Heart Block

Heart block, also known as atrioventricular block, is a condition in
which conduction of the cardiac action potential from the atrium to the
ventricle is impaired.  

There are three degrees of heart block.  First degree AV block is when
the P-R interval is longer than 0.2 seconds, and can be caused when the
atrial depolarization rate is too fast.  The autonomic nervous system will
react by slowing the P-R interval time to allow the ventricles adequate
filling time.  The effect lasts until the atrial depolarization rate slows
down.  

The other degrees of heart block are caused by a strong autonomic response
and are more serious than 1st degree AV block.  Second degree heart block
occurs when some, but not all of the impulses from the atrium are not
conducted to the ventricle.  This is a result of the ANS trying to
protect the ventricles from contracting too much and becoming
damaged.  Third degree, or complete heart block, happens when no impulses
at all are conducted.  This condition often requires the use of a
pacemaker to correct. 

Sample Problem:

Multiple Choice:
There are three degrees of heart block.  List in order of severity:
A. 1st degree AV block
B. 2nd degree AV block
C. 3rd degree AV block

Answer:

C, B, A

For more information on this topic, please refer to Berne & Levy , p. 33-35, 213

Also, check out the following links that may be helpful:

• The Merck Manual: Cardiovascular disorders
• ECG Library Homepage
• Amy edwards

No!
Please don't make me go to any of those pages!
I want to go somewhere completely different!

This page was written by Karolynn Bayaca
Karol's world , a student in this course.

BME 403 Pages maintained by the T.A., Douglas Miles.