Coronary Circulation

Coronary Circulation provides blood supply to the heart: 1 -___ circulation in the body 2- ____ arteries 3-Originates from base of __. 4-The coronary arteries and branches: 5-Right and Left interventricular arteries connect at? 6- Anastomoses provides __ circulation so blood can be delivered if one artery is occluded.

1- Shortest 2-Right and Left Coronary 3-Aorta 4-Right Coronary Artery 5-Left Coronary Artery: Circumflex Branch/Artery & Anterior Interventricular Branch (LAD) Artery Apex 6-Colateral.

If total resistance is 20 at rest, and 5 when exercising, what is the increase in blood flow?

4x (20/5 = 4)

Which endothelin receptors lead to vasodilation and in which cells? What about Vasoconstriction?

Endothelin binding to ETB recptors on Endothelial cells, and Endothelin binding to ETA recptors on Smooth Muscle Cells

Why would tachycardia decreases coronary perfusion pressure and coronary blood flow?

It lowers the time spent in diastole.

when would myocardial o2 consumption be greatest? in pressure overloading (aortic stenosis, htn) or volume overloading (aortic regurgitation)?

it would be highest during after load increasing (aortic stenosis or htn), this is b/c mo2 depends more on after load than preload

what does left circumflex artery supply?

left ventricle and left atrium

what is the primary controller of coronary blood flow?

local metabolism (adneosine, co2, K+, pgi2)

What does the L main coronary artery supply?

mainly anterior and left lateral portion of left ventricle (through its branches)

Describe the Coronary Artery Blood Supply of the Heart.

Main coronary arteries lie on the SURFACE of the heart. Smaller arteries then PENETRATE the surface INTO the Cardiac Muscle Mass. LEFT Coronary Artery supplies ANTERIOR & LEFT parts of LV whereas RIGHT Coronary Artery supplies most of the RV.

___ is when coronary flow will increase in proportion to demand (similar to skeletal muscle)

Metabolic hyperemia

Flow at rest is very dependent on?

NO

How does the heart get 70-90% of it's ATP?

Oxidation of fatty acids.

In exercise, metabolic vasodilatation of myocardial resistance vessels increases/reduces downstream resistance

Reduces

Ischemia

Severe _____ can lead to adenosine loss: - Hypoxia - breakdown of ATP to ADP, AMP, adenosine - Release of adenosine from myocytes to blood - dilation - Rapid depletion of adenine base; replacement slow, ~ 2% per hour - diminished adenosine - Cell death occurs within 30 min

Myocardial oxygen consumption

The myocardium extracts nearly all of the oxygen delivered to it from coronary blood flow. -Normal venous oxygen saturation of coronary sinus is 30% -Any increase in oxygen consumption requires an increase in blood flow.

Left anterior descending artery

supplies blood to the front and bottom of the left ventricle and the front of the septum

Circumflex artery

supplies blood to the left atrium and the side and back of the left ventricle

Right coronary artery

supplies blood to the right atrium, right ventricle, bottom portion of the left ventricle and back of the septum

Coronary veins

take oxygen-poor blood that has already been used by muscles of the heart and return it to the right atrium

what is most important for coronary artery filling and why?

the diastolic pressure (of aorta) because, during style, the coronary ostia are partly occluded by aortic valve cusps, so full force of aortic systole never conveyed * how long diastole lasts has an effect on the coronary perfusion pressure >>tachycardia means that coronary blood flow will decline

how does blood from the left ventricle return to right atrium?

through the coronary sinus (via great vein). Once the blood passes through the capillary beds, most of the venous blood returns to the right atrium through the coronary sinus. or by the anterior coronary veins.

how does blood for the right ventricle return to the atrium?

through the small cardiac vein (anterior)>>flows directly to right atrium (not through coronary sinus known as arteriosinusoidal channels ).

How does tachycardia increases cardiac contractility?

By increasing SR calcium loading via the bowditch effect.

How does systemic hypertension and aortic stenosis increase myocardial oxygen requirement?

By increasing afterload.

what does LAD supply??

interventricular septum, LV and portion of RV

Fatty acids

is the principle fuel of cardiac muscle

describe what happens to vasodilation during high HR and contractility?

This will increase the amount of metabolites and therefore vasodilation and high blood flow ** during exercise, this overshadows the alpha 1 receptor vasoconstriction

Types of Cardiac Veins: (2=4 total) Empty directly into right atrium?

Three Large Veins: Great Cardiac Vein (Anterior interventricular sulcus) Middle Cardiac Vein (Posterior interventricular sulcus) Small Cardiac Vein (Right inferior margin) Anterior Cardiac Veins & Coronary Sinus Anterior Cardiac Veins

Acetylcholine

has a direct effect on coronary vessels of dilation and is sent from the vagus

when is mv02 highest and lowest?

highest: isovlumetric contraction lowest: late diastolic filling

what happens to coronary blood flow when ventricular end diastolic pressure abnormally high?

* there will be an increase in diastolic pressure, so the intramural capillaries at subendocardial surface won't get as much blood flow. * if this is superimposed with coronary artery stenosis>>the subendocardial myocardium is at high risk for ischemic injury.

why is there almost no blood flow to coronary arteries during stole?

*ventricular contraction increases vascular resistance in coronary circulation and compresses intramural coronary blood vessels (high extra coronary resistance). * also, there is a little bit of back flow due to the high resistance.

What 3 ways that Arterial Pressure is Increased?

1) Vasoconstriction of Arterioles in tissues of the body not being used 2) Increased pumping activity by the heart 3) Great increase in Mean Systemic Filling Pressure caused by Venous Contraction

Rate of coronary flow increases/decreases as cardiac contraction strength increases/decreases

2 x increases

Cardiac function and myocardial oxygen consumption

1. Cardiac function (at rest) Cardiac Output (CO) ~5 LPM 2. Cardiac reserve (response to exercise) hearts ability to increase blood flow 4x-7x increase with strenuous exercise 3. Myocardial Oxygen consumption (MVO2) 6x-9x increase in oxygen demand

what are special features of the heart that allow it to get enough o2, even when contraction is when blood flow is so low?

1. dense capillaries, and small diameter of cardiac muscle fibers, facilitate o2 diffusion in cardiac cells 2. heart can metabolize a large range of substrates to fulfill demand of ATP (metabolic flexibility) 3. presence of myoglobin (o2 storage molecule that does not diffuse away)

What are the three main things that determine o2 consumption by heart during contraction?

1. heart rate 2. afterload 3. contractility ** preload contributes very small amount

two things involved in autoregulation

1. metabolites 2. endothelium mediated

what supplies SA node?

1. usually RCA 2 in some people the left circumflex

Describe how the arteriovenous oxygen concentration is different in the coronary circulation compared to other regional circulations.

At rest, most organs normally extract ~25% of the oxygen contained within arterial blood and can increase that amount several times if the need arises. In contrast, myocardial O2 extraction is nearly maximal at rest (>75-90%) and the arteriovenous O2 difference across the coronary vascular bed is the largest for any organ.

Blood is collected by__ after it has passed through the heart. Venous blood is collected in the __ which empties into the right atrium.

Cardiac Veins Coronary Sinus

The following are risk factors for ____: - Hypercholesterolemia - Hypertension - Tobacco intake - Obesity - Diabetes

Coronary Atherosclerosis

Coronary Blood flow at rest vs exercise

Coronary blood flow at rest: -225 ml/min (adults) --Can increase to over 1.0 LPM during exercise -5% total cardiac output

Coronary Blood flow

Coronary blood flow reserve -hearts ability to increase coronary flow -Only 3x-4x (Compare to consumption increase of 6-9X)

Atherosclerosis

Deposition of plaque in coronary arteries

What phase is MVO2 lowest in?

Diastolic filling phase.

Adrenaline ___ coronary vessels (B2 adrenoceptors)

Dilates

How does Coronary Blood flow during Systole? Diastole?

During Systole, there is strong compression of the LV muscle around the intramuscular vessels that greatly reduces blood flow to the Coronary arteries. During Diastole, Cardiac muscle relaxes, no longer obstructs blood flow thru the LV muscle capillaries & blood flows rapidly.

Coronary perfusion occurs during diastole

During diastole, aortic diastolic pressure is transmitted without resistance to the coronary ostia. Increased MVO2 is not met with increased blood pressure: Major coronary flow is during diastole: During exercise systolic blood pressure increases but diastolic is mostly unchanged. The coronary arteries receive the great majority of their blood flow during diastole (this will be explained in detail in the next objective). So ABP is not the source of increased coronary blood flow during exercise.

Describe the Coronary Venous blood supply of the heart.

From LV to RA: Coronary Sinus. From RV to RA: Small Anterior Cardiac Veins

How does the heart match oxygen delivery to oxygen consumption?

Higher capillary density, smaller diamter cardiomyocytes, maximum ATP synthesis, myoglobin, and vasodilation

Myocardial O2 Consumption MVO2

In non-diseased coronary vessels, whenever cardiac activity and oxygen consumption increases, there is an increase in coronary blood flow (active hyperemia) that is nearly proportionate to the increase in oxygen consumption. MVO2 is the major determinant of coronary blood flow MVO2 may increase 4-5 times over resting states with exercise In a steady state, MVO2 provides an adequate measure of heart's total metabolism MVO2 of a beating canine heart is 8 - 15 ml/min/100gm MVO2 of noncontracting heart is 1.5 ml/min/100gm

How does tricuspid stenosis decrease CBF?

It increases RAP.

Heart rates above 180-200 decrease what?

Stroke volume and coronary blood flow due to decreased filling time and decreased time spent in diastole.

Metabolic vasodilators normally override ___ ___ ___ of resistance vessels

Sympathetic noradrenergic vasoconstriction

Coronary arteries distribution of blood flow

Typical blood distribution of coronary arteries (right dominant pattern): The LCX supplies the free wall of the LV between the anterior and posterior papillary muscle. The LAD supplies 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 The RCA supplies the free wall of the RV, the posterior 1/3 of the interventricular septum and the posterior wall of the LV to the posterior papillary muscle The leaflets of the mitral valve are tethered to the anterior and posterior papillary muscles in the left ventricle. Failure of the papillary muscles results in acute mitral regurgitation and pulmonary edema. The redundancy of the coronary distribution to the papillary muscles protects against papillary muscle failure resulting from ischemic heart disease by supplying each papillary muscle from two different coronary arteries. The posterior papillary muscle is supplied from the RCA and the LCX arteries. The anterior papillary muscle is supplied from the LAD and the LCX arteries. Diagnostic tests may provide functional information about myocardial wall motion or electrical propagation. Knowing the normal distribution presented here can help you predict which artery has reduced flow.

Sympathetic stimulation of heart leads to ___ of coronary resistance vessels.

Vasodilatation

O2 causes release of ___ from muscle to dilate arteries

Vasodilators Low

What causes an increase in coronary resistance?

Ventricular contraction, compressing intramural coronary vessels. Therefore resistance is highest in ejection phase, and within the left ventricle. Increased left ventricular end diastolic pressure can compress intramural capillaries at subendocardial surface as well, causing coronary artery stenosis.

How is CBF autoregulated?

Via NO, and an increase in MVO2 which causes vasodilation through adenosine and other metabolites like H+, CO2 K_ PGI2 and KATP channels

Noradrenaline, adrenaline

___ and ___ have a direct effect on coronary vessels of activating adrenergic receptors on coronary vessels

why is ischemia of subepicardial myocardium less likely?

because it is adjacent to large epicardial coronary arteries, and so will get a greater proportion of blood flow

Vagal stim (Ach)

can indirectly effect coronary vessels by decreasing heart rate, contractility, O2 consumption. Constricts arteries

Sympathetic (NE and Epi)

can indirectly effect coronary vessels by increasing heart rate, contractility, metabolism. It dilates arteries and increases blood flow in proportion to metabolic need of cardiac muscle

endothelin

counteracts actions of NO (vasoconstrictor of vascular endothelium) * it bind receptor during shear stress as well and will increase angiotensin II and catecholamines. * activates PLC>>IP3, high Ca2+= contraction to counteract NO

Left Coronary Artery

divides into two branches: the circumflex artery and the left anterior descending artery

Cardiac efficiency must ___to avoid myocardial oxygen debt!

double

O2 demand

drives local coronary blood flow