Coronary Circulation

Question 1

Describe the coronary anatomy

Answer 1

Review pgs. 44 - 53

Question 2

Describe the normal distribution of coronary blood flow

Answer 2

Review pgs. 52 - 54

Question 3

Discuss the variables influencing coronary blood flow

Answer 3

I could review pgs. 55 - 70, but the notes are bad SO DONT. I did my best to make flashcards of all of the main points in this learning objective.

NOTE THAT HE EDITED HIS NOTES–I HAVE THE POWERPOINT IN THE FOLDER, SO LOOK @ THAT. ALSO, CHECK TO SEE IF THERE IS A QUIZ YET.

Question 4

Briefly describe clinical approaches to diagnose and improve myocardial perfusion

Answer 4

The notes are bad (SO DO NOT READ), I did my best to make flashcards of all of the main points in this learning objective.

Question 5

What is a right dominant heart?

Answer 5

If the posterior descending artery (PDA) (a.k.a. posterior interventricular artery) is supplied by the right coronary artery (RCA), then the coronary circulation can be classified as “right-dominant”. Most common.

Question 6

What is a left dominant heart?

Answer 6

If the posterior descending artery (PDA) is supplied by the circumflex artery (LCX=Circumfex artery), a branch of the left coronary artery, then the coronary circulation can be classified as “left-dominant”.

Question 7

What is a co-dominant heart?

Answer 7

If the posterior descending artery (PDA) is supplied by both the right coronary artery (RCA) and the circumflex artery, then the coronary circulation can be classified as “co-dominant”.

Question 8

Describe coronary artery dominance.

Answer 8

“Coronary Dominance” The posterior descending artery (PDA, AKA: posterior interventricular artery) travels in the posterior interventricular groove to the apex of the heart

70% PDA supplied by the right coronary artery, RCA (right dominance)

20% PDA Supplied by both the RCA and the LCX (co-dominant)

10% PDA Supplied by the Circumfex artery LCX (left dominant)

Question 9

The posterior papillary muscle is supplied form the ___ and the ___ arteries.

Answer 9

The posterior papillary muscle is supplied form the RCA and the LCX arteries.

Question 10

The anterior papillary muscle is supplied form the ___ and the ___ arteries.

Answer 10

The anterior papillary muscle is supplied form the LAD and the LCX arteries.

Question 11

Discuss the structure of the papillary muscles, what their failure results in, & how their failure is overcome anatomically.

Answer 11

The leaflets of the mitral valve are tethered to the anterior and posterior papilary muscles in the left ventricle.

Failure of the papilary muscles results in acute mitral regurgitation and pulmonary edema. The coronary circulation protects against papilary muscle failure resulting from ischemic heart disease by supplying each papilary muscle from two different coronary arteries.

Question 12

In Perfusion for the equation P=QR

perfusion is to which variable?

What type of blood pressure do we use for P (or when does perfusion occur)?

What elements give resistance?

Answer 12

Perfusion = Q, blood flow

P = Diastolic BP, perfusion occurs in diastole when the heart relaxes & the coronary arteries fill w blood

Resistance = mechanical, pathologic, & metabolic

Question 13

The heart’s myocardium consumes ____ of the blood delivered to it via the coronary blood flow. So an increase in oxygen consumption requires an _____ in blood flow.

Answer 13

The heart’s myocardium consumes nearly all* of the blood delivered to it via the coronary blood flow. So an increase in oxygen consumption requires an increase* in blood flow.

Question 14

What is autoregulation of coronary flow?

Answer 14

Autoregulation is the intrinsic ability of the heart to maintain a constant blood flow over a wide range of coronary perfusion pressures. The coronary arteries do this by changing their resistances since the pressure is constant in a certain range to facilitate perfusion. Resistance changes occur in mechanical, pathologic, & metabolic resistance forms.

Question 15

Mechanical resistance

Answer 15

Occurs as blood flows in the vessel by being squeezed by the muscle

Question 16

What are the 2 mechanisms of autoregulation

Answer 16

Metabolic control

Myogenic control

Question 17

Describe metabolic control mechanisms

Answer 17

Metabolic control: result of local metabolism, may be due to NO mediated dilation, or the endothelium may sense pressure changes through pressure sensitive ion channels.

Question 18

Describe myogenic control

Answer 18

Myogenic control: arteriolar vascular smooth muscle contracts with increased intra-luminal pressure.

Question 19

Preload

Answer 19

Filling pressure or the amount of stretch on a muscle just before contraction. It can give the optimal stretch for starlings curve for the best contractile force (sensitivity). MV stenosis or regurgitation reduces preload–aortic insufficiency also reduces preload.

Question 20

Afterload

Answer 20

The pressure or resistance the heart is working against while it is squeezing. Stenosis increases afterload so the heart has to work harder.

Question 21

MVO2 =

Answer 21

myocardial oxygen consumption

Question 22

Pathologies influencing MVO2 & myocardial perfusion

Answer 22

Coronary artery disease

ventricular hypertrophy

ventricular dilation

Coronary fistula

Question 23

Athlerosclerosis (typically 75% occlusion) affects the arteries in terms of P=QR by?

Describe the downstream effects of the plaque.

Answer 23

It reduces Q & P

It increases the resistance R

Downstream to the plaque the arterioles will dilate to try to get more perfusion or flow Q.

At the point to where you cannot auto-regulate anymore via dilation, then perfusion is based on pressure, & since pressure is low you get ischemia.

Ischemia is most present during systole because the subendocardium is not perfused as well (the left ventricle is more subjected to subendocardial ischemia since it has higher operating pressures than the right ventricle).

Question 24

Ischemia

Answer 24

is a restriction in blood supply to tissues, causing a shortage of oxygen needed for cellular metabolism

Question 25

Ventricular fibrilation

Answer 25

Ventricular fibrillation (V-fib or VF) is a condition in which there is uncoordinated contraction of the cardiac muscle of the ventricles in the heart, making them quiver rather than contract properly. Ventricular fibrillation is the most commonly identified arrhythmia in cardiac arrest patients. Consequently, the heart will eventually stop pumping (beating) & your BP will drop & death will occur soon. It can be the result of coronary artery disease (typically 75% occlusion needed).

Question 26

The result of a blocked LAD by athlerosclerosis in heart disease can cause?

Answer 26

Myocardial infarction

MI happens when blood stops flowing properly to part of the heart and the heart muscle is injured due to not receiving enough oxygen & this results in the necrosis of downstream myocardium.

Question 27

Define coronary flow reserve.

How does coronary flow reserve pressure change with stenosis?

Answer 27

Coronary flow reserve (CFR) is the maximum increase in blood flow through the coronary arteries above the normal resting volume.[1] Its measurement is often used in medicine to assist in the treatment of conditions affecting the coronary arteries and to determine the efficacy of treatments used.

Increasing stenosis severity causes increasing coronary flow reserve pressure drop. Coronary flow is limited with stenosis so that a person with stenosis that never exercises might never produce symptoms; however, if they increase their exercise level and call on their coronary flow reserve, they will not be able to (this produces chest pain).

See pg. 67

Question 28

What condition can produce ventricular hypertrophy?

Answer 28

aortic stenosis

The heart needs more muscle to work harder to push blood through the stenotic aorta

Question 29

By giving vasodilatroy drugs like Nitroglycerine or Adenosine, we can increase perfusion by

Answer 29

reducing resistance to flow

Question 30

Describe angiograms

Answer 30

The radiopaque dye filling the arteries makes the lumen of the arteries visible. They can indicate areas where atherosclerotic plaques are reducing the diameter of the vessel.

Question 31

Describe angioplasty with a stent

Answer 31

Angioplasty is the technique of mechanically widening narrowed or obstructed arteries, the latter typically being a result of atherosclerosis. An empty and collapsed balloon on a guide wire, known as a balloon catheter, is passed into the narrowed locations and then inflated to a fixed size using water pressures some 75 to 500 times normal blood pressure (6 to 20 atmospheres). The balloon forces expansion of the inner white blood cell/clot plaque deposits and the surrounding muscular wall, opening up the blood vessel for improved flow, and the balloon is then deflated and withdrawn. A metal stent (metal tube) may or may not be inserted at the time of ballooning to ensure the vessel remains open.

Question 32

Describe coronary artery bypass surgery

Answer 32

Coronary artery bypass surgery is a surgical procedure performed to relieve angina and reduce the risk of death from coronary artery disease. Arteries or veins from elsewhere in the patient’s body are grafted to the coronary arteries to bypass atherosclerotic narrowings and improve the blood supply to the coronary circulation distal to the occlusion to supply the myocardium (heart muscle).

Question 33

Describe the Prophylactic intra-aortic balloon pump

Answer 33

If you have poor myocardial perfusion, this intervention can improve perfusion with diastolic augmentation and afterload reduction.

The balloon pump is laced into the aorta & it is synchronized with your rhythm of your heart. So when your heart goes in to systole the balloon collapses & gets out of the way. While it is collapsing it is creating a space so the blood around it rushes into & blood pressure drops. The heart will now eject at a lower pressure & we reduced afterload & made it easier for the heart to eject (less work). Now when the heart goes into diastole, the baloon inflates & raises the diastolic BP by displacing the blood to give better perfusion (remember that the coronary arteries come off the aorta), which increases oxygen supply to the heart.

Question 34

Discuss the clinical use of controlled cardiac arrest

Answer 34

The hearts electrical rhythm and mechanical contraction can be arrested electively for cardiac surgery. Cardioplegic solution is infused into the coronary arteries to raise the resting membrane potential of the myocytes above their natural threshold limit. Subsequently the heart is arrested in diastole and becomes motionless.

Generally the cardioplegic solution is delivered at very low temperatures. The combination of asystole and hypothermia reduces the MVO2 by nearly 97% and hearts can be preserved without further perfusion for “extended” periods of time.

During Cardiac surgery hearts may be arrested for several hours with only intermittent perfusion every 20-30 minutes. In the case of living heart donors, hearts are arrested prior to harvest and preserved unperfused for up to 6 hours during the transport and re-implantation.

Question 35

Both _____ and _____ are potent vasodilators. Resting coronary flow is reduced starting when a coronary artery stenosis results in ______ reduction in vessel diameter. The coronary artery _______ is a primary regulator of coronary vascular resistance. Coronary blood flow is ________.

Answer 35

Both nitric oxide and adenosine are potent vasodilators. Resting coronary flow is reduced starting when a coronary artery stenosis results in ~70-90% reduction in vessel diameter. The coronary artery endothelium is a primary regulator of coronary vascular resistance. Coronary blood flow is autoregulated.

Question 36

Systolic compression has much less effect on flow through the ______ ventricular myocardium than the ______. The myocardium extracts _______of the oxygen delivered to it from coronary blood flow. In the left coronary artery, more flow occurs during _____ than during _______. In the right coronary artery, flow is fairly _____ during systole and diastole.

Answer 36

Systolic compression has much less effect on flow through the right ventricular myocardium than the left. The myocardium extracts nearly all of the oxygen delivered to it from coronary blood flow. In the left coronary artery, more flow occurs during diastole than during systole. In the right coronary artery, flow is fairly even during systole and diastole.

Question 37

Negative flow (back flow) is common during ______. The occlusive force exerted on the coronary vessels during ventricular systole is greatest at the ________ portion. For this reason, this is the part of the myocardium most prone to ischemic damage and subsequent infarction. Eddy currents (i.e., turbulence) prevent the cusps from ______ the coronary arteries.

Answer 37

Negative flow (back flow) is common during systole. The occlusive force exerted on the coronary vessels during ventricular systole is greatest at the subendocardial portion. For this reason, this is the part of the myocardium most prone to ischemic damage and subsequent infarction. Eddy currents (i.e., turbulence) prevent the cusps from occluding the coronary arteries.

Question 38

Coronary resistance vessels are controlled by the needs of the myocardium via changes in local metabolite concentrations, especially ______. Lactic acid also causes _______ but to a lesser degree than _______. The shear stress caused by high velocity flow can cause vasodilation via ______ release but is unlikely in the setting of decreased perfusion and angina. The parasympathetic nervous system does ______ in coronary vessel regulation, whereas norepinephrine _________ blood vessels.

Answer 38

Coronary resistance vessels are controlled by the needs of the myocardium via changes in local metabolite concentrations, especially adenosine. Lactic acid also causes vasodilation but to a lesser degree than adenosine. The shear stress caused by high velocity flow can cause vasodilation via nitric oxide release but is unlikely in the setting of decreased perfusion and angina. The parasympathetic nervous system does not have any significant role in coronary vessel regulation, whereas norepinephrine constricts blood vessels.

Question 39

Nitrates are first-line treatment in the management of angina. They act by stimulating the release of ______ in smooth muscle, causing an increase in cGMP levels and subsequent smooth muscle _____, primarily in the ______ system. Such _______ causes a decrease in preload, which reduces left ventricular wall stress and in turn minimizes myocardial oxygen consumption.

Answer 39

Nitrates are first-line treatment in the management of angina. They act by stimulating the release of nitric oxide in smooth muscle, causing an increase in cGMP levels and subsequent smooth muscle relaxation, primarily in the venous system. Such venodilation causes a decrease in preload, which reduces left ventricular wall stress and in turn minimizes myocardial oxygen consumption.

Question 40

The right coronary artery (RCA) arises from the aortic sinus of the ascending aorta and runs along the right side of the pulmonary trunk in the coronary groove. It gives off a sinoatrial (SA) nodal branch, the acute marginal artery, and an atrioventricular (AV) nodal branch. About 80% of people have “right dominant” circulation, meaning the RCA also gives off the posterior descending artery, which supplies the _______ and _______ ventricles and the posterior one-third of the _______.

Answer 40

The right coronary artery (RCA) arises from the aortic sinus of the ascending aorta and runs along the right side of the pulmonary trunk in the coronary groove. It gives off a sinoatrial (SA) nodal branch, the acute marginal artery, and an atrioventricular (AV) nodal branch. About 80% of people have “right dominant” circulation, meaning the RCA also gives off the posterior descending artery, which supplies the posterior and inferior ventricles and the posterior one-third of the interventricular septum.

Question 41

The left anterior descending (LAD) artery branches from the left main coronary artery as it approaches the AV junction. It descends toward the apex on the anterior wall of the heart between the right and left ventricles and supplies the anterior wall of _______ and the anterior two-thirds of the _______, including the AV bundle.

Answer 41

The left anterior descending (LAD) artery branches from the left main coronary artery as it approaches the AV junction. It descends toward the apex on the anterior wall of the heart between the right and left ventricles and supplies the anterior wall of both ventricles and the anterior two-thirds of the interventicular septum, including the AV bundle.

Question 42

Discuss conditions that increase the probability of coronary artery disease.

Answer 42

There are several factors that increase the risk of coronary artery disease, including physical inactivity, diabetes mellitus, hypertension, and aging. Increases in body weight also increase the risk of coronary artery disease.

Decreases in body weight reduce the risk of coronary artery disease.

Question 43

Which of the following vasoactive agents is usually the most important controller of coronary blood flow?

Answer 43

Adenosine

Question 44

During systole, the percentage decrease in subendocardial flow is ______ than the percentage decrease in epicardial flow.

Answer 44

greater

The normal resting coronary blood flow is approximately 225 ml/min. Infusion of adenosine or local release of adenosine normally increases the coronary blood flow. The contraction of the cardiac muscle around the vasculature, particularly in the subendocardial vessels, causes a decrease in blood flow. Therefore, during the systolic phase of the cardiac cycle, the subendocardial flow clearly decreases, and the decrease in epicardial flow is relatively minor.

Question 45

Several factors contribute to decreased coronary flow in patients with ischemic heart disease. Some patients have ______ of the coronary arteries, which acutely decreased coronary flow. However, the major cause of decreased coronary flow is an _______ narrowing of the lumen of the coronary arteries.

Answer 45

Several factors contribute to decreased coronary flow in patients with ischemic heart disease. Some patients have spasm of the coronary arteries, which acutely decreased coronary flow. However, the major cause of decreased coronary flow is an atherosclerotic narrowing of the lumen of the coronary arteries.