CORONARY ARTERY DISEASESE

THE CORONARY CIRCULATION


It has been estimated that over one third of the population eventually will die of CAD, and 20% will develop symptoms when younger than age 60 years.

ANATOMY OF THE CORONARY ARTERIES


The first branches of the aorta are the right and left coro¬nary arteries and arise from the sinuses of Valsalva. The right coronary artery It gives
• the sinus node artery
• right marginal artery
• posterior descending artery and, by an extension to the crux, branches into an atrioventricular node artery and several terminal posterolateral left ventricular branches(PLVs).
The left main coronary artery arises from the left posterior coronary sinus and averages 2 cm in length, although this may vary from 1 mm to 4 cm. it bifurcates into the left anterior descending (LAD) and left circumflex coronary arteries. In many instances, rather than bifurcating, a trifurcation occurs when the ramus medianus vessel originates between the anterior descending and the circumflex arteries.





NORMAL PHYSIOLOGY


Normal coronary blood flow approximates 0.7 to 0.9 ml. per gm (averages 225ml/min.). of myocardium per minute and delivers 0.1 ml. of oxygen per gm. per minute to the heart; The extraction of oxygen in the coronary bed is high, averaging 75% under normal conditions and increasing to nearly 100% during stress. Coronary artery blood flow occurs primarily during diastole because systolic myocardial con¬traction increases intramyocardial vascular resistance.

Factors influencing coronary vascular resistance

? metabolic
Factors that increase coronary vascular resistance
? ?- sympathetic receptors
? Myogenic mechanism
Factors that decrease coronary vascular resistance
? ?- sympathetic receptors
? Myogenic mechanism
? CO2
? Decreased O2 tension
? Hydrogen ions
? Lactate
? Potassium ions
? Adenosin
? physical
? Systolic compression
? Aortic pressure: the coronary vasculature can compensate and maintain normal coronary perfusion pressure between systolic pressure of 60 and 180 mm Hg via the process of autoregulation.
? Neural and hormonal
? ?- sympathetic receptors are more prominent in the epicardial vessels, and the ?- sympathetic receptors are more prominent in the intramuscular vessels.
? parasympathetic stimulation has only a slight vasodilatory effect.
-1-