Quiz 9 Flashcards
major branches of the coronary arteries
RCA to PDA
Left Main to LAD, L Circ, Ramus (37%)
What is the Ramus Intermedius? In what percentage of the population does it exist?
37% of ppl have trifurcation of left main
Do the major epicardial arteries contribute significantly to coronary vascular resistance?
no, myocardial vessels do
What is capillary density? Is capillary density increased or decreased in the myocardium?
Increased
What are the major determinants of myocardial oxygen demand?
HR
Contractility
Systolic wall tension
What are the major determinants of myocardial oxygen supply?
Coronary blood flow
O2 carrying capacity
Is resting oxygen consumption of the heart high or low relative to other organs in the body?
Its the highest at 9.7 ml/100 g/min
What is the formula for coronary perfusion pressure?
Diastolic BP – LVEDP (or PCWP)
Is oxygen highly extracted from blood flowing through the heart?
yes, higher than any other organ
Does the majority of coronary blood flow occur during systole or diastole in the left ventricle? Why?
Diastole
Extravascular compression during systole markedly affects coronary flow
Which layer of the myocardium is at greatest risk for ischemia? Why?
subendocardium
Epicardial coronary stenoses are associated with reductions in the subendocardial to subepicardial flow ratio
What is coronary flow reserve? how much max vs resting?
Difference between resting/baseline blood flow and maximal flow
maximal flow is 4 – 5 times as great as at rest
Which of the following places a greater oxygen cost on the heart? Pressure work versus volume work.
Pressures work
increasing arterial pressure at a constant cardiac output harder on heart
How stenotic do coronary vessels have to be before there is a significant decrease in flow?
60% occluded or 40% max Radius
What is the final intracellular ion disturbance that leads to impaired myocardial contraction and cell death?
Intracellular Ca++ Overload
What are the effects of myocardial ischemia on systolic function?
Normal myocardium thickens and shortens during systole
minimal impairment to absence of movement (akinesis) to systolic lengthening and post- systolic shortening (dyskinesis)
May have compensation by surrounding areas of normal muscle
What are the effects of myocardial ischemia on diastolic dysfunction?
LVEDP rises
Impaired Relaxation
decreased compliance
The point After a brief episode severe ischemia, prolonged myocardial dysfunction with gradual return of contractile activity occurs
myocardial stunning
Presence of impaired resting LV function, owing to reduced CBF that can be restored toward normal by revascularization.
myocardial hibernation
What are some of the consequences of myocardial ischemia?
Myocardial Infarction Angina Death Systolic and diastolic dysfunction Ventricular Rupture or VSD Arrythmias CHF or Pulmonary Edema Cardiogenic Shock
What are some of the drugs used for the treatment of ischemia?
Antiplatelet/Anticoagulant Drugs Analgesics Beta-Blockers Oxygen Nitrates Calcium-Channel Blockers
What are some of the interventions used in the treatment of ischemia?
Coronary artery bypass surgery (CABG)
Percutaneous Coronary Interventions
- Coronary Balloon Angioplasty
- Bare-metal Coronary Stents
- Drug-eluting Stents
How long should you wait before doing elective surgery on a patient who has had a drug-eluting stent inserted?
> 6 months to 1 year
bare metal stent 90 days
What are some of the drugs that are used to reduce cardiac ischemic events during surgery?
- Volatile anesthetic agents may be preferred
- Anesthetic Preconditioning
- Beta-blockers
- Statins
- Alpha-2-agonists (good in ppl who cant take B.Blockers)
- Calcium channel blockers
Is isoflurane an appropriate anesthetic agent to use during cardiac surgery? Why or why not?
Isoflurane has been associated with Coronary Steal (shunting blood from poorly perfused areas to better perfused) causing worsening ischemia.
In reality, coronary steal is not that big a deal - don’t use Iso if pt has severe hypotension.
What are collateral blood vessels in the heart? How are they formed?
- develop between branches of occluded and non-occluded arteries and can contribute a significant amount of blood flow
- They originate from pre-existing arterioles that undergo proliferative changes of the endothelium and smooth muscle
What is ischemic preconditioning in the heart?
single or multiple brief periods of ischemia can be protective against a subsequent prolonged ischemic insult. The brief periods of ischemia appear to “precondition” myocardium against reversible or irreversible tissue injury, including stunning, infarction, and the development of malignant ventricular arrhythmias
What is anesthetic preconditioning in the heart?
effects that mimic IPC
K+ATP channels play an important role
which part of heart supplies diagonal branches?
LAD
which part of heart supplies obtuse marginals?
Left Circumflex
What controls coronary blood flow?
Vascular resistance
What controls vascular resistance?
Neural control Metabolic control Endothelial control Autoregulation Extravascular compressive forces
Blood flow through thecoronarysystem is regulated mostly by __________ ?
local arteriolar vasodilation
What 2 things help create collateral blood flow?
Monocyte chemoattractant protein-1 (MCP-1)
Vascular endothelial growth factor (VEGF)
normal coronary blood flow?
- 70 ml/min/100 g of heart weight,
- 225 ml/min
- 4 to 5 percent of the total cardiac output
What of the heart is the most important physiological mechanism regulating coronary vascular resistance
Metabolic activity
what mechanisms are responsible for metabolic control?
Nitric oxide
Adenosine
Prostaglandins
K+ATP channels
(causes increased blood flow and vasodilation)
