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CVS disordersaboutisToday's lecture

:)1(Ischemia

Anatomical and Physiological Introduction:-

Heart arteries are mainly 2 and they arise from the

ascending aorta (which is the largest art. In human) and

supply the myocardium with oxygenated blood:

1- Left Coronary art. Divides into:

-anterior interventricular branch.

-circumflex branch.

2- Right Coronary art. Divides into:

- posterior interventricular branch.

-marginal branch (left and right).

Drainage of veins through the Coronary sinus (a

vascular sinus which is a thin-walled sinus with no

smooth muscles) which drains the blood to the

right atrium.

(Note: that these arteries or this system of arteries

oS.vascularity of the heartreferred to as theis

thatswhy we explained them to get the idea about

how ischemia occurs).

Normal coronary blood flow:

The resting coronary blood flow= 225ml/min

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(Relaxed situation e.g: sleeping)

In strenuous exercise = increase three to

four folds.

(Sometimes up to 7 folds)

Now the question is, when does perfusion

occur? during the systole or the diastole?

Systolic pressure is created from the

contraction of the left ventricle (phase of

contraction).

Diastolic pressure is created from the

recoil of the aorta (phase of relaxation).

During systole: arteries (the

subendocardial arteries) of the heart willofperfusionso most of thebe compressed

.diastoleoccurs duringheart

As you see in the following diagram:

Systole BF is 100 ml/minute.

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Diastole BF is 300 ml/minute.

What controls the coronary blood flow and all

arteries of the body in general?

The need or the increased demand that increases

the blood supply.

if there's imbalance between the supplyOtherwise (

ae demand) it's going to be consideredand th

Ischemia.which is called(defect )disorder

Blood flow is controlled mainly by:-

Metabolic (activities) regulation: if it is increased then

the BF will increase. (Blood flow through the coronary

system is regulated almost entirely by local arterial

vasodilatation in response to cardiac muscles' needfor nutrients which leads to increased contraction so

there will be an Increase in the rate of coronary

blood flow).

Nervous regulation: sympathetic stimulationincreases the heart rate and contractility, so it will

increase the cardiac output which means increased

coronary blood flow.

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Now let us start with pathophysiology:-

:Ischemia

There are two important subjects placed

under or related to ischemia generally:

-Ischemia.

-Necrosis.

Now what do we mean by Ischemia?

It's the lack of oxygen due to inadequate perfusion

of the myocardium, which causes imbalance

between oxygen supply and demand.

Specifically: when there's a constriction, a

narrowing or a subdivision (partial occlusion) in

the arteries which supply the heart (coronary

arteries).

The other part is necrosis (myocardial infarction):

When there's complete occlusion of the blood

vessel (not partial).

Then the myocytes beyond the occlusion will die

and it might be fatal (this leads to a state of

necrosis).

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Ischemia equation :

e.g u need 10 liters, and

blood supplies only 8 liters (this leads to ischemia).

-Causes of myocardial ischemia:

The most common cause is Coronary atherosclerosis

(This means blockage of arteries):

Thickening or narrowing of the wall of the arteries

due to accumulation of fatty materials such as

cholesterol (most common in old people).

Epicardial coronary arteries are the major site.

Major risk factors that cause atherosclerosis

(precipitating factors):

Increase in LDL (low density lipoprotein). Decrease in HDL (high density lipoprotein). Cigarette smoking. Hypertension. DM (Diabetes mellitus).

*Additional note: low density lipoprotein means bad cholesterol and HDL means good

cholesterol.

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We all know that smoking, hypertension, etc are

common causes, but what is the mechanism?

Because all these things lead to destruction or injury tothe endothelial (has to be smooth) layer of the arteries

which leads to aggregation of clotting factors (platelets)

due to the fragility of its surface (no luminar flow).

This mechanism is similar to getting injured or having an

external cut, this leads to rough (fragile) surface and

aggregation of clotting factors.*remember that a blood vessel consists of 3 layers: tunica interna (endothelial), tunica

media, tunica externa.

*there are 2 type of blood flow: luminar flow (steady or smooth state) and turbulent

flow.

Normal function of vascular endothelium:-Local control of vascular tone.

-Maintenance of an anticoagulant surface.-Defense against inflammatory cells.Loss of these defensesleads to:-Inappropriate constriction.

-Luminal clot formation.-Abnormal interactions with blood monocytes &

platelets.

- Now the occlusion is caused either by Thrombosis or

Embolism, but what the difference?

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The Location of the obstruction Influences the quantity

of myocardial ischemia, Determines the severity of the

clinical manifestations which means that if the occlusion

was in a major artery then the effect will be major (the

heart will be affected so much, massive destruction of

cells leads to massive dead myocytes) but if the artery is

small the complication will be less (why? Because there

are fewer amounts of dead cells).Collateral circulation:

Before that there's a question: If a young man had a

myocardial infarction he would die but an old or a

middle- aged man wouldn't?

Due to the collateral circulation that is only formed

in old people and athletes.

Which means that an area (the same one) supplied

by many arteries (network of blood vessels), it is

not opened in young people (except athletes) but

opens when we get older.

*in athletes because they have a high demand

(cardiomegaly).

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If heart rate is less than 60 it's a disorder which is

called brady cardi but in athletes it's not (their heart

size is larger = cardiomegaly) normal to have HR

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3) Cell membrane function:

-Leakage of potassium and uptake of sodium by

myocytes.4) Electrical function:-ECG changes:Repolarization abnormalities.Transient ST segment depression.

-Electrical instability:Ventricular tachycardia and fibrillation.

Later on when we discuss arrhythmia we will know

that one of its important causes is ischemia and

massive myocardial infarction (it may lead toventricular fibrillation which is fatal).

-angina

There are 2 types:

-unstable angina:

which is misdiagnosed betweenunstable angina and acute MI (myocardial infarction)

both of them are Acute coronary syndromes (symptoms:

retrosternal severe chest pain near to the left hand).

We can differentiate between them by ECG, we have to

do blood tests, ckmp, troponine (will be +ve for MI

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patients andve for unstable angina patients) next lecture

we will discuss it in details.

-Stable angina: chronic artery disease.Characteristics:Heaviness, Pressure, Squeezing,Smothering and choking pain.

Causes:

-CAD (coronary artery disease).- Aortic valve disease.

- Hypertrophic cardiomyopathy.

History:

A man > 50 years.

A woman > 60 years.

Pain with physical & emotional exertion.

Lasts to 5-10 min (relieved by vasodilators).

But how does the pain occur or start? Radiating pain to the left

shoulder, both arms, back, interscapular region, root of the neck,

jaw and teeth. but you need to know any other symptoms that

are not related to the heart in diagnosing angina or MI

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(e.g abdominal pain) otherwise, you might kill the patient

because you will forget or misdiagnose that he has angina and

you will give him another treatment for another disease (that

you had in mind).

Both types have the same cause (narrowing and

constriction of the coronary artery) but the stable is

relieved by Vasodilators (nitro-peceline sublingual,

nitrates, -adrenergic blockers, Calcium, antagonists and

Antiplatelet drugs). Occurs mainly after doing exercises

especially when the demand becomes more than thesupply, which leads to a severe chest pain but signs and

symptoms will be subsided by Vasodilators. But in

unstable pain will not be subsided by Vasodilators.

*tread-mill or stress test: to know if your heart is doing well (220- the

age) e.g ( your age is 20 then 220-20=200 this means that your HR after

doing exercises should reach 200 without feeling any chest pain

otherwise there would be a disorder).

Why are these patients given analgesics (morphine or opium) or

as we call them painkillers?

Because the heart pain is very severe (painful).

THE END