many times heart blocks are not treated at all. Treatment of other heart problems reduces the risk of the block getting worse.
    In some cases, the block becomes so severe that heart can no longer beat fast enough to keep the body healthy. When this occurs, an electrical device called a pacemaker can be used to help the heart beat at a healthy rate. Medicines can also be used to help restore the heart rate. Or, the doctor may substitute a different medicine when the block is the result of a side effect from a certain type of medicine.
    What are the side effects of the treatments?
    Pacemakers use batteries to work. These batteries can last for years, but will need to be replaced at some point. The pacemaker itself may also need replacing after years of use. The side effects of medicines used to treat heart disease vary, depending on the medicine.
    What happens after treatment for the disease?
    Once a pacemaker is implanted, the doctor will monitor the person's heart rate with each office visit. Medicine for existing heart disease may also need to be adjusted from time to time. With the correct treatment, most people are able to continue with their regular activities.
    How is the disease monitored?
    Regular visits to the doctor and repeat ECG testing, sometimes by telephone, helps pick up any changes in the heart's status. Any new or worsening symptoms should be reported to the doctor.


    Author:Eric Berlin, MD
    Date Written:
    Editor:Crist, Gayle P., MS, BA
    Edit Date:09/17/02
    Reviewer:Kathleen A. MacNaughton, RN, BSN
    Date Reviewed:09/17/02

    Merck Manual, 1999
    Harrison's : Principles of Internal Medicine,1991
    Current Medical Diagnosis and Treatment, 1996