CORONARY CIRCULATION

Dr.Mohammed Sharique Ahmed QuadriAssistant professorAl Maarefa College

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Objectives

• Review the functional anatomy of coronary circulation

• Recognize the importance of phasic changes in coronary blood flow

• Describe the factors affecting the coronary blood flow

• Recognize the clinical significance (IHD)

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Coronary Artery & their Branches

Coronary arteries arises from the base of the aorta

• LCA– Left Anterior Descending (LAD)– Marginal Artery– Circumflex Artery

• RCA– Marginal Artery– Posterior descending Branch

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Coronary Arteries

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Venous return• Most venous return is through1)Ant cardiac veins & 2)coronary sinus into

Right Atrium

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CORONARY BLOOD FLOW

• Coronary blood flow in Humans at rest is about 225-250 ml/minute, about 5% of cardiac output.

• At rest, the heart extracts 60-70% of oxygen from each unit of blood delivered to heart [other tissue extract only 25% of O2.

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CORONARY BLOOD FLOWWhy heart is extracting 60-70% of O2?

• Because heart muscle has more mitochondria, up to 40% of cell is occupied by mitochondria, which generate energy for contraction by aerobic metabolism, therefore, heart needs more O2 supply.

• When more oxygen is needed e.g. exercise, O2 delivery can be increased to heart only by increasing blood flow.

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Blood flow to Heart during Systole & Blood flow to Heart during Systole & DiastoleDiastole

Blood flow to heart muscle reduces during Blood flow to heart muscle reduces during systole because of two reasons systole because of two reasons

• During systole when heart muscle contracts (specially in powerful left ventricle) compresses the coronary arteries therefore blood flow is less to the left ventricle during systole and more during diastole.

• Second , the open aortic valve partially blocks the entrance to coronary vessels

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Phasic changes in coronary bld flowEffect of cardiac muscle contraction

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• Coronary blood flow to the right side is not much affected during systole.

Reason---Pressure difference between aorta and right ventricle is greater during systole than during diastole, therefore more blood flow to right ventricle occurs during systole.

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Effect of pressure gradient of aorta &diff chambers of heart

pressure(mm hg) in Pressure diffrential (mmhg)Between aorta &

Aorta Left ventricle

Rt ventricle

Lt ventricle Rt ventricle

Systole 120 121 25 -1 95

diastole 80 0 0 80 80

• As in systole pressure in left ventricle is slightly higher than in aorta blood flow reduces

• On the other hand press diff in aorta & rt ventricle & aorta & rt atrium is more during systole than diastole, coronary bld flow is not appreciably reduce during systole

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• CORONARY BLOOD FLOW DURING SYSTOLE AND DIASTOLE

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• During systole blood flow to subendocardial surface of left ventricle is almost not there,

–therefore,• this region is prone to ischemic damage

and most common site of Myocardial infarction.

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• Effect of Tachycardia on coronary blood flow:

During increased heart rate, period of diastole is shorter therefore coronary blood flow is reduced to heart during tachycardia.

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• FACTORS AFFECTING BLOOD FLOW TO CORONARY ARTERIES

-Pressure in aorta -Chemical factors -Neural factors

NOTE—Coronary blood flow shows considerable Autoregulation.

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• CAUSES OF DECREASED BLOOD FLOW TO LEFT VENTRICLE

1-Aortic stenosisReason---As left ventricle pressure

is very high during systole, therefore, it compresses the coronary arteries more.

2-When diastolic pressure in aorta is low, coronary blood flow is decreased

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Chemical factors affecting Coronary blood flow

Chemical factors causing Coronary vasodilatation (Increased coronary blood flow)-Lack of oxygen-Increased local concentration of Co2-Increased local concentration of H+ ion-Increased local concentration of k + ion-Increased local concentration of Lactate,

Prostaglandin, Adenosine, Adenine nucleotides.

NOTE – Adenosine, which is formed from ATP during cardiac metabolic activity, causes coronary vasodilatation.

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Neural factors affecting Coronary Blood Flow1. -Effect of Sympathetic stimulation2. -Effect of Parasympathetic stimulation

Sympathetic stimulationBy stimulation of Alpha Adrenergic receptors

mediate vasoconstrictionBy stimulation of Beta Adrenergic receptors

mediate vasodilatation

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Sympathetic stimulation------Cont Effect of sympathetic stimulation in intact

body:---Epinephrine and Norepinephrine causes VASODILATATION.

HOW ? But the Direct effect of sympathetic on

Coronary arteries is VASOCOSTRICTION.WHY ?

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Indirect effect of sympathetic stimulation

• Stimulation of sympethetic nerves release of nor epinephrine

increase of H.R &force of contraction(effect mediated by β1-receptors)

Release of vasodilator metabolites

vasodilatation20

Direct effect of sympathetic stimulation

• When the ionotropic &chronotropic effect of noradrenergic discharge are blocked by Beta adrenergic receptor blocking drugs, injection of norepinephrine or stimulation of noradrenergic nerves in un anaesthetized animal elicits coronary vasoconstriction.

• Thus direct effect of noradrenergic stimulation is V.C

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Benefits of indirect effect of noradrenergic discharge

• When systemic B.P decreases very low as in shock reflex increase of noradrenergic discharge

Increase coronary blood flow sec to metabolic changes in myocardium

In this way circulation of heart is preserved while

flow to other organs compromised

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• Effect of Parasympathetic stimulation – -Parasympathetic influences are minor and weakly

vasodilatory.

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Special features of cardiac muscle metabolism

• Heart uses primarily free fatty acids and to lesser extent glucose and lactate for metabolism.

in ischemic / anaerobic conditions

Derives energy from Anaerobic glycolysis

Forms lactic acid (one of cause of cardiac pain )

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CORONARY ARTERY HEART DISEASE

• ISCHEMIC HEART DISEASE (IHD) (ANGINA PECTORIS)

• MYOCARDIAL INFARCTION

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RISK FACTORES OF IHD:

– CIGARETTE SMOKING– HYPERTENSION– DIABETES MELLITUS– INCREASED LIPIDS ( CHOLESTROL)– OTHER FACTORS: LACK OF EXERCISE,

ANXIETY etc.

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IHD(ANGINA PECTORIS):– THERE IS REDUCED CORONARY ARTERY BLOOD

FLOW DUE TO ATHEROSCLEROSIS (CHOLESTROL DEPOSITION SUBENDOTHELIAL -- Plaque)

PATIENT COMPLAINS OF TIGHTNESS OR PAIN IN THE MIDDLE OF CHEST (RETROSTERNAL) FOR FEW MINUTES. PAIN OFTEN RADIATES TO INNER SIDE OF LEFT ARM.

PAIN IS PRECIPETED BY EFFORT AND RELIEVED BY REST.

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MYOCARDIAL INFARCTION (MI):

– IT IS DUE TO OBSTRUCTION TO THE CORONARY BLOOD FLOW, ATLEAST 75 % OF LUMEN OF CORONARY ARTERY IS BLOCKED BY THROMBUS.

– MI IS THE COMMON CAUSE OF DEATH.

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Applied Aspect

THE C A D.

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Electrocardiographic changes duringexercise test. Upper trace – significant horizontal ST

segment depression during exercise.

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INVESTIGATIONS:ECGCARDIAC ENZYMES e.g. CK, LDH, TROPONIN etc.ECHOCARDIOGRAPHYTREADMILL EXERCISE TESTTHALLIUM STRESS TESTCORONARY ANGIOGRAPHY

NOTE: ○ ECG CHANGES IN IHD:

ST DEPRESSION OCCURS IN ECG IN RESPECTIVE LEADS○ ECG CHANGES IN MI:

ST ELEVATION OCCURS IN ECG IN RESPECTIVE LEADS

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TREATMENT:– CORONARY DILATORS E.g. NITRATES– BETA-BLOCKERS– ANGIOPLASTY (DILATE AREA OF CONSTRICTION)– STENT– BYPASS SURGERY

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Percutaneous transluminal coronary angioplasty (PTCA). (a) Coronary angiography demonstrates a severe stenosis in the proximal left anterior descending artery. (b)

During PTCA a soft guidewire is passed across the stenosis and then a balloon is expanded that dilates the stenosis. (c) Post-PTC

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An intracoronary stent.

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CORONARY ARTERY BYPASS SURGERY

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Thanks

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