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What is the most common cause of death in the US?
Ischemic Heart Disease (IHD) - 35%
What percentage of patients undergoing surgery in the US have IHD?
List non-modifiable risk factors for IHD
- 1) Increasing age
- 2) Male gender
- 3) Genetic predisposition/family history
List modifiable risk factors for IHD
- 1) Cigarette smoking
- 2) Hypertension
- 3) Obesity
- 4) Sedentary lifestyle
How does hypertension increase the risk of coronary events?
- 1) Direct vascular injury
- 2) LV hypertrophy
- 3) Increased myocardial oxygen demand (MvO2)
What are questions to consider during preoperative assessment of a patient with hypertension?
- 1) Is it well-controlled?
- 2) Is the pt compliant with treatment?
- 3) What is the procedure?
- a. Colonoscopy vs craniotomy
- 4) What medications are being used?
- 5) What meds has the pt received before surgery?
List partially modifiable risk factors for IHD
- 1) Elevated cholesterol/triglycerides
- 2) Hyperglycemia/diabetes
- 3) Low HDL levels
List other considerations for IHD
- 1) Personality type
- a. Type-A are difficult to deal with
- 2) C-reactive protein: active vs bystander?
- a. Is elevated C-reactive protein causing the problem?
- b. Is the problem causing elevated C-reactive protein?
What 2 vessels supply the entirety of myocardial blood?
- 1) Left main coronary
- 2) Right coronary
What structures does the RCA supply?
- 1) RA
- 2) Most of the RV
- 3) LV inferior wall (varies)
What portion of the population has right-dominant circulation?
70-80% of people
What does the RCA supply in right-dominant circulation?
- 1) PDA
- 2) Posterior LV
- 3) Superior-posterior intraventricular (IV) septum
- 4) Inferior wall
What portion of the population has left-dominant circulation?
10-15% of people
What is unique about left-dominant circulation?
- 1) Circumflex artery supplies the PDA
- 2) Cx wraps around the AV groove
- a. Continues down as the PDA also supplies most of the posterior septum and inferior wall
What portion of the population has co-dominant circulation?
15-20% of people
What is unique about co-dominant circulation?
Both Cx and RCA supply PDA
What structures does the left coronary artery (LCA) supply?
- 1) LA
- 2) Most of
- a. IV septum
- i. Bundle branches here
- b. LV
- i. Septum
- ii. Anterior wall
- iii. lateral wall
What does the left main artery bifurcate into?
What structures does the LAD supply?
- 1) Septum
- 2) Anterior wall
- What structure does the Cx supply?
- Lateral wall
What vessels supply the SA node?
- 1) RCA in 60% of people
- 2) LAD in 40% of people
What vessels supply the AV node?
- 1) RCA in 85-90% of people
- 2) Cx in 15-20% of people
What vessels supply the Bundle of His?
- Dual blood supply
- 1) LAD
- 2) PDA
What vessels supply the anterior papillary muscles of the MV?
- 1) Diagonal branches of LAD
- 2) Marginal branches of Cx
What vessel supplies the posterior papillary muscles of the MV?
PDA alone supplies these muscles
What papillary muscles are more vulnerable to ischemic dysfunction?
Posterior papillary muscles - singular blood supply
What is significant in knowing which vessels supply papillary muscles?
Anticipated papillary muscle dysfunction with vessel occlusion and subsequent MV incompetence
What is normal coronary blood flow?
What portion of the myocardium is supplied directly by blood within chambers of the heart?
- The inner 0.1mm endocardial surface
- This is an insignificant amount of perfusion
- Almost no perfusion by this method during systole
What vessels supply most of the myocardium?
Epicardial vessels - outer surface vessels
What vessels penetrate the myocardium?
Describe subendocardial arteries.
- A plexus of vessels located immediately beneath the endocardium
- What is unique regarding coronary blood flow during the cardiac cycle?
- Intermittent flow.
- During contraction, intramyocardial pressures in the LV approach systemic arterial pressure
- Force of LV contraction totally occludes intramyocardial part of coronary arteries
- Even during the late part of diastole, LV pressure exceeds RA pressure
When is the LV most susceptible to ischemia? (test question)
How does elevated end diastolic pressure (LVEDP) due to fluid overload affect CPP?
How is CPP determined?
ADP-LVEDP = CPP
How is the RV perfused during both systole and diastole whereas the LV is only perfused during diastole?
RV has less force of contraction during systole and does not totally occlude intramyocardial vessels
What portion of CO makes up coronary blood flow?
What are the 4 determinants of coronary blood flow?
- 1) HR
- 2) CPP
- 3) Arterial oxygen content (CaO2)
- 4) Coronary vessel diameter
How does HR affect coronary blood flow?
- Determines diastolic time
- Increased HR results in decrease in coronary perfusion due to disproportionate reduction in diastolic time (% of cardiac cycle)
What are the determinants of CPP?
- 1) Aortic pressure - supply side of CPP (preload)
- 2) LVEDP - resistance side of CPP (afterload)
What measure is more important for determining CPP? MAP or ADP?
What variables can REDUCE CPP?
- 1) Decreased ADP
- 2) Increased LVEDP
What are determining factors of CaO2?
- 1) Arterial oxygen tension
- 2) Hgb concentration
- CaO2 = (SaO2 * Hgb * 139) + (0.0031 * PaO2)
- This formula demonstrates that oxygen saturation and hemoglobin level have a greater influence on arterial oxygen content than does partial pressure of oxygen
How is oxygen delivery calculated?
DO2 = CaO2 * CO
Why is it significant that hemoglobin has a greater affect on oxygen delivery than PaO2?
During single-lung ventilation, knowing the patient's hemoglobin level is adequate (>10) allows the patient to tolerate abnormally low PaO2 levels
What are the 4 determinants of coronary demand?
- 1) Basal requirements
- 2) HR
- 3) Wall tension
- 4) Contractility
What is the most important determinant of myocardial blood flow?
Myocardial oxygen demand
What contributes to myocardial oxygen requirements?
- 1) Basal requirements
- 2) Electrical activity
- 3) Volume work
- 4) Pressure work
What percentage of oxygen is extracted by the myocardium?
What is normal coronary sinus oxygen saturation?
How does myocardium compensate for increased metabolic demand?
- Increased coronary blood flow
- Myocardium cannot extract more oxygen from hemoglobin like other tissues
What components of wall tension affect myocardial oxygen demand?
- 1) Preload (ventricular radius)
- 2) Afterload
What is the primary substance considered regarding the body's natural ability to increase blood flow?
List vasodilator substances that promote coronary blood flow
- 1) Adenosine
- 2) K+ ions
- 3) H+ ions
- 4) CO2
- 5) Bradykinin
- 6) Prostaglandins
- 7) Nitric oxide
Why are NSAIDS contraindicated in patients with IHD or CKD?
They inhibit prostaglandin synthesis and thereby decrease ability of coronary and renal artery vasodilation to a degree
Describe the direct effects of the peripheral nervous system on coronary blood flow
- ACh released from vagus nerve stimulation
- PNS distribution is not extensive to coronary arteries, but ACh release will cause
- 1) Vasodilation
- 2) Slowed HR
What substances are responsible for direct SNS contributions to coronary blood flow?
- 1) Epinepherine
- 2) Norepinepherine
Describe SNS innervation of the heart and coronaries
Describe the location and effect of direct SNS stimulation on a1 receptors. (with regards to coronary flow)
- Located predominantly in epicardial vessels
- Excess stimulation can cause vasospastic myocardial ischemia and angina
Describe the effect of direct SNS stimulation on 1 receptors. (with regards to coronary flow)
- 1) Cardioacceleration (increased HR)
- 2) Positive inotropy (increased contractility)
Describe the location and effect of direct SNS stimulation on 2 receptors. (with regards to coronary flow)
- 1) Located mainly in
- a. Smaller intramuscular vessels
- b. Subendocardial vessels
Describe how indirect effects of SNS or PNS stimulation is more important than the direct effects.
Increased metabolic requirements caused by epi/NE offset by local blood flow regulatory mechanisms that dilate the coronary arteries.
What processes supply the heart's energy?
- 1) Fat metabolism - 70%
- a. Preferential breakdown of fatty acids
- 2) Glycolysis
- a. Does not fully meet energy needs
What are the 3 primary sources of venous return for the heart muscle?
- 1) Coronary sinus
- 2) Anterior cardiac veins
- 3) Thebsian veins
What is the flow of coronary sinus drainage?
LV to RA
What vessel drains the RV to the RA?
Anterior cardiac veins
What is the role of thebsian veins in venous return?
- Account for small portion of coronary venous return
- Empty into all chambers of the heart, technically causing a right to left shunt but insignificant
How is the myocardium perfused in the presence of coronary blockage during CPB?
- Retrograde flow through coronary veins
- Veins lack valves which allows backward flow
List the 4 causes of an MI due to IHD
- 1) Atherosclerosis
- 2) Coronary thrombus
- 3) Coronary embolus
- 4) Coronary artery spasm
How is Poiuselle's law related to atherosclerosis?
Because radius is raised to the 4th power in determining flow, reducing the artery's radius by 50% results in a 16-fold reduction in flow (flow becomes 1/16 of normal)
Describe the process of atherosclerotic occlusion of coronary arteries.
- 1) Cholesterol becomes deposited beneath endothelium of the coronary artery
- 2) Gradually these areas are invaded by fibrous tissue and frequently become calcified, becoming atherosclerotic plaques
- 3) These plaques can extend into the lumen of coronary arteries to partially or totally occlude flow
Describe the process of occlusion due to coronary thrombosis.
- If an atherosclerotic plaque breaks through the intima of a coronary artery and comes into contact with blood:
- 1) Platelets adhere to its unsmooth surface
- 2) Fibrin will be deposited
- 3) RBCs become entrapped
- 4) Resulting blood clot can expand to totally occlude the vessel
Describe the process of occlusion due to coronary embolus
A thrombus breaks loose from its atherosclerotic plaque and occludes a more distal segment of a coronary artery
Describe the process of occlusion due to coronary artery spasm
- Thrombus formed as the result of blood stasis from vasospasm
- Thought to be a potential source for the development of a secondary thrombus
What are the 4 results of IHD?
- 1) Partial coronary obstruction
- 2) Loss of autoregulation
- 3) Angina pectoris
- a. Probably due to glycolysis and lactic acid production
- 4) Mortality
- a. Highest with left main involvement
- b. Second highest with LAD involvement
What diagnostic tools are used for diagnosis of IHD?
- 1) Stress EKG
- 2) Noninvasive imaging
- 3) Cardiac catheterization
What is a stress EKG useful for detecting?
- 1) Signs of ischemia and their relationship to chest pain
- 2) Appearance of a new murmur of MR
- 3) Decrease in BP during exercise
What area of tissue is damaged in a non-transmural MI (NSTEMI)?
What is unique about EKG changes of a NSTEMI?
- Baseline voltage prior to QRS is ELEVATED
- ST-segment appears DEPRESSED relative to baseline
What area of tissue is damaged in a transmural MI (STEMI)?
Full-depth tissue damage
What is unique about EKG changes of a STEMI?
- Baseline voltage prior to QRS is DEPRESSED
- ST-segment appears ELEVATED relative to baseline
- Q-wave seen because electricity viewed is moving in opposite direction (toward other side of heart)
What are the 2 types of noninvasive imaging?
- 1) Echocardiography
- 2) Nuclear stress imaging
- a. Pharmacologically induced stress (dobutamine, adenosine, dypyridamole)
- b. Imaging to assess wall motion and/or tracer uptake to assess perfusion (thallium, technetium)
What is the gold standard for determining condition of coronary arteries?
What noninvasive test can now be performed to identify the presence of atherosclerotic plaques in coronary arteries?
What are the indications for cardiac catheterization?
- 1) Angina pectoris refractory to maximal medical therapy
- 2) Patients being considered for emergency revascularization
What are the 3 main treatment categories for ischemic coronary disease?
- 1) Behavior modifications
- 2) Medical management
- 3) Medical/surgical intervention
What behavioral modifications are expected in treating ischemic coronary disease?
- 1) Stop smoking
- 2) Reform diet - lose weight
- 3) Exercise
- These 3 things alone may lower BP and improve life expectancy
- 4) Chill out
What 5 classes of medications are used in medical management of ischemic coronary disease?
- 1) Beta blockers
- 2) Calcium-channel blockers
- 3) ACE inhibitors
- 4) Antiplatelet drugs
- 5) Nitrates
Describe the sequence of events by which beta blockers reduce myocardial oxygen requirement.
- 1) Block sympathetic beta-adrenergic receptors
- 2) Decreased sympathetic activity
- 3) Decreased HR
- 4) Decreased cardiac metabolism during stress
- 5) Decreased MvO2
What do calcium channel blockers do in the treatment of ischemic coronary disease?
- 1) Decrease HR and SVR during exercise
- 2) Dilate coronary arteries and relieve spasms
- 3) Can decrease contractility and INCREASE the rate of reinfarction
What are ACE inhibitors being replaced by?
Digitalis - cardiac glycocide therapy
What antiplatelet drugs are used in treatment of ischemic coronary disease?
- 1) Low dose ASA
- 2) Plavix
- 3) Ticlid
What can be accomplished through invasive cardiology in treating ischemic coronary disease?
- 1) Angioplasty
- 2) Stents
- 3) DCA
- 4) Lasers
- 5) And more
What is a special consideration regarding a patient with drug-eluding stent placement?
Patients with these stents require much longer antiplatelet therapy before they can safely discontinue medication prior to surgery.
What is appealing about receiving CABG today for patients?
- 1) Low mortality rate
- 2) High percentage of graft patency out to 10 years
- a. More with lifestyle modifications
- 3) Relieves angina in 85% of patients
What are the 4 causes of death after MI?
- 1) Pump failure
- 2) Pulmonary edema
- 3) Ventricular fibrillation
- 4) Ventricular rupture
What type of pump failure involves a dysfunction of ventricular ejection?
What type of pump failure involves a dysfunction of ventricular filling?
What is the cause of decreased cardiac output in pump failure?
- Ventricular stretch/cardiogenic shock, dyskinesis
- Volume of stretched bulge is immediately removed from net SV and therefore CO
Damming of blood in the pulmonary blood vessels can lead to death from what?
What is unique to the timing of death from pulmonary edema?
Often a delayed symptom (several days) as the result of diminished renal perfusion over days. This leads to decreased urinary excretion and subsequent increased TBV in a compromised pump.
What are the 4 primary causes of ventricular fibrillation causing death after an MI?
- 1) Rapid depletion of K+ ions from ischemic musculature;
- a. increased extracellular K+ causes cardiac irritability
- 2) Injury current
- a. Ischemic muscle unable to completely repolarize membranes after each heartbeat
- 3) Increased sympathetic responses from MI cause muscle irritability
- 4) LV dilation causes increased conduction pathway and abnormal pathways
Describe the process of ventricular rupture.
Days after an MI, dead muscle fibers begin to degenerate and the heart wall becomes stretched very thin. Dead muscle bulges outward severely with each contraction and this systolic stretch can ultimately rupture.
What are the major treatments of MI?
- 1) MONA
- 2) Thrombolytics if within window of opportunity
- 3) Anticoagulation
- 4) Beta blockers
- 5) Arrhythmia management
- 6) Rest
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