Coronary Circulation Flashcards
Coronary Arteries
-Right Coronary artery-major branch acute marginal
-Left Main Coronary travels 1-1.5 cm before branches into
1- Left Anterior Descending (LAD) follows the anterior interventricular groove; major branches: diagonal branches distributing over the free wall of the left ventricle, and septal branches pentrating into the anterior portion of the ventricular septum
2- Circumflex artery (LCX)- follows the left atrioventricular groove posteriorly; major branche: obtuse marginals
3- Ramus Intermedians: it is not unusual for there to be a third branch from the LMT between the LAD and LCX
Cardiac veins
- venous drainage of the myocardium is predominately to the right atrium via the coronary sinus
- the orifice of the coronary sinus has a diameter of 0.5-1 cm and opens into the RA near the inferior vena cava and ticuspid valve
- the 1.5-6.5 cm long coronary sinus rests in the posterior atrioventricular groove and receives venous blood from the left ventricle through the middle cardiac vein, posterior interventricular vein, greater cardiac vein and anterior interventricular vein
- the coronary sinus also receives blood from right ventricle through the small cardiac vein
- venous blood from the right ventricle returns to the RA through the anterior cardiac veins which empty directly and individually into the RA
Thebesian Vessels
- there are vessels connecting cardiac chambers to arterioles, capillaries and venules
- the coronary flow may return to the heart chambers through the typical route (artery- arteriole- capillary- venule- vein- right atrium) and it may drain directly from Arterioles, capillaries and venules into the cardiac chambers
- the right atrium receives the majority of the thesbesian drainage but the left and right ventricles do receive some thebesian drainage
Interconnections
- there is a minor amount of interconnectivity between coronary vessels including: arterial to venous shunts, arterial to arterial connections, venous to venous connections
- the circulation is a loop which force perfusion into territories whose primary route of delivery has been compromised
- sometimes during surgery requiring elective cardiac arrest, cardiologic solution is sometimes administered into the coronary arteries and the coronary sinus simulataneously without any apparent harm to the heart
Normal anatomical variant
- coronary dominants, LCX left circumflex artery, connected to RCA
- all three major arteries have the same ostia in the aortic root
- each major coronary artery has its own ostia in the aortic root
Distribution of blood flow
- coronary perfusion territories- coronary dominance
- redundancy of blood distribution to papillary muscle
- interdigitated borders
Coronary Dominance
- the posterior descending artery (PDA) travels in the posterior interventricular groove to the apex of the heart
- 70% PDA supplied by the RCA (right dominance)
- 20% PDA supplied by both the RCA and the left circumflex artery (co-dominant)
- 10% PDA supplied by the left circumflex artery (left dominant)
Papillary muscle blood flow
- the leaflets of the mitral valve are tethered to the anterior and posterior papilary muscles in the left ventricle
- failure of the papilary muscles results in acute mitral regurgitation and pulmonary edema
- the coronary circulation protects against papilary muscle failure resulting from ischemic heart disease by supply each papilary muscle from two different coronary arteries
- the posterior papillary muscle is supplied from the RCA and LCX arteries
- the anterior papillary muscle is supplied from the LAD and the LCX arteries
Borders of perfusion territories
-at all points of filling the territory has irregularly shaped borders with peninsulas of perfused tissue penetrating deeply into areas of unperfused tissue
Coronary perfusion occurs during diastole
- during diastole, aortic diastolic pressure is transmitted without resistance to the coronary ostia
- aortic arch and coronary sinuses act as minature reservoir, facilitating maintenance of uniform coronary inflow through diastole
- the epicardiac coronary arteries act as conductance or conduit vessels: 0.3- 5 mm diameter, no appreciable resistance to blood flow with no detectable pressure drop along the length of epicardial arteries
- the arterioles are 10-200 microns diameter- act as resistance vessels, large pressure drop
- in the right coronary arterty the flow is even in diastole and systole
- maximum flow occurs in LCA during diastole
Coronary flow during cardiac cycle
- flow occurs in the arteries supplying the subendocardial portion of the left ventricle only during diastole as pressure inside the LV is slightly higher than aorta during systole
- flow in the right ventricle and atria is not appreciably reduced during systole, because aortic pressure is much higher
- because diastole is shorter when the heart rate is high, left ventricular coronary flow is reduced during tachycardia
- because no blood flow in systole in the subendocardial portion of left ventricle, the region is prone to ischemic damage and is common site of MI
Coronary vascular resistance
- epicardial conduit artery resistance: insignificant is normal, in presence of >50% stenosis, this starts contributing to total coronary resistance and may reduce resting flow with >90% stenosis
- arterioles and resistance arteries: dynamic resistance from metabolic and autoregulatory adjustments to flow, changes in response to physical forces and metabolic needs of tissue
- compressive resistance- varies with time through cardiac cycle, related to cardiac contraction and systolic pressure, higher in subendocardial than subepicardial layers
Normal blood flow
- because no blood flow occurs during systole in the subendocardial portion of the left ventricle, this region is prone to ischemic damage and is most common site of myocardial infarction
- blood flow to the left ventricle is decreased in patients with stenotic aortic valves because the pressure in the left ventricle must be much higher than that in the aorta to eject the blood-vessels are severely compressed during systole
- coronary flow is also decreased when the aortic diastolic pressure is low-the rise in venous pressure in conditions such as congestive heart failure reduces coronary flow because it decreases effective coronary perfusion pressure
Myocardial oxygen consumption
- the myocardium extracts nearly all of the oxygen delivered to it from coronary blood flow
- normal venous oxygen saturation of coronary sinus is 30%
- any increase in oxygen consumption requires an increase in blood flow
- the driving pressure through the coronary vessel
- extravascular compression of the coronary arteries by heart contraction and
- the resistance of the coronary vessels
Autoregulation of coronary flow
- the intrinsic ability of the heart to maintain a constant blood flow over a wide range of coronary perfusion pressures
- basal blood flow remains fairly constant despite fluctuations in coronary artery pressure
- given that the myocardium extracts 70% of the oxygen supplied to it at rest, increases in MVO2 increases necessitate an increase in blood flow