Coronary Arteries Flashcards by Art Vandelay

The right coronary artery is dominant is what percentage of people?

In 85% of individuals, the RCA supplies the posterior descending artery (PDA)

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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

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What is normal coronary blood flow?

70mL/100grams

About 5% of CO

Bulk of coronary blood flow is during diastole

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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

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What is the main determinant of myocardial oxygen supply?

Metabolic activity

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How does a faster HR affect coronary blood flow?

A faster HR shortens diastole which decreases the amount of time for coronary blood flow

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Which organ uses the most O2 while at rest?

Cardiac muscle: 9.7mL/100g/min

Next closest is kidneys at 6.0mL/100g/min

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What is coronary perfusion pressure

Pressure gradient that drives blood though the coronary circulation

Coronary perfusion pressure =

DBP-LVEDP (or PCWP)

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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

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Increased O2 demand results in lower tissue O2 tension. This causes _________

Vasodilation and increased blood flow

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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

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What is the most important endothelial method for controlling coronary vascular tone?

Nitric oxide —->cGMP

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Damage to endothelial cells will lead to?

This will ultimately cause?

decreases Nitric Oxide and Prostacyclin production
Increased Endothelin production
vasoconstriction
vasospasm
thrombosis

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Coronary blood flow is controlled predominantly by what 3 factors?

Local metabolic
Autoregulatory
Endothelial

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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

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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

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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

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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

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During parasympathetic stimulation, acetylcholine does what?

Vasodilation in healthy subjects

Vasoconstriction in pts with atherosclerosis (occurs once endothelial layer is damaged)

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Because of __________. ________ the endocardium is more susceptible to ischemia, especially at lower perfusion pressure

Extravascular compression

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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?

1. Impaired relaxation 2. Pseudonormalization 3. Restrictive filling (reversible) 4. 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