Flashcards in Coronary Circulation Deck (61)
where do the 2 coronary arteries arise?
from the aortic sinuses behind the left and right coronary aortic valve cusps at the root of the aorta
what are the 2 major arteries and their major branches, and what they all follow??
1. right coronary
2. left main coronary travels 1-1.5 cm before branching
-left anterior descending (anterior interventricular artery) follows anterior interventricular groove to apex of heart
-circumflex artery (LCX) follows left atrioventricular groove posteriorly
-ramus intermedians (optional) between LAD and LCX
what are the major branches of the LAD?
1. diagonal branches distributing over free wall of left ventricle
2. septal branches penetrating into anterior portion of ventricular septum
what are the major branches of the LCX?
to where is myocardium drained?
venous drainage is mostly to right atrium via long coronary sinus
-opens into RA near IVC and tricuspid valve
-CS rests in posterior AV groove and gets venous blood from left ventricle through middle cardiac vein, posterior interventricular vein, great cardiac vein, anterior interventricular vein, and (from RV) small cardiac vein
how does venous blood from right ventricle return to the RA?
anterior cardiac veins empty directly and individually into the RA
-small cardiac veins enter coronary sinus, which enter RA
thebesian vessels and where they drain most
connect cardiac chambers to arterioles, capillaries, and venules
-coronary flow may return from typical route or via Thebesian vessels
-mostly drain into RA, but also LV and RV
what is the typical route of coronary flow?
artery --> arteriole --> capillary --> venule --> vein --> right atrium
normal anatomical heart variants
-all three major arteries have same ostia in aortic root
-each major coronary artery has its own ostia in the aortic root
typical blood distribution of coronary arteries (right dominant pattern)
LCX: free wall of LV between anterior and posterior papillary muscle
LAD: free wall of LV, anterior 2/3 of ventricular septum, and small part of free wall of RV
RCA: free wall of RV, posterior 1/3 of interventricular septum, and posterior wall of LV to posterior papillary muscle
there is significant overlap
coronary dominance of posterior descending artery
travels in posterior interventricular groove to apex of heart
-70% of PDAs are supplied by RCA (right dominance)
-20% are co-dominant
-10% are supplied by LCX (left dominant)
what are leaflets of mitral valve tethered to? what happens if they fail?
anterior and posterior papillary muscles in left ventricle
-failure causes acute mitral regurgitation and pulmonary edema
what are the anterior and posterior papillary muscles supplied from?
anterior: supplied by LAD and LCX arteries
posterior: supplied by RCA and LCX arteries
are the borders of cardiac perfusion territories irregular or regular?
they are very irregular and complex, b/c very interdigitated border
when does coronary perfusion happen?
it occurs during (early) diastole, b/c aortic diastolic pressure is transmitted w/o resistance to coronary ostia
-aortic arch and coronary sinuses act as a miniature reservoir to maintain uniform coronary inflow
-in RCA, force of external compression is much less from weaker RV, to keep even flow during diastole and systole
what is the major variable controlling blood flow?
change in coronary vascular resistance
what do epicardial coronary arteries act as?
-0.3 to 5 mm diameter
-no appreciable resistance to blood flow w/ no detectable pressure drop along length of epicardial arteries
what do arterioles act as?
-10-200 micron diameter with large pressure drops
--those less than 300 um account for 95% of resistance across coronary bed
--those less than 100 um account for 50% of total coronary resistance
is diastole longer or shorter when heart rate is high?
diastole is shorter when HR is high
-left ventricular coronary flow is reduced during tachycardia
when is the pressure differential between aorta and RV, and aorta and atria greater?
-thus, coronary flow here is not appreciably reduced during systole
where does no blood flow occur during systole? and what does this mean?
subendocardial part of left ventricle
-most prone to ischemic damage, so most common site of MI
3 components to resistance to coronary blood flow
R1 - epicardial conduit artery resistance (pathologic)
R2 - arterioles and resistance arteries (metabolic)
R3 - compressive resistance (mechanical)
epicardial conduit artery resistance
-if over 50% stenosis, it starts contributing to total coronary resistance, and may resting reduce flow with over 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 (mechanical) resistance
-varies with time through cardiac cycle
-related to cardiac contraction and systolic pressure
-higher in subendocardial than subepicardial layers
how is blood flow to LV affected in patients with stenotic aortic valves?
blood flow is decreased b/c pressure in LV must be much higher in the aorta to eject the blood
-vessels are severely compressed during systole
what happens to coronary flow when aortic diastolic pressure is low?
flow decreases b/c the rise in venous pressure decreases effective coronary perfusion pressure
myocardial O2 consumption
myocardium extracts nearly all of O2 delivered to it from coronary blood flow
-normal venous O2 saturation of coronary sinus is 30% (so myocardium extracts 70% of O2 supplied to it at rest)
-any increase in O2 consumption needs increase in blood flow
what is coronary blood flow determined by?
1. driving pressure through coronary vessel
2. extravascular compression of coronary arteries by heart contraction
3. resistance of coronary vessels