Lecture – 8 DR ZAHOOR ALI SHAIKH CORONARY CIRCULATION Lecture – 8 DR ZAHOOR ALI SHAIKH

CORONARY CIRCULATION Heart is supplied by TWO CORONARY arteries: 1- Right coronary artery---(RCA) 2- Left coronary artery---(LCA) These coronary arteries arise at the root of the aorta.

Coronary artery & their branches LCA---- -Lt Anterior Descending (LAD) -Marginal Artery -Circumflex Artery RCA ---- -Marginal Artery -Posterior descending branch

Left coronary artery (LCA) –Divides in Anterior Descending (LAD) Circumflex artery LAD--- Supplies anterior and apical parts of heart ,and Anterior 2/3rd of interventricular septum. Circumflex branch-- supplies the lateral and posterior surface of heart.

Right coronary artery(RCA) supplies: Right ventricle Part of interventricular septum (posterior 1/3rd) Inferior part of left ventricle AV Node

Diagram of coronary circulation

Venous return of Heart Most of the venous blood return to heart occurs through the coronary sinus and anterior cardiac veins, which drain into the right atrium

Blood flow to Heart during Systole & Diastole During systole when heart muscle contracts it compresses the coronary arteries therefore blood flow is less to the left ventricle during systole and more during diastole. To the subendocardial portion of Left ventricle it occurs only during diastole

As we know blood flow to subendocardial surface of left ventricle during systole is not there, therefore, this region is prone to ischemic damage and most common site of Myocardial infarction.

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.

CORONARY BLOOD FLOW DURING SYSTOLE AND DIASTOLE

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.

Other causes of decreased blood flow to left ventricle 1-Aortic stenosis Reason---As left ventricle pressure is very high during systole, therefore, it compresses the coronary arteries more. 2-When aortic diastolic pressure is low, coronary blood flow is decreased

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.

CORONARY BLOOD FLOW Why 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 O2. When more oxygen is needed e.g. exercise, O2 can be increased to heart only by increasing blood flow.

Factors Affecting Blood Flow to CORONARY ARTERIES -Pressure in aorta -Chemical factors -Neural factors NOTE—Coronary blood flow shows considerable Autoregulation.

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.

Neural factors affecting Coronary Blood Flow -Effect of Sympathetic stimulation -Effect of Parasympathetic stimulation Sympathetic stimulation Coronary arteries have Alpha Adrenergic receptors which mediate vasoconstriction Beta Adrenergic receptors which mediate vasodilatation

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 ?

Effect of Parasympathetic stimulation -Vagus nerve stimulation (Parasympathetic) causes coronary vasodilatation

NEUTRIENT SUPPLY TO HEART Heart uses primarily free fatty acids and to lesser extent glucose and lactate for metabolism.

CORONARY ARTERY HEART DISEASE ISCHEMIC HEART DISEASE (IHD) (ANGINA PECTORIS) MYOCARDIAL INFARCTION ANGINA PECTORIS: THERE IS REDUCED CORONARY ARTERY BLOOD FLOW DUE TO ATHEROSCLEROSIS (CHOLESTROL DEPOSITION SUBENDOCARDIALLY -- Plaque)

CAUSES OF IHD: CIGARETTE SMOKING HYPERTENSION DIABETES MELLITUS INCREASED LIPIDS ( CHOLESTROL) OTHER FACTORS: LACK OF EXERCISE, ANXIETY etc.

IHD: IHD IS USED TO DESCRIBE DISCOMFORT IN THE CHEST DUE TO DECREASED CORONARY BLOOD FLOW (TRANSIENT MYOCARDIAL ISCHEMIA). 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.

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 COMMEN CAUSE OF DEATH.

Applied Aspect THE C A D.

Electrocardiographic changes during exercise test Electrocardiographic changes during exercise test. Upper trace – significant horizontal ST segment depression during exercise.

INVESTIGATIONS: ECG CARDIAC ENZYMES e.g. CK, LDH, TROPONIN etc. ECHOCARDIOGRAPHY TREADMILL EXERCISE TEST THALLIUM STRESS TEST CORONARY 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

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

Percutaneous transluminal coronary angioplasty (PTCA) 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

An intracoronary stent.

CORONARY ARTERY BYPASS SURGERY

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