Ischemic Heart Disease

Question 1

What causes cardiac ischemia?

Answer 1

Cardiac ischemia results from an imbalance between myocardial oxygen supply and demand.

Question 2

What are the determinants of myocardial oxygen supply?

Answer 2

• the oxygen content of the blood
• coronary blood flow

Question 3

What are the key regulators of myocardial oxygen demand?

Answer 3

• the heart rate
• contractility
• myocardial wall stress

Question 4

In the presence of CAD, what two factors compromise myocardial oxygen supply?

Answer 4

• atherosclerotic plaques that narrow the vascular lumen
• endothelial cell dysfunction that causes inappropriate vasoconstriction of coronary resistance vessels

Question 5

What is the main cause of ischemic heart disease?

Answer 5

Approximately 90%
caused by atherosclerosis
of the coronary arteries
(coronary artery disease)

Question 6

What is normal aortic diastolic pressure?

Answer 6

60-80 mmHg

Question 7

What part of the heart is most vulnerable to ischemic damage?

Answer 7

Subendocardium

Question 8

Angina may be accompanied by signs and symptoms of the following:

Answer 8

• adrenergic stimulation (sympathetic nervous system)
• pulmonary congestion
• transient left ventricular systolic and diastolic dysfunction

Question 9

What is the standard pharmacological therapy for chronic angina to prevent ischemia and relieve symptoms?

Answer 9

• beta blockers
• nitrates
• calcium channel antagonists
  (alone or in combo)
• aspirin
• statins
• ACE inhibitors

Question 10

Describe ventricular wall stress.

Answer 10

Refers to the force pulling myocardial fibers apart + energy
used to oppose that force

Wall stress is related to:
* Intraventricular pressure
* Ventricular radius
* Ventricular wall thickness

Wall stress is proportional to systolic ventricular pressure

Question 11

Describe the relationships between increased and decreased heart rate.

Answer 11

↑HR causes ↑contraction /minute, ↑ATP consumption per
minute and ↑myocardial O² consumption

↓HR causes ↓contraction /minute, ↓ATP consumption per
minute and ↓myocardial O² consumption

Question 12

What factors influence contractility that influence myocardial oxygen demand?

Answer 12

• Circulating catecholamines or positive inotropic drugs
  increases contractility and myocardial O² consumption
• β-adrenergic-blocking drugs (negative inotropes)
  decreases contractility and myocardial O² consumption

Question 13

Reduction of blood flow is a combination of these two factors.

Answer 13

• fixed vessel narrowing
• abnormal vascular tone

Question 14

What happens when vessel stenosis narrows diameter by >70%?

Answer 14

A decrease in maximal blood
flow even with full dilation of distal resistance vessels.

Question 15

What happens when vessel stenosis narrows diameter by >90%?

Answer 15

Even maximal dilation of distal resistance vessels is inadequate to meet basal requirements. This results in myocardial ischemia even at rest.

Question 16

Endothelial cell dysfunction contributes to pathophysiology of ischemia in 2 ways:

Answer 16

• Inappropriate vasoconstriction of coronaries
• Loss of normal antithrombotic properties

Question 17

What are some causes of decreased myocardial oxygen supply?

Answer 17

• Decreased perfusion due to hypotension, hypovolemia,
  hemorrhage
• Decreased blood O2 content due to anemia or impaired blood oxygenation by the lungs

Question 18

What are some causes of increased myocardial oxygen demand?

Answer 18

• Rapid tachycardias
• Profound acute hypertension
• Severe aortic stenosis

Question 19

What are some consequences of ischemia?

Answer 19

• pulmonary congestion
  and dyspnea
• Metabolic products such as lactate, serotonin, and
  adenosine accumulate locally
• angina
• dangerous arrhythmias
• stunned myocardium
• hibernating myocardium

Question 20

What are some of the diagnostic tests of myocardial ischemia?

Answer 20

• ECG
• Exercise stress testing
• Nuclear stress testing
• Pharmaceutical stress testing