ischaemic heart disease: tutorial Flashcards
What is angina, and how is it different from a myocardial infarction?
Angina is chest pain or pressure caused by not enough blood flow to the heart muscle.
A myocardial infarction, on the other hand, is a heart attack, normally caused by the blockage of one or more coronary arteries.
The difference between them is that angina is caused by a partial blockage, while a myocardial infarction is caused by a complete occlusion.
What causes the pain in an MI
In a myocardial infarction, there is low perfusion, which means that the by-products of metabolism (such as CO2) aren’t washed away quickly enough, and they activate sensory neurones.
These neurones converge at the same area as the nerves affecting the chest and arm, meaning that those are affected as well. This is known as referred pain, and it why people often complain of such pain during a heart attack.
What causes the exercise intolerance?
In a normal heart, the resistance is low in the large coronary artery, and high in the arterioles. During exercise, metabolic vasodilation of the arterioles reduces the total resistance. This means that there is increased blood flow to meet the increased O2 demands.
In a heart with an atheroma, there is stenosis in the large coronary artery, increasing the resistance. This means that metabolic hyperaemia occurs at rest, so that the blood flow meets the O2 needs.
During exercise, arterioles will further dilate to reduce resistance, but the total resistance is still too high to dominate the stenosis.
This means that the O2 demand cannot be met, and angina develops.
What are the major risk factors for ischaemic heart disease?
- an increased systolic blood pressure (afterload)
- increased sympathetic nerve activity, which increases HR, contractility and vasoconstriction
What drugs can be prescribed to combat angina?
- NITRATES: vasodilators
- β-BLOCKERS: cardiac depressants
- CALCIUM-BLOCKERS: both vasodilators and cardiac depressants
