Heart Block is a type of bradycardia (too-slow heartbeat) that also is called atrioventricular, or AV block. In this condition, the electrical signals that stimulate heart muscle contractions are partially or totally blocked between the upper chambers (atria) and the lower chambers (ventricles).
Sudden cardiac arrest (SCA) occurs when the heart stops beating, abruptly and without warning. If the heartbeat is not restored with an electrical shock immediately, death follows within minutes.
Death from cardiac arrest is called sudden cardiac death (SCD). It accounts for about half of all heart disease deaths in the United States. Learn more about who is at risk for SCA.
The atrioventricular (AV node) receives signals from the sinoatrial (SA) node, the heart's master pacemaker, and transmits them to the lower chambers (ventricles) of the heart.
The ventricles are the major pumping chambers of the heart. The electrical signal transmitted from the SA and AV nodes trigger the muscle contractions that pump blood out of the heart and into the lungs and body.
What are the types of heart block?
First-degree heart block (also called first-degree AV block). The electrical impulses are slowed as they pass through the conduction system, but all of them successfully reach the ventricles. First-degree heart block rarely causes any symptoms or problems, and well-trained athletes may have this. Medications can contribute to the condition. No treatment is generally necessary for first degree heart block.
A structure called the bundle of His emerges from the AV node and divides into thin, wire-like structures called bundle branches that extend into the right and the left ventricles. The electrical signal travels down the bundle branches to thin fibers that distribute the electrical impulse to the muscles of the ventricles, the major pumping chambers of the heart.
Bundle Branch Block often produces no symptoms, although some people may either faint (syncope) or feel as if they're going to faint (presyncope). If both bundles are diseased, heart block may result producing syncope (fainting) or preseyncope (feeling like fainting). When this happens, the heartbeat may be so slow that an artificial pacemaker is implanted, even if the heart is otherwise healthy. Treatment may also be necessary if bundle branch block is caused by an underlying heart condition, such as damage to the heart muscle from a heart attack (myocardial infarction). Depending on where the damage is located, a person may be diagnosed with one of several specific types of bundle branch block, including:
Left bundle branch block (LBBB) is when there is a defect in the left bundle branches that convey electrical signals to the ventricles; if the defect is in the right bundle branch, it is called right bundle branch block (RBBB).
Trifascicular block occurs when an individual is diagnosed with a form of bifascicular block as well as a first-degree heart block.
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