Heart block
Heart block occurs when impluse formation is impaired or conduction is prevented,and the delay between atrial and ventricular contraction is increased.the severity depends on the extent of loss of stimulation of the AV node.
In complete heart block, ventricular contraction is entrirely independent of impluses initiated by the SA node.impluses generated by the AV node result in slow,regular ventricular contractions and a heart rate of about 30 to 40 beats per minute.in this state the heart is enable to respond quickly to a sudden increase in demand by,e.g., muscular exercise. The most common causes are:
1)acute ischaemic heart disease
2)myocardial fibrosis following repeated infarctions or myocarditis
3)drugs used to treat heart disease,e.g.digitalis,propranolol.
When heart block develops gradually there is some degree of adjustment in the body to reduced cardiac output but,if progressive,it eventually leads to death from cardiac failure and cerebral anoxia.
May 2nd, 2008 at 11:17 pm
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