Coronary circulation Dr S Parthasarathy MD DA DNB

Coronary circulation Dr. S. Parthasarathy MD. , DA. , DNB, MD (Acu), Dip. Diab. DCA, Dip. Software statistics Ph. D (physio) Mahatma Gandhi medical college and research institute , puducherry – India

• The left main and right coronary arteries arise from the aorta behind the left and right aortic valve leaflets

Right Coronary Artery (RCA) • • • The right coronary artery branches into: Right marginal artery Posterior descending artery The right coronary artery supplies: Right atrium ● Part of the left atrium ● Right ventricle ● Posterior interventricular septum ● Sino-atrial node (in 60%) ● Atrioventricular node (in 80%)

• Circumflex artery • left anterior descending • Left posterior descending • Dominant ? ?

• • • The left coronary artery supplies: ● Left atrium ● Left ventricle ● Anterior interventricular septum ● Sino-atrial node (in 40%) ● Atrioventricular node (in 20%)

• • • Four veins lead into the coronary sinus: ● Great cardiac ● Middle cardiac Small cardiac Oblique

• Penetrate • epicardial plexus • Subendocardial plexus

Blood flow • The resting coronary blood flow in human being averages about 225 ml /min, which is about 4 to 5 percent of the total cardiac output. • Six to seven times CO increased yet the coronary blood flow is increased 3 – 4 times • 3 - 4 times is the Coronary reserve !!

Extraction high ? ? • The energy requirements of the myocardium are provided almost aerobically with little capacity for anaerobic metabolism. • During resting condition, 70 to 80 % of oxygen carried by coronary blood is extracted by the myocardium. • Extraction cant increase on stress but the cardiac output / coronary flow can increase

• Collateral channels are blood vessels (usually small) which allow blood to flow directly from one artery to another. • A coronary collateral circulation may also arise from different branches of the same coronary artery or from branches of two different coronary arteries

Collateral • Usually negligible because the driving pressure at the two ends of the anastomoses is nearly equal. • if the artery supplying one branch of this collateral circulation becomes occluded, the large pressure reduction will divert blood flow through the patent artery and into the distribution of the occluded artery through these collateral vessels.

Micro circulation • coronary microcirculation, formed by vessels with < 300 microns in diameter. • Rich network of capillaries • One / myocyte • But less in IV septum and AV node.

Micro circulation

Myocardial contrast echocardiography • technique capable of providing information on the anatomy and function of the microcirculation in vivo. It employs an intravascular tracers with rheologic properties similar to red blood cells. This tracers freely flows into the coronary microcirculation, without ever leaving the vascular compartment, and it is detectable by ultrasound procedures during its passage into the micro vessels.

Coronary circulation • Coronary blood flow is phasic, • In diastole

Phasic variations • More for subendocardial vessels • More for LV • • The relative maintenance of subendocardial blood flow may also be related to the extensive number of redundant arteriolar and capillary anastomoses in the subendocardium.

Phasic more for left coronary

Coronary circulation • Blood supply to the LV is directly dependent on the difference between the aortic pressure and LV end-diastolic pressure (coronary perfusion pressure) • inversely related to the vascular resistance to flow, • Two other determinants of coronary flow are vessel length and viscosity

Assumptions • The physiology of coronary blood flow is based upon the assumption that coronary arteries are non distensible tubes, and that blood is a homogeneous fluid.

CPP = DBP – LVEDP … What happens when ? ? • LVH – end diastolic pressure rise – CPP decrease • Tachycardia – diastole time decrease – flow decrease • Aortic regurgitation – diastolic pressure reduced - CPP decrease

CPP = DBP – LVEDP

Factors affecting circulation • The myocardial metabolism is aerobic, an • increased O 2 demand quickly has to lead to vasodilatation. • The following factors are involved in the coronary vasodilatation

REGULATION – metabolic factors • Oxygen is a mild vasoconstrictor • Hypoxia vasodilation AMP ---- MORE AMP – ADENOSINE • Hypoxia ATP • Accumulation of lactate and H+ ions • Prostacyclins

Neuro humoral factors: • Nor epinephrine released from sympathetic nerve endings and adrenal epinephrine have a vaso dilatory effect on the distal coronary vessels via beta 2 adrenoceptors.

Endothelial factors: • ATP (e. g. , from platelets), • bradykinin, histamine and acetylcholine are vasodilators. • They liberate nitric oxide (NO) from the endothelium, which diffuses into vascular muscle cells to stimulate vasodilatation

Endocardial viability ratio • EVR = DPTI / TTI = oxygen supply / demand • 1 or above is ok • 0. 7 – subendocardial ischemia

EVR

Steal • Coronary artery steal is an absolute decrease in collateral dependent myocardial perfusion at the expense of an increase in blood flow to a normally perfused area of myocardium, as may follow the drug-induced vasodilation of coronary arterioles. • Eg. Ischemia , collaterals , isoflurane

Normal – collateral - Steal

Summary • • Anatomy Extraction and flow Collateral Microcirculation Phasic flow Determinants EVR Steal

Thank you all • Is it clear or have you to Put fingers in the face and get confused ? ?