CVS Angina and acute coronary syndrome Flashcards
How many times more supply does coronary circulation require than unstimulated skeletal muscle does?
Needs a high supply of O2 – 20x of unstimulated skeletal muscle
What do cardiac muscles have a high density of and how does this impact diffusion?
-Cardiac muscle has high density of fibres and capillaries
-Shorter passive diffusion distances
What does a high capillary density and a large surface area do together in cardiac muscle?
-High capillary density
-Large surface area for O2 transfer
-Together these reduce diffusion
distance of O2 to myocyte
What times the blood flow is present in coronary circulation during normal activity?
- 10x the flow per weight of rest of body
How much O2 extraction is there in comparison to the average body in coronary circulation?
High O2 extraction (75%) - average body is 25%
What happens to coronary circulation during increased demand and how?
-Coronary blood increases in proportion to demands
-Production of vasodilator molecules from active cardiac muscle
e.g. adenosine, K+, acidosis
Produce local vasodilation
-Circulating adrenaline dilates coronary vessels due to beta-2 adrenoceptors on coronary artery vascular smooth muscle cells
When does coronary blood flow occur and when is it obstructed?
-Systole obstructs coronary blood flow
-Coronary blood flow only occurs during diastole
What are sudden obstructions that can occur in the heart?
Acute thrombosis, Acute Coronary Syndrome (ACS) including myocardial infarction
What are slow obstructions that can occur in the heart?
Atheroma (sub-endothelium lipid plaques)
chronic narrowing of lumen, produces angina
Why is coronary blood flow restricted during diastole?
Pressure in ventricles is = or > aorta
-Poor coronary perfusion
What are mechanical factors reducing coronary flow?
(1) Shortening diastole, e.g., high heart rate
(2) Increased ventricular end-diastolic pressure, e.g., volume-overload heart failure
(3) Reduced diastolic arterial pressure, e.g., hypotension
What type of arteries are the coronary artery?
Human coronary arteries are functional end-arteries
What happens when there is a total occlusion of left anterior descending coronary artery?
-Leads to ischemic area resulting in myocardial infarction
Steps involved from ischaemic tissue till cell death?
ischemic tissue, acidosis, pain (stimulation of C-fibres) –> impaired contractility –> sympathetic activation –> arrhythmias –> cell death (necrosis)
What does it mean by functional end arteries?
Low numbers of cross-branching collateral vessels (Arterio-arterial anastomoses)
What are the symptoms of angina pectoris?
Pain, crushing sensation in the chest
Radiates to neck, arms, jaw with shortness of breath, dizziness
How does angina pectoris feel like?
‘’Strangulation of the chest’’
What are the 3 forms of angina pectoris?
Stable, unstable and variant
What are the causes of angina pectoris?
Causes are ischaemia
What is ischemia in angina pectoris due to?
due to O2 and nutrient demands of cardiac tissue
not being met due to partial occlusion of coronary arteries
What are the causes of increased demands of cardiac tissue
Increased heart rate / left ventricular contractility / wall stress
such as triggers like:
Exercise (increased heart rate, contractility)
hypertension (afterload), left ventricular dilatation (heart failure)
What is stenosis?
partial occlusion
due to plaque formation
What happens to coronary arterioles during exercise in a healthy individual?
In exercise, metabolic vasodilation of
arterioles reduce total R
Increased blood flow to meet
increased O2 demands
What happens in stable angina to coronary arteries and arterioles during rest?
With stenosis in large coronary
artery - Resistance to flow increases
Metabolic vasodilation of arterioles occurs at
rest, so blood flow meets needs
