b. When the heart is stressed, it must rely on increased coronary blood flow to
meet the increased oxygen demand of the cardiac tissue. Coronary blood flow is
determined by the amount of pressure in the aorta and the amount of resistance in the
coronary arteries. If atherosclerosis is present in the coronary vascular system,
coronary blood flow is decreased because of the increased resistance in the coronary
arteries.
c. The pain of angina pectoris occurs when the heart is stressed or worked to a
point where the oxygen demand is greater than the amount of oxygen that can be
delivered. This usually occurs with some type of exertion, such as mowing the lawn,
climbing stairs, or doing heavy housework. In the affected patient, the onset of pain will
occur with exertion, and relief will normally occur with rest. Rest will decrease the
workload on the heart, thereby decreasing the heart's oxygen demand and relieving the
pain.
d. Unstable angina pectoris is a term used to describe the exacerbation of the
symptoms of angina pectoris. This syndrome is characterized by increased severity of
symptoms, increased ease in provoking attacks of angina, and less predictability in
controlling angina attacks. Symptoms may be severe enough to mimic an acute
myocardial infarction. Crescendo angina and acute coronary insufficiency are also
terms used to describe unstable angina.
e. In either case, medical management is the same. The patient is educated
about the nature of the disease so that it may be controlled with diet, medication,
exercise, and risk factor modification. When the condition advances to the stage where
it can no longer be controlled in this manner, surgical intervention may be indicated.
Two surgical possibilities include the coronary artery bypass graft (CABG) and
transluminal coronary angioplasty (balloon compression).
1-26. ACUTE MYOCARDIAL INFARCTION
a. Acute myocardial infarction (AMI) results from an imbalance between oxygen
demand and oxygen supply to the myocardium. In 90 percent of the cases of AMI, this
imbalance is preceded by atherosclerosis and decreased blood flow in the coronary
arteries. The inadequate blood flow results in decreased oxygen delivery to the heart
muscle, which causes ischemia, injury, and death of a portion of the myocardium
(infarction).
b. Myocardial infarctions are described as being anterior, inferior, or posterior,
depending upon the location of the infarcted area of the heart muscle. Infarcts can be
further classified as being transmural or non-transmural. A transmural infarct (Non Q-
Wave MI) is one that involves damage to the full thickness of the myocardium. A
nontransmural MI involves only a partial thickness of the muscle.
MD0917
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