Ischaemic Heart Disease Flashcards
What is coronary circulation? Why is it needed?
cardiomyocytes have a high demand for nutrients and oxygen to keep the heart beating
muscle thickness of the ventricles means that only the first layers of cells receive nutrients by diffusion alone
an expansive network of blood vessels is needed to deliver blood to the heart
Where does coronary circulation deliver blood to?
arises in the aortic sinus - are dilations of the aorta just above the left ventricle and aorta/aortic valve, give rise to the left and right coronary artery
right coronary artery - supplies blood to the right ventricle, right atrium and nodes (SAN and AVN)
left coronary artery - gives rise to the left circumflex artery and left anterior descending artery
left circumflex artery - supplies blood to the outer and back side of the heart
left anterior descending artery - supplies blood to the front side of the heart
What are the features of coronary circulation?
must maintain a high basal rate of oxygen supply
- high capillary density
- high oxygen extraction
increase in supply is proportional to increased cardiac demand
- coronary circulation responds to build up of metabolites by vasodilation as they cause relaxation
What are the problems with coronary circulation?
oxygen extraction is already at a high rate (75%)
- more oxygen cannot be extracted when required as its already at maximum extraction
systole impairs coronary perfusion (passage of blood)
- during systole, the coronary arteries are compressed
= results in momentary reduction of blood flow and back flow to the aorta
coronary arteries are end arteries
- have very little side branches = anastomoses
- blockage of the branch leads to no oxygen supply to its tissues
What factors lead to poor myocardial perfusion?
coronary artery narrowing
- atheroma formation, thrombus and vasospasm
aortic valve stenosis
increased heart rate
How does coronary artery narrowing lead to poor myocardial perfusion?
atheroma formation
- endothelial damage occurs, LDL and fibrin deposition increases, platelet aggregation occurs, smooth muscle cell proliferation and expansion and foam cells
= reduced lumen diameter leads to reduced blood supply
thrombus
- risk of thrombus is increased by atheroma
vasospasm
- narrowing is caused by persistent contraction of the arteries
How does aortic stenosis lead to poor myocardial perfusion?
occurs when the aortic valve does not open fully
- as coronary circulation starts at the aortic valve, if it doesn’t function properly it can cause back flow of blood and reduced myocardial perfusion as a result
How does increased heart rate lead to myocardial perfusion?
increased heart reduces myocardial perfusion due to increased systole
- systole causes compression of the coronary arteries
What is angina? What are its symptoms?
angina is the pain associated with reversible ischaemia
squeezing, heaviness, tightness in the chest
What are the types of angina?
stable angina
- exertion induced
- linked to atheroma
unstable angina
- not usually induced by exertion
- linked to atheroma = plaque rupture or thrombus can quickly block/reduce blood flow
variant/prinzmetal
- caused by a sudden spasm in the artery due to smooth muscle contraction = often occurs at rest
How can angina be diagnosed?
ECG
Angiogram
Biochemical markers = are elevated during damage
- aspartate transaminase, lactate dehydrogenase, creatine kinase and troponin C
What are the pharmacological treatments for angina?
beta blockers - atenolol
nitrate - glyceryl trinitrate, isosorbide denigrate
calcium channel antagonists - dihydropyridines (amlopdipine), benzothizepines (diltiazem), diphenylalkylamines (verapamil)
How do beta blockers act?
slows heart rate by blocking the effects of catecholamines (adrenaline/noradrenaline) at the beta-1 adrenoceptors
- decreases sympathetic activity
prevents response to exercise
reduces force of contraction
reduces arterial blood pressure
decreases demand and increases perfusion
How do nitrates act?
are nitric oxide donors
binds to and activates soluble guanylyl cyclase
- catalyses the phosphorylation of GTP (guanosine triphosphate) to cGMP (cyclic guanosine monophosphate)
cGMP is a second messenger
- induces smooth muscle relaxation by blocking calcium entry into cells, decreasing intracellular sodium
is veno selective = effective at large veins
- causes vasodilation = relaxation means less stretching, less work, less blood coming back
- reduces cardiac load and improves coronary perfusion due to reduced compression of arteries
How do calcium channel antagonists work?
slows heart rate
- decreased after load through arterial dilation, aids coronary perfusion
inhibit calcium influx to vascular smooth muscle cells, cardiomyocytes and conducting cells
