Coronary Arteries Flashcards
The right coronary artery is dominant is what percentage of people?
In 85% of individuals, the RCA supplies the posterior descending artery (PDA)
The left main coronary artery divides into what?
- Left anterior descending (LAD): widow maker
- Left circumflex
-Ramus intermedius
In 37% of people there is a trifurcation of left main
What is normal coronary blood flow?
70mL/100grams
About 5% of CO
Bulk of coronary blood flow is during diastole
What contributes most to the coronary vascular resistance?
Intramyocardial vessels
The epicardial conductance vessels are larger and on the surface. Only contribute a small percentage of resistance normally
What is the main determinant of myocardial oxygen supply?
Metabolic activity
How does a faster HR affect coronary blood flow?
A faster HR shortens diastole which decreases the amount of time for coronary blood flow
Which organ uses the most O2 while at rest?
Cardiac muscle: 9.7mL/100g/min
Next closest is kidneys at 6.0mL/100g/min
What is coronary perfusion pressure
Pressure gradient that drives blood though the coronary circulation
Coronary perfusion pressure =
DBP-LVEDP (or PCWP)
T/F: The heart extracts O2 to a greater extent than any other organ
True
Coronary sinus pO2 is normal 20-22mmHg (%sat 32-38)
-this is where 75% of venous return from myocardium goes
Bc can’t extract more O2, if there is an increase in demand, must increase coronary blood flow
Increased O2 demand results in lower tissue O2 tension. This causes _________
Vasodilation and increased blood flow
What is autoregulation?
Ability of a vascular network to maintain constant blood flow over a range of arterial pressures
It is an independent determinant of CBF
The set point at which CBF is maintained depends on MVO2
What is the most important endothelial method for controlling coronary vascular tone?
Nitric oxide —->cGMP
Damage to endothelial cells will lead to?
This will ultimately cause?
- decreases Nitric Oxide and Prostacyclin production
- Increased Endothelin production
- vasoconstriction
- vasospasm
- thrombosis
Coronary blood flow is controlled predominantly by what 3 factors?
- Local metabolic
- Autoregulatory
- Endothelial
Sympathetic stimulation releases what from the sympathetic nerves and adrenal medullae to increase HR and contractility?
Epi
Epi and norepinephrine
*Increases the rate of metabolism of the heart
Direct effect
This is an indirect effect of increasing the rate of metabolism of the heart
Blood flow increases in proportion to the metabolic needs of the heart muscle
Vagal stimulation releases what which slows the heart and has a slight depressive effect on heart contractility?
Acetylcholine
These effects decrease cardiac O2 consumption and therefore indirectly constrict the coronary arteries
Contrast
During sympathetic stimulation, epi and norepinephrine
Do what to alpha and beta receptors in coronary vessels?
Alpha: constrict coronary vessels
(Larger vessels have more alpha)
Beta: dilate coronary vessels
(Smaller vessels have more Beta)
-Beta 1: in conduit arteries
-Beta 2: in resistance arteries
During parasympathetic stimulation, acetylcholine does what?
Vasodilation in healthy subjects
Vasoconstriction in pts with atherosclerosis (occurs once endothelial layer is damaged)
Because of __________. ________ the endocardium is more susceptible to ischemia, especially at lower perfusion pressure
Extravascular compression
The effect of extravascular compression is felt most at what point of the cardiac cycle?
Early systole
Bc aortic pressure, which is the main force maintaining vascular patency, is at a low point
Systolic blood flow constitutes a much greater proportion of total blood flow to what area of the heart and why?
The right ventricle
Due to lower pressures generated by thin right ventricle in systole
What are the subendocardium and subepicardial layer?
Subendocardium: inner layer of myocardium
Subepicaridal: outer layer of myocardium
Extravascular compressive forces are greater in the inner or outer layer?
Inner layer
Which layer of the myocardium is more susceptible to ischemia?
Subendocardial layer
Epicardial coronary stenoses are associates with what?
Reductions in the subendocardial to subepicaridal flow ratio
Normal ratio is 1.25:1
In the absence of CAD, maximal flow is ________x as great as at rest
4-5
Coronary flow respecter decreases with increasing severity of CAD
Myocardial O2 consumption is defined as
The volume of O2 consumed per minute
(Usually expressed per 100g of tissue weight)
A resting heart uses 8mLO2/min per 100g
Factors that increase myocardial O2 consumption
- increased HR main one
- increased inotropy
- increased afterload
- increased preload affects least
Is pressure of volume work more costly regarding oxygen cost of myocardial work?
Pressure work
Myocardial ischemia upsets the balance of what electrolytes?
Na and K
There is a decrease in Na-k ATPase activity which leads to an increase in intracellular Na, a decreased Na/Ca exchanged, and an overload of intracellular CA++
This leads to impaired contractility and eventually cell death
There is an intracellular overload of what electrolyte during myocardial ischemia
Calcium
Systolic dysfunction
Ischemia causes alterations that may range from minimal impact to absence of movement (akinesis) to systolic lengthening and post-systolic shortening (dyskinesia)
In left ventricular failure, the flow volume loop moves what direction?
Narrows and moves to the right
How does left ventricular failure affect the frank-starling curve?
EDP increases, but stroke volume goes down
What are key features of a healthy heart?
Normal heart structure
Normal heart function
Fatty acid oxidation
What are key features of compensated hypertrophy?
- LV hypertrophy and thickening
- Alterations in Ca++ handling
- Switch to glucose utilization
- Fibrosis
What are key features of decompensated hypertrophy and heart failure?
- LV dilation
- cardiac dysfunction
- apoptosis
- EKG changes
- excessive fibrosis
- inadequate angiogenesis
- excessive autophagy
- energy deplete
Diastolic dysfunction
When a sufficient amount of myocardium is rendered ischemic, LVEDP rises
Relaxation is impaired and myocardial compliance decreases
What are the 4 phases of diastolic dysfunction and which is irreversible?
- Impaired relaxation
- Pseudonormalization
- Restrictive filling (reversible)
- Restrictive filling (irreversible)
What does the flow volume look like with left ventricular diastolic failure?
Smaller and shift to the left
Myocardial stunning
After a brief episode of severe ischemia, prolonged myocardial dysfunction with gradual return of contractile activity occurs
*duration of reduced performance is dependent on duration of ischemia. Reversible
Myocardial hibernation
Presence of impaired resting LV function, owing to reduced CBF that can be restored toward normal by revascularization
*seen in chronic ischemia
What are some things that can result from myocardial ischemia?
Systolic/diastolic dysfunction Angina CHF/pulmonary edema Arrhythmias MI Ventricular rupture or VSD Cardiogenic shock Death
Drugs used to treat ischemia
O2 Beta-blockers Nitrates Antiplatelet/anticoagulant Analgesics Calcium-channel blockers
What interventions can be done to treat myocardial ischemia?
CABG
-gold standard
Percutaneous coronary interventions
- coronary balloon angioplasty
- bare-metal coronary stents
- drug-eluding stents
How long should you wait before doing elective surgery after PCI?
Bare metal stent
-cardiac complications are lowest after 90 days
Drug-eluting stent
-1 year is recommended
Name some examples of perioperative medical therapy
Volatile anesthetic agents -anesthetic preconditioning Beta-blockers Statins -stabilize plaque -anti-inflammatory Alpha-2 agonists -clonidine -useful in pts not able to take beta-blockers (asthmatics_ calcium channel blockers nitroglycerin -use prophylactically unclear if changed in outcome
Collateral blood flow
Develop in response to impairment of coronary blood flow
Develops between occluded and non-occluded branches
Originate from pre-existing arteries that undergo proliferation changes of the endothelium and smooth muscle
Ischemic preconditioning
Brief periods of ischemia can be protective agains a subsequent prolonged ischemic insult
- inhaled agents have effects that mimic IPC
- K+ATP channels play an important role
