Ischemic heart disease Intro

Question 1

Most common cause of myocardial ischemia

Answer 1

In more than 90% of cases, myocardial ischemia results from reduced blood flow due to obstructive atherosclerotic lesions in one or more of the epicardial coronary arteries; consequently, IHD is frequently referred to as coronary artery disease (CAD)

Question 2

Prevalence of ischemic heart disease

Answer 2

• Prevalence is increasing rapidly
• Estimated 200 million people live with IHD in the world
• 20.1 million persons have IHD in the USA

Question 3

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Answer 3

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Question 4

Populations affected by IHD

Answer 4

Population subgroups that appear to be particularly affected are men in South Asian countries, especially India and the Middle East

Question 5

Where does resistance to blood flow occur in the coronary arteries?

Answer 5

About 75% of the total coronary resistance to flow occurs across three sets of arteries:
1 large epicardial arteries (Resistance 1 = R1)
2 prearteriolar vessels (R2)
3 arteriolar and intramyocardial capillary vessels (R3).

Question 6

How much does each segment of the coronary artery contribute to vascular resistance?

Answer 6

In the absence of significant flow-limiting atherosclerotic obstructions, R1 is trivial; the major determinant of coronary resistance is found in R2 and R3

Question 7

What can the segments of coronary arteries be divided into?

Answer 7

• Macrocirculation (epicardial arteries)
• Microcirculation (small arteries, arterioles, and capillaries)

Question 8

Size of each segment of a coronary artery

Answer 8

• Epicardial arteries are more than 400 micrometers in diameter
• Small arteries are less than 400 micrometers in diameter
• Arterioles are less than 100 micrometers in diameter
• Capillaries are less than 10 micrometer in diameter

Question 9

Main stimulus for vasomotion in each segment of coronary artery

Answer 9

• Flow for epicardial arteries (autoregulayion)
• Pressure for small arteries (autoregulation)
• Metabolites for arterioles

Question 10

What is IHD also referred to as and why?

Answer 10

• Coronary artery disease (most common cause of IHD)
• Chronic coronary syndrome (CCS) if stable (referred to also as stable ischemic heart disease, SIHD)

Question 11

Main functions of the different segments of coronary arteries

Answer 11

• Transport for epicardial and small arteries
• Pressure regulation for small arteries and arterioles
  -Exchange for capilaries

Question 12

Path of coronary arteries

Answer 12

• Coronary arteries emerge immediately from the ascending aorta immediately distal to the aortic valve
• These initially course along the external surface of the heart (epicardial coronary arteries) and then penetrate the myocardium (intramural arteries), subsequently branching into arterioles, and forming a rich arborizing vascular network so that each myocyte contacts roughly three capillaries

Question 13

How long does diastole take up from the heart cycle?

Answer 13

At rest, diastole comprises approximately two-thirds of the cardiac cycle

Question 14

Tolerance of the heart to ischemia vs hypoxemia (+ e.g. of conditions that lead to hypoxemia)

Answer 14

• Ischemia not only limits tissue oxygenation (and thus ATP generation), but also reduces the availability of nutrients and the removal of metabolic wastes
• Thus, cardiac ischemia is generally less well tolerated than hypoxemia per se, such as may occur with severe anemia, cyanotic heart disease, or advanced lung disease

Question 15

How does IHD manifest as?

Answer 15

IHD can declare itself through one or more of the following clinical presentations:

*Myocardial infarction (MI), in which ischemia causes significant cardiac necrosis
*Angina pectoris (literally “chest pain”), in which ischemia is not severe enough to cause infarction, but the symptoms nevertheless portend infarction risk
*Chronic IHD with heart failure
*Sudden cardiac death (SCD)

Question 16

Causes of IHD

Answer 16

• Coronary atherosclerosis
• Coronary emboli
• Arterial thrombi
• Ostial narrowing due to aortitis
• Myocardial vessel inflammation
• Vascular spasm
• Microvascular angina

Question 17

What is microvascular angina?

Answer 17

Abnormal constriction or failure of normal dilation of the coronary resistance vessels

Question 18

Prevalence of myocardial infarction

Answer 18

~3–4% of the population has sustained a myocardial infarction

Question 19

IHD mortality

Answer 19

• Largest cause of mortality worldwide, accounting for over 12% of global deaths
• In the industrialized nations, this amounts to over 7.5 million casualties each year
• Predicted to also become number one cause of death in low income in countries
• Since peaking in the mid-1960s, the overall death rate from IHD has fallen in the United States by over 50%

Question 20

Why has mortality decreased in IHD?

Answer 20

• Prevention, achieved by modifying important risk factors, such as smoking, level of blood cholesterol, and hypertension. Additional risk reduction can occur through weight loss, exercise, and maintaining good glycemic control in diabetic patients
• Diagnostic and therapeutic advances, allowing earlier and more effective treatments.

Question 21

What are the major risk factors for atherosclerosis?

Answer 21

High levels of plasma low-density lipoprotein [LDL], cigarette smoking, hypertension, and diabetes mellitus

Question 22

Percentage of coronary artery blockage needed to cause symtpoms

Answer 22

• A fixed lesion obstructing greater than 70% of vascular cross-sectional area (so called “critical stenosis”) is typically cited as the threshold for symptomatic ischemia precipitated by exercise (characteristically manifesting as exertional angina)
• With this degree of obstruction, compensatory coronary arterial vasodilation is no longer sufficient to meet even moderate increases in myocardial demand.
• Obstruction of 90% of the cross-sectional area of the lumen generally leads to inadequate coronary blood flow, even at rest.

Question 23

What are therapeutic advances that have led to decreased mortality in IHD?

Answer 23

They include cholesterol- (and inflammation-) lowering drugs such as statins, thrombolysis for acute coronary occlusions, better medical management after MI, coronary angioplasty and stenting, coronary artery bypass graft (CABG) surgery, and improved therapies for heart failure and arrhythmias using left VADs (Ventricular assist devices), implantable defibrillators, and cardiac resynchronization approaches. Even a simple daily prophylactic aspirin can have therapeutic benefit

Question 24

How does the heart adapt to coronary artery narrowing?

Answer 24

• Slowly developing obstructions in chronic severe coronary narrowing and myocardial ischemia induce the formation of collateral circulation allowing alternate channels to perfuse at-risk myocardium
• When well developed, such vessels can by themselves provide sufficient blood flow to sustain the viability of the myocardium at rest but not during conditions of increased demand
• With progressive worsening of a stenosis in a proximal epicardial artery, the distal resistance vessels (when they function normally) dilate to reduce vascular resistance and maintain coronary blood flow.

Question 25

Location of athersclerotic plaques in coronary arteries

Answer 25

• Clinically significant plaques can be located anywhere along the course of the vessels, although they tend to predominate within the first several centimeters of the LAD and LCX
• Sites of increased turbulence in coronary flow, such as at branch points in the epicardial arteries, also have an increased change of developing atheresclerotic plaques
• Sometimes the major epicardial branches are also involved (i.e., LAD diagonal branches, LCX obtuse marginal branches, or posterior descending branch of the RCA), but atherosclerosis of the intramyocardial (penetrating) branches is rare thus most atherosclerotic stenoses can be accessed by coronary catheterization