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Ischemic Heart Disease
Chapter 6, pg.131-156
The Objectives for this assignment are combined with the ones from Chapter 5 on Atherosclerosis. The two subjects go hand-in-hand, but I’ll try not to overlap with Ashley too much. Here are the objectives restricted to my section:
Identify the major determinants of myocardial oxygen supply and demand; describe the rationale, pathophysiology and clinical utility of exercise stress testing
Describe the epidemiological characteristics of ischemic heart disease
Develop a rational plan for evaluation and management of a patient with chest pain
Intro and the basics:
Angina = condition where you have a mismatch between myocardial oxygen supply and demand.
The leading cause of angina is CORONARY ARTERY DISEASE
CAD = reduced myocardial oxygen supply due to atherosclerotic narrowing of the coronary vessels
Ischemic Heart Disease is the leading cause of death in the US
Objective # 1: The major determinants of myocardial oxygen supply and demand. Oxygen supply depends on
Oxygen carrying capacity of the blood
This term remains constant in the absence of anemia or lung disease
Rate of coronary blood flow.
This is the important one
Recall that coronary artery flow (Q) is directly proportional to perfusion pressure (P) and inversely related to coronary vascular resistance (R)
For the coronary arteries, most of the perfusion HAPPENS DURING DIASTOLE!!
This is because during contraction of the myocardium during systole, the coronary vessels are mashed closed when the muscle contracts (and I think Dr. Faber said that the blood can’t enter the coronary vessels from the aorta when the velocity of systole is so great. Did I make that up?)
So, blood enters the vessels during diastole when the myocardium is relaxed and the vessels aren’t compressed.
We can approximate the perfusion pressure of the coronaries by measuring the aortic diastolic pressure
Things that change the aortic diastolic pressure will thus change the perfusion pressure of the coronaries
EX: hypertension, aortic regurg will decrease aortic diastolic press.
The other key determinant in blood flow is coronary vascular resistance