Lecture 10: Ischemic Heart Disease Part 2 Flashcards
What is always the initial test for anyone presenting with chest pain?
EKG
How fast should an EKG be done if someone presents with ACS symptoms to the ER?
10 minutes!
if the initial EKG is not diagnostic but the patient remains symptomatic and there is high clinical suspicion for ACS, what should be done?
serial EKGs (15-30 min intervals in the first 1-2 hours) should be performed to detect ischemic changes
what is the earliest presentation of ACS that can be seen on EKGs
Hyperacute T waves
Only exists 20-30 minutes after MI so rarely seen in clinical practice
what do hyperacute T waves have to be distinguished from
peaked T - waves assocaited with hyperkalemia
what are the findings indicating suspicion for NSTEMI and STEMI
i think its not a bad idea to know this chart
this chart would not be bad to memorize either
chart defining evolution of STEMI in EKG
after ordering an EKG, what is step two in evaluating a pt with s/s of ACS
order cardiac biomarkers!
aka cardiac enzymes
What are the 3 types of cardiac enzymes we can order?
- Myoglobin
- CK-MB
- Troponin I, T (the best)
This comes AFTER EKG.
what is troponin
a contractile protein that is NOT normally found in the serum
only relesed when myocardial infarction occurs!!
Why are troponins the preferred marker for myocardial study?
- highly sensitive AND specific for even small amounts of cardiac damage
- ONLY RELEASED when myocardial necrosis occurs.
when do troponin serum levels increase, peak and return to baseline?
- Increases within 3-6 hours
- Peaks within 24-48 hrs
- Takes 5-14 days to recover.
How often should we repeat troponin?
- Initial presentation
- 90 Minutes
- 6-8 hrs after x3 or unil trending down.
What are we specifically looking for in serial troponin readings?
A trend, trends have more weight than a single reading!
what are other potential causes of elevated troponin?
How long does it take serum CK-MB levels to increase, peak and return to baseline
Increase 4-8 hrs after injury
Peak around 24 hrs
Return to normal by 48-72 hrs
What is considered a positive CK-MB?
if CK-MB > 5% of total CK
Not preferred test (less sensitive and specific than troponin)
What might cause a false positive of CK-MB?
- Exercise
- Trauma
- Muscle disease
- DM
- PE
What cardiac biomarker is the earliest marker for MI?
Myoglobin
Highly sensitive, but poor specificity.
Could appear within 2 hrs.
what is myoglobin
found in cardiac and skeletal muscle
most sensitive early marker for myocardial infarction
what is lactate dehydrogenase (LDH)
found in many tissues (kidneys, skeletal muscles, brain, blood cells, lungs, liver) so it is very non-specific!
How long does it take LDH to increase, peak and return to baseline
Rises within 24 - 72 hrs after MI
Peaks in 3 - 4 days
Returns to normal in ~14 days
What is the order of enzyme elevation in ACS?
- Myoglobin
- CK-MB
- Troponin
- LDH
Trop takes longer to elevate.
What 3 lab levels may elevate as a result of ACS? how long do these take to rise/fall?
- Leukocytosis (within several hours, peaks at 2-4 days, falls within a week)
- ESR (rises within 3 days, may be elevated for weeks)
- CRP ( no timeline specified)
patients w/o biochemical evidence of myocardial necrosis but with elevated _____(what lab)_____ are at risk of subsequent ischemic events
Elevated CRP
what are stress tests used to evaluate?
inducible ischemia in patients with angina
what are the 2 ways stress tests can be done
- via exercise (PREFERRED)
- via pharmacologic measures
What is the general minimum for doing an exercise stress test?
- Walk 5 minutes on flat ground
- 1-2 flights without stopping
What are the indications for a stress test?
- Confirm angina
- Determine severity of limitation due to angina
- Assess prognosis of known CAD and MI recovery
- Evaluate response to therapy
Who is an exercise stress test most useful for?
- Low pretest likelihood and normal baseline EKGs
- Best in young, females with atypical symptoms.
what are limitations to exercise (only) stress testing
- More false-positives than true-positives
- Not a screening tool in asymptomatic patients
What is the max HR for a stress test and the finding that makes it positive?
- 85% of max HR (220-age)
- ST depression of 1mm = positive
what is the MC protocol used in exercise stress testing
Bruce treadmill protocol
The intensity of exercise is periodically increased, continuing until what occurs
- The patient reaches maximum HR
- Changes in heart function are detected on the EKG
- Patient is symptomatic
what is the equation for HR max
220 - age
When do you absolutely need to terminate a stress test?
- SBP drop of 10mm Hg from baseline BP despite increasing workload, when accompanied by other evidence of ischemia or hypoperfusion
- Mod-severe angina
- Nervous system symptoms (ataxia, dizziness, enar-syncope)
- Poor perfusion (cyanosis, pallor)
- Subject wants to stop
- Sustained Vtach
- ST elevation >1mm without Q-waves
What are the absolute contraindications to TMSTs? (treadmill stress tests)
- Acute MI within 2d
- High-risk, unstable angina
- Uncontrolled arrhythmias resulting in hemodynamic instability
- Severe, symptomatic AS
- Uncontrolled symptomatic HF
- Acute PE
- Acute myocarditis or pericarditis
- Acute aortic dissection
- preexcitation syndrome (WPW syndrome)
- electronically paced ventricular rhythm
- greater than 1mm of resting ST depression
- complete LBBB
When do we add imaging to an exercise stress test?
- Resting EKG is difficult to interpret (LBBB, baseline changes, low voltage)
- confirm a positive test in a asymptomatic pt
- localize the region of ischemia
- distinguish ischemic from infarcted myocardium
- assess completeness of revascularization following bypass surgery or coronary angioplasty
- as a prognostic ingicator in patients with known coronary disease
What scan is associated with a nuclear stress test?
SPECT (single photon emission CT)
this provides perfusion data following injection of a radioactive material prior to stress test and then compared after stress test.
when would you add a stress Echo to an exercise stress test
- in attempt to increase specificity and sensitivity of test
- determine extent of myocardium at risk for ischemia
- looking for regional wall motion abnormalities or LV dilation in response to exercise
when is a pharmacologic stress test used
Used when a patient is unable to exercise to a sufficient cardiac workload or has a contraindication to or a clinical reason not to perform an exercise stress test
Ex. LBBB, V paced rhythm, beta blocker or CCB therapy, large AAA
Why does a pharmacological stress test require imaging?
Sensitivity of a pharmacologic stress EKG is very low, so these tests are always combined with an imaging modality
what are the preferred pharmacologic stress agents
vasodilators
What are the 3 vasodilators used for pharmacological stress tests? what do these do?
- Adenosine
- Dipyridamole
- Regadenoson
cause direct CORONARY ARTERY VASODILATION
Preferred agents.