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Reasons to stop a stress test.
- Severe angina
- Hypotension
- Marked arrythmia
- Severe fatigue, leg pain, or breathlessness
- ST depression or elevation
- AV bundle branch block.
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Excercise stress test contradictions
- Unstable Angina
- Arrythmias
- Acute illness
- Critical Aortic Stenosis
- Advanced AV block
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Radiopharmaceuticals that can be used for a First Pass Cardiac Study
Tc-99m DTPA
or
Any non particulate radiopharmaceuticals
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Reasons for performing a First Pass Study
Determine Ejection Fraction
Evaluate and detect intra cardiac shunts.
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Views used in First Pass Study to determing right EF and left EF.
Right EF = RAO
Left EF = LAO
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What is a MUGA study used to determine?
Left ventricle EF and Wall motion
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What are the techniques for labeling RBC's? also the pros and cons of each ?
- Invivo-
- problem--not all pertechnetate tagged to RBC, so accumulates in salvary glads, gastric mucosa and thyroid,
- Invitro- blood sample collected
- highest labeling efficiency
- modified invivo- less blood handeling, better efficiency than invivo.
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Hypokinesis
Low wall motion
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Dyskinesis
outward motion during Systole
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Stroke volume
The blood ejected by ether ventricle during ventricular systole
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Cardiac output
volume of blood heart pumps per minute
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End Disastolic volume
Capacity of ventricle after it is completely filled with blood. THe largest volume reached by ventricle during the cardiac cycle.
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End Systolic Volume
The residula capacity of the ventricle at the end of contraction. THe smallest volume reached during the cardiac cycle.
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Ejection Fraction
Percent of blood ejected from venticle during each contraction.
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LAD supplies
- The Left Anterior Desending supplies
- the anterior wall,
- most of the Septum
- the distal portin of the Apex
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The Left Circumflex supplies
posterior and lateral walls of the left ventricle.
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The RCA supplies
The Right Coronary Artery supplies the inferior wall of the left ventricle and the right side of the heart
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Formula to calculate ejection fraction
Diastole-systole / diastole * 100%
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Drugs that should be discontinued prior to stress
- caffine
- beta blockers
- viagra
- calcium channel blockers
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Patient Prep for Stress test
- NPO 4-12hrs
- No caffine, dairy or sugar
- PAtient should be advised of excersise in advance
- prepare 10- lead ECG
- start iv
- Obtain baseline BP
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Target Heart Rate =
.85 * (220-age) = target heart rate
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Risk Factors for CAD
- high BP
- high cholestorol
- smoking
- obesity
- diabetes
- sedentary life style
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Perfusion imaging drug that cand determine viability, and has ability to redistribute
thallum is the only one with the ability to redistribute.
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What is Atherosclerosis?
When fatty substances, like triglycerides, and cholestorol are deposisted in the walls of medium and large diameter arteries.
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which ECG wave triggers the camera to aquire counts.
R wave.
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Define stunned myocardium:
- Abnormal contraction but
- normal coronary blood flow.
May persist for days/weeks following angioplasty or thrombolytic therapy, making it difficult to assess the therapy.
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Define hybernating myocardium:
Reduced perfusion and contraction resulting in chronic LV dysfunction.
in this situation identify viable myocardium to select for revascularization.
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"Pacemaker of the heart"
SA node
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Initates contraction
SA node
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generates impulses of 60-100bpm
SA node
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"gate keeper of ventricles"
allows 40-60bpm
AV node
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Slows impulse transmission
AV node
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carry impulses to tips of both ventricles
AV bundles
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Terminal branch for two bundle branches
Purkinhe Fibers
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____carry impules to individual myocardial cells resulting in_______
Purkinje fibers carry impulses to individual myocardial cells resulting in simultaneous contractions of both ventricles.
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P wave
Initated by SA node
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P-R interval
Time from beginning of atrial contraction to beginning of ventricular contraction.
impulse from AV node to purkinje fibers.
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QRS complex
Depolarization of both ventricles immediately precedes their contraction
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ST segment
Represents early repolariztion (recovery) of ventricles.
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T Wave
Ventricular repolariztion
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Repolarization of Atria
Not seen on ECG!! because it is obsured by QRS complex
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Wave that is present in hypokalemia?
U WAVE!
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Normal P-R interval
.12-.20 sec (3-5 small squares)
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normal duration of QT interval
.36-.44
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Sinus arrythmia
all is normal except R-R intervals
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Sinus Bradycardia
everything normal except slowed rate, less than 60bpm
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Premature Atrial contractions
- P waves early, may look smaller, or peaked,
- P-R interval usually shorter.
- R-R varied
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No P-wave before, unusally tall and wide QRS, T-wave may be below baseline.
Premature Ventricular Contractions.
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Fast constant firing of ectopic focus, F-waves instead of P-waves.
Atrial Flutter
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Irregular R-R interval, and F waves instead P-waves
Atrial Fibrillation
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supraventricular tachycardia
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P-R interval greater than .20 sec
Heart block
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Some P-waves not followed by QRS or T-wave because
impulse was blocked.
P-R interval become longer and longer until no QRS. than will be normal.
second degree heart block
- (wenckebach) MOBITZ type 1
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everything normal except some P-waves are not followed by QRS or T-wave?
- Second Degree Heart Block
- (MOBITZ TYPE2)
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AV node is completly blocked, so no relationship between P wave and QRS complex/ t-wave.
3rd Degree AV Heart BLock
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2nd degree heart block
Morbitz type 1
WENCKEBACH
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2nd degree heart block
MOBITZ TYPE2
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3rd Degree Heart Block
complete heart block
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define ischemia
A deficency of blood resulting from ablockage or constriction of a blood vessel
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4 characteristic of ideal myocardial perfusion agent
- 1. High first pass extraction proportional to blood flow
- 2. High target to non target ratio
- 3. Must remain in myocardium long enough to image.
- 4. able to complete stress and rest on same day.
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Tl-201 mech of action
High extraction efficency by myocardial cells. by active transport Na-K pump
slower clearance from under perfused areas.
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Tc-99m mibi
high liver uptake, clears from hepatobiliary system faster than myocardium.
passive diffusion into mitochondrial membranes.
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Adenosine;
-mech of action
-plasma half life
Activates adenosine receptors on cell membranes of endothelium and smooth muscle of coronary arteries.
mediator of vasodiator action
half life <10sec
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Dipyridamole:
mech of action
half life
counter
Inhibits clearnce pathway of adenosine into cells. Extracellular adenosine taken up by receptors on cell membrane of endothelium and smooth muscle of coronary arteries.
coronary arteries dilate and blood flow increases to normal arteries.
half life 15-30 min.
counter: IV aminophylline, blocks adenosine receptors.
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Lexiscan:
mech of action
half life
Produces coronary vasodilation and increases coronary blood flow by activating the A2 adenosine receptors.
Half life: 2hrs
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Dobutamine:
mech of action
half life
counter
Increases force of mycardial contraction and oxygen demand by stimulating beta receptors in the heart.
half life: 2 min
counter: Beta blockers.
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