Term
| What are 2 anatomical ways to determine dominant circulation in the heart? |
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Definition
1) Which side (right coronary or left circumflex) gives rise to posterior descending artery (90% are right dominant)
2) Which side gives rise to the AV nodal branch |
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Term
| Explain the anatomical course of the right coronary artery. |
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Definition
1) Comes off of base of aorta and winds around to the back of the heart in the coronary sulcus.
2) Gives rise to marginal artery first
3) Gives rise to the PDA in the posterior IV groove |
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Term
| Explain the anatomical course of the left coronary artery? |
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Definition
1) Exits the left base of the aorta and runs under the pulmonary trunk
2) Gives off LAD, which runs in the anterior IV groove
3) Continues as circumflex artery and winds around to the back of the heart (giving off left marginal branch as well) |
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Term
| Why does coronary artery disease present later in woman than in men? |
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Definition
Estrogen!
Until menopause, estrogen keeps HDL levels high (in men, the LDL accumulation contributes to atherosclerosis). |
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Term
True or False:
The initial presentation of CAD tends to be very serious. |
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Definition
True!
45% MI and 11% sudden death! |
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Term
| How is oxygen consumption determined? |
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Definition
O2 delivered= (carrying capacity/Hb amount)(saturation)(blood flow)
O2 consumption= (O2 delivery)(extraction), where extraction is the Arteriovenous oxygen difference. |
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Term
| How do you determine total body oxygen extraction? |
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Definition
| Systemic arterial O2 concentration- O2 concentration in blood returning to pulmonary artery. |
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Term
Explain why the heart has little ability to increase its oxygen consumption through oxygen extraction.
How can the heart ramp up oxygen delivery to itself? |
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Definition
1) Venous drainage of coronary circulation is only about 30% saturated (vs. 70% for the rest of the body).
2) O2 consumption= (O2 delivery)(extraction) and O2 deliver= (Hb amount)(Saturation)(Perfusion).
All you can do is increase PERFUSION (this is why coronary blood flow is SO IMPORTANT) |
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Term
| What are the 4 primary determinants of Myocardial Oxygen demand? |
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Definition
1) HR (greatest)
2) Contractility
3) LV Systolic BP (after-load)- aortic stenosis or HTN
4) LV volume/radius (LaPlace- pre-load)- aortic/mitral regurgitation
3>4 |
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Term
| Why might giving an inotropic drug for CHF decrease myocardial oxygen consumption? |
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Definition
Usually increasing contractility increases O2 consumption.
In case of CHF, HR, BP and LV volume are all increased already, and O2 consumption is high.
When you increase the contractility and the CHF resolves, HR, BP and LV volume may all decrease MORE than the relative increase, thereby decreasing O2 consumption overall. |
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Term
Why is aortic diastolic pressure the driving force behind coronary perfusion of the left ventricle?
Why is this not the case for the right ventricle? |
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Definition
1) Coronary perfusion pressure= Aortic pressure- Coronary sinus (venous) pressure
- LV systolic pressure is the same as aortic systolic pressure, so there is no P gradient in systole (no blood gets past myocardial wall, to endocardium, because of R3 resistance).
- In diastole, LV Pressure < Aortic Pressure, so blood can flow through coronary arteries to feed the left ventricle.
2) There is a pressure gradient in the RV in systole and diastole (RV systolic pressure < systemic arterial pressure) |
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Term
| How do the 3 levels of resistance to coronary perfusion pressure and how do they determine blood delivery? |
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Definition
R1
R1= Epicardial coronary arteries (larger myocardial vessels as well)
R2= Small arteries and pre-capillary arterioles
R3= Arteries penetrating myocardium to the endocardium
** To limit R3 component effect in subendocardium, R2 vessels there dilate, to keep R2 + R3 constant and to maintain perfusion** |
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Term
| How does the unevenness of R3 component of perfusion resistance influence coronary blood flow? |
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Definition
1) R3 is lower in epicardial regions, and therefore fills during systole (Endocardium does not get perfused until diastole)
2) In diastole, these filled vessels can then perfuse distally |
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Term
| Where does the greatest drop in coronary blood flow occur (i.e. in which types of vessels)? |
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Definition
| In the R2 resistance vessels (small arteries and pre-capillary arterioles), where resistance increases most dramatically. |
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Term
| At rest, how is coronary blood flow maintained at a constant level through a wide range of coronary perfusion pressures? |
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Definition
| Autoregulation of resistance in R2 vessels |
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Term
| Why does diastolic BP not increase much during exercise? |
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Definition
1) Coronary perfusion occurs in diastole, so increasing coronary blood flow during exercise is not due to increasing perfusion pressure.
2) R2 vessels vasodilate (decreasing resistance) to decrease resistance by 4X
**increased HR, limits diastolic filling time, however, so overall increase in coronary BF is about 2-2.5X** |
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Term
| How does coronary BF "reserve" differ from "peak" coronary BF |
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Definition
1) CBF reserve is (peak BF with maximal dilation) - (resting BF)
** Both directly related to coronary perfusion pressure** |
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Term
| In Atherosclerotic coronary artery disease, why do R2 vessels have to dilate so much? |
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Definition
First it compensates for R1, then R3 is subendocardium!
1) The disease primarily effects R1 vessels (luminal narrowing and increased resistance)
- R2 vessels dilate to compensate for this increased resistance.
2) Earliest disease manifestation is Diastolic Dysfunction (shift of EDPVR to left). With increased LV EDP, increasing the R3 component in the subendocardial region.
- R2 has to dilate EVEN further |
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Term
| Why does ischemia occur in coronary stenosis? |
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Definition
If R2 vessels reach their dilatory limits, ischemia occurs because of supply/demand mismatch, and LV EDP and EDV increase.
**Ischemic threshold in supply/demand curve indicates maximum vasodilation and indicates severity of obstructive disease ** |
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Term
What is the current gold standard for assessing the severity of coronary artery disease?
What are the issues with this standard? |
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Definition
1) % coronary stenosis measured by coronary angiography.
- >50% stenosis is critical level where perfusion drops off
- After this flow drops off exponentially to changes in stenotic pressure (critical zone)
2)
- Reproducibility (subjective readers)
- Significance of disease (segmental vs. diffuse disease/ "what is the point of normal comparison"?)
** UNDERESTIMATION of blood flow is major issue, and luminal cross-sectional area is better measure** |
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Term
| What is the impact of length of stenosis on BF at a given % stenosis? |
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Definition
| Flow decreases sharply with increased length of stenosis |
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Term
| What is the best predictor of peak coronary flow? |
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Definition
Cross-sectional luminal area
% stenosis does not matter as much as amount of lumen remaining!** |
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Term
| What area of the myocardium is at the greatest risk of ischemia and why? |
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Definition
Subendocardium
1) Greatest oxygen demand (requires most BF)
2) Greatest R3 component (only gets BF in diastole)
**It needs more and gets less, so RATE must be greater**
- Achieved by more vessels per unit area and larger size of vascular beds! |
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Term
| How is the rate of blood flow increased to the endocardium? |
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Definition
Remember, it needs the most (highest demand), but gets the least (R3 the greatest, only BF in diastole).
1) Achieved by more vessels per unit area
2) Larger size of vascular beds!
3) R2 vessel dilation in endocardium (using some of dilatory reserves, making vulnerable to ischemia) |
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Term
True or False:
At rest, subendocardial blood flow is less than epicardial blood flow |
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Definition
False!
It is initially greater (more vessels per unit area and larger vascular beds).
It decreases with increased HR and with CAD.
**Peak HR is limited by ischemia** |
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Term
| Why are functional tests of coronary blood flow performed under conditions that increase blood flow above resting levels? |
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Definition
Flow can be normal even through the most obstructed vessels at rest, because of auto regulation and collateral circulation.
Gotta Stress-em out (In maximal exercise, BF is 2.5X) |
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Term
| What does the "ischemic" threshold have to do with coronary supply/demand? |
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Definition
It is the point at which supply for a given demand drops from the normal curve.
The more severe the ischemic disease, the lower the threshold |
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Term
| What pharmacological methods are available to raise coronary circulation in patients that cannot perform exercise for diagnostic testing? |
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Definition
** Adenosine and Dipyridamole are agents of choice, except in case of asthma (risk of bronchospasm), when Dobutamine is used**
1) Vasodilator (Adenosine)
- dipyridamole slows adenosine metabolism
- Ragedenson is adenosine 2A agonist
2) Inotropic (Dobutamine) to increase HR, BP and contractility |
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Term
| What does an ischemic response look like on exercise EKG? How does it predict outcome? |
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Definition
1) ST depression (> 1mm), 80 ms after J point indicates ischemia and probably CAD (worse if down-sloping with chest pain and/or decreased peak HR)
2) Predictive of mortality risk
- down-sloping is greater prognostic indicator
- with chest-pain increases predictive power (worse prognosis)
- lower peak heart rate (worse prognosis)
** increasing post-test probability (by bayes theorem) |
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Term
| What is the single best predictor of risk associated with a stress test? |
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Definition
Abnormal functional capacity
**related to slower heart rate recovery**
Others
- Chronotropic incompetence
- Chest pain
- Decreased peak HR |
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Term
| What are the 4 determinants of sensitivity and specificity of exercise testing? |
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Definition
1) Sensitivity (68%)
- Treatment of equivocal test results
- Comparison with better test
- Exclusion of patients on digitalis
- Publication year
2) Specificity (77%)
- Treatment of up-sloping ST segment depression
- Exclusion of patients with prior MI or LBBB
- Use of pre-excercise hyperventilation tracing |
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Term
| Why is the exercise test of high utility to patients with Atypical chest pain but NOT Typical Angina? |
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Definition
| Atypical chest pain has intermediate pre-test probability (50%), while typical angina has high (90%) pre-test probability |
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Term
True or False:
Cardiac Scintigraphy is more sensitive AND more specific than exercise testing. |
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Definition
True
**Flow heterogeneity is early indicator of ischemic disease. |
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Term
What does a perfusion abnormality that is present both at rest as well as after exercise indicate when found by planar perfusion imaging?
What if it is seen in the posterior wall? |
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Definition
Prior MI (intensity of defect indicates severity of MI)
** If it was only during exercise, it would be CAD**
This is the right CA distribution, perhaps the PDA. |
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Term
| Why is SPECT imaging preferred to planar perfusion imaging? |
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Definition
| Increases sensitivity without change in specificity |
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Term
True or False:
SPECT imaging can be used to distinguish between high-risk and low-risk groups of patients for Cardiac death or MI |
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Definition
True, even BETTER than exercise testing
**critical to determine benefit of coronary angiography vs. medical management** This save money and needless procedures. |
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Term
| What did the COURAGE trial tell us about the utility of stenting in patients with CAD who are receiving aggressive medical therapy. |
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Definition
| There is no difference, so revascularization therapy needs prior SPECT testing to identify those at risk! |
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