In the normal heart, the contraction of the heart is regulated by a series of fibers that begin in the upper chamber, or atrium, and pass to the lower chambers, or ventricles. These impulses regulate the rate of contraction and coordinate the sequence of contraction so as to optimize cardiac pump function. Disruption in transmission of these electrical signals leads to loss of synchronization between the atria and the ventricles. The heart block can be partial or complete. Heart block is classified be degrees. When there are no clinical symptoms, only changes on the EKG, it is considered first degree heart block. Second degree heart block occurs when some of the electrical impulse sent from the atria are not conducted to the ventricles. This results in an irregular heart beat. In third degree heart block, none of the pulses of the atria are conducted to the ventricles. The ventricles must be on their own, usually at a rate that is too slow to maintain normal function.
Causes of Heart Block
Heart block can be caused by coronary artery disease, a form of atherosclerosis, congenital heart abnormalities, excessive digitalis, calcium channel blockers and previous heart attack. Some infections, such as Lyme disease and infectious mononucleosis can produce various degrees of heart block.
Signs and Symptoms of Heart Block
First degree heart block does not produce any symptoms. An irregular or slow heart beat, or palpitations, are felt with second degree heart block. There can be shortness of breath and fatigue or exhaustion. If the rate is slow enough, as might occur with third degree heart block, there may be fainting or loss of consciousness. Dizziness, confusion or seizures can occur.
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Medical Content Last Updated on 07/12/2008
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