Coronary Circulation Flashcards
What are the two major arteries of the heart?
The right coronary and the Left coronary
What is a major branch of the right coronary?
acute marginal
What are the major branches of the left main coronary artery?
1- LAD
2- Circumflex artery
3- Ramus intermedians
Venous drainage of the myocardium is predominantly to the ________________ via the _______________.
It is predominantly to the right atrium via the coronary sinus
What are thebesian vessels?
vessels connecting cardiac chambers to arterioles, capillaries and venules
Which chamber of the heart recieves the majority of thebesian drainage?
The Right Atrium
What are the three normal anatomical varients?
1- coronary dominance
2- single ostia
3- extra ostia
Is there any interconnectivity between coronary vessels?
Yes
1- arterial to venous shunts
2- arerial to arterial connections
3- venous to venous connections
Is coronary circulation a simple loop?
No, it is not….interconnections are present
What section of the left ventricle free wall is supplied by the left circumflex?
the section between the anterior and posterior papilary muscle
What does the LAD supply?
The free wall of the LV, the anterior 2/3 of the ventricular septum and a small portion of the free wall of the RV
What does the right coronary artery supply?
the free wall of the RV, the posterior 1/3 of the interventricular septum and the posterior wall of the Left ventricle to the posterior papilary muscle
Failure of the papilary muscle results in what?
It results in acute mitral regurgitation and pulmonary edema
What protects against papilary muscle failure resulting from ischemic heart disease?
coronary circulation
When does coronary perfusion occur?
It occurs during diastole
Where and when does maximum flow occur?
Maximum flow occurs in the left coronary artery during early diastole
Perfusion = ?
blood flow (Q)
How much oxygen does the myocardium extracts from coronary blood flow?
Nearly all of the oxygen delivered to it
Coronary blood flow is determined by:
1) the driving pressure through the coronary vessel
2) the resistance of the coronary vessels
How does P (Pressure) influence Q (Perfusion)?
Increasing Pressure erults in increasing perfusion
What is autoregulation?
Autoregulation is the intrinsic ability of the heart to maintain a constant blood flow over a wide range of coronary perfusion pressures.
What is coronary flow reserve?
the maximal increase in coronary blood flow above its resting level for a given perfusion pressure when coronary vasculature is maximally dilated
What causes a reduction in coronary flow reserve?
epicardial coronary artery stenosis or coronary microvascular dysfuction
What impairs autoregulation?
1- critical fall in aortic pressure
2- chronic hypertension and LV hypertrophy
What are the two general mechanisms of autoregulation?
1- Metabolic mechanisms
2- Myogenic mechanisms
What are some metabolic mechanisms for autoregulation?
- result of local metabolism
- may be due to NO mediated dilation
- endothelium senses changes in pressure through pressure-sensitive ion channels
What is an example of myogenic control in autoregulation?
arteriolar VSM contracts with increased intraluminal pressure
What are some powerful vasodilators that endothelium produces?
1- Endothelium derived relaxing factor (EDRF)
2- NO
3-Prostacyclin
4- Endothelium derived hyperpolarizing factor (EDHF)
What are some risk factors associated with impaired endothelium dysfunction?
1- Hypertension 2- Diabetes mellitus 3- Smoking 4- Menopause 5- Dense LDL 6- Aging 7- Hyperhomocystenemia
How is NO produced?
From the amino acid L-arginine by the enzymatic action of nitric oxide synthase (NOS) in the vascular endothelium
What stimulates NO production?
Increased blood flow stimulates NO formation (flow-dependent NO formation) because shear force on the vascular endothelium causes a release of calcium and cNOS activation.
What can inhibition of NO cause?
Inhibition of NO can cause vasoconstriction
What is preload?
The filling pressure (the amount of stretch on muscle just before contraction)
What is afterload?
This is the pressure/ resistance the heart is working against while it is squeezing
What is a major determinant of coronary blood flow?
mixed venous oxygen saturation (MVO2)
Do preload and afterload influence MVO2?
yes
What pathologies influence preload?
Mitral valve stenosis, mitral valve regurgitation, aortic insufficiency
What pathologies influence afterload?
aortic stenosis, HNT
What are four pathologies that e?ffect MVO2
CAD, Ventricular hypertrophy, Ventricular dilation,
Coronary fistula
What is the definition of ischemia?
imbalance between myocardial oxygen supply and demand
Describe supply ischemia:
Increased coronary vascular tone
Intracoronary platelet aggregation
Thrombus formation
What are three general examples of ischemia?
Supply ischemia, demand ischemia, hypoxia
What is the definition of demand ischemia?
Increase in coronary blood flow that is insufficient to meet the increase myocardial O2 demand
What maintains constant flow with increasing stenosis severity?
autoregulation
What is the effect of ventricular hypertrophy on coronary flow reserve?
it reduces coronary flow reserve
Does myocardial mass increase or decrease with Left Ventricular hypertrophy?
It increases
What are three ways to assess coronary blood flow?
coronary angiogram, magnetic resonance angiogram, computed tomography angiogram
What are some pharmacologic methods of improving coronary blood flow?
Nitroglycerine, adenosime
What are two invasive methods of improving coronary blood flow?
angioplasty (with stent) and CAGB
What are the limitations of angioplasty?
Invasive, potential underestimation of lesion severity, no information on hemodynamic significance, no information on vessel wall
What are some pharmacological vasodilators?
Nitroglycerine, dipyridamole, papaverine, adenosine, NO
What are the three main mechanisms of nitroglycerine?
1-Dilates epicardial conduit arteries and small coronary resistance vessels
2-Improves subendocardial perfusion by reducing LV end-diastolic pressure by venodilation
3-Dilates coronary collateral vessels
These three facts describe what vasodilator?
1-Inhibits the myocyte reuptake of adenosine released locally
2-Mechanism of action similar to adenosine
3-Reversed by adenosine receptor antagonists—aminophylline
dipyridamole
What type of cells can release adenosine?
cardiac myocytes
Does adenosine have a direct effect on larger arteries?
No
What enzyme is needed in the synthesis of NO from L- arginine?
Nitric oxide synthase
Is NO produced intermittently or continually?
Continually
What stimulates NO formation?
Increased blood flow, because shear force on the vascuar endothelium causes a release of calcium and cNOS ativation
What does inhibition of NO cause?
vasoconstriction and reduction in the magnitude of metabolic dilation
Does hypoxia increase or decrease the production of NO?
increase production
How does the intra aortic balloon pump (a cardiac assist device? improve cardiac function?
1- reduction of afterload
2- diastolic augmentation
How does cardioplegic solution effect resting membrane potential of the myocytes?
Increase it about their natural threshold
