EKG Basics Part 3 Flashcards
Define angina, ACS, unstable angina, and MI.
- Angina = classic symptom of cardiac ischemia, typically described as diffuse chest pain or pressure that radiates.
- ACS = acute coronary syndrome, which is an urgent situation characterized by a compromised coronary blood supply. Results in either unstable angina or MI.
- Unstable angina = same as angina, but has a variable pattern and is typically more severe.
- MI = myocardial infarction, the classic heart attack that comes in two primary etiologies.
Why do ST segments not always elevate in NSTEMIs?
- NSTEMIs are characterized by reduced blood flow, rather than blocked blood flow.
- Usually presents with depressed ST segments.
Why do ST segments change in MIs?
- Normal myocardium vs ischemic myocardium creates a voltage gradient.
- This voltage gradient shifts injury currents, and therefore ST segments.
What characteristics make a plaque most likely to rupture?
- High inflammatory cell count.
- Thin fibrous cap
- Large pool of lipids
- Small size = more unstable (not a good predictor)
Describe an etiology that can result in myocardial infarction without obstruction of a coronary artery.
- Extreme tachycardias
- Severe hypotension due to blood loss (hemorrhagic shock)
Both result in hypoperfusion of the myocardium.
What 3 demographics tend to present with atypical chest pain?
- Diabetics
- Women
- Elderly
Which of these are poor predictors of the severity of an MI?
- Angina severity
- Response to SL NTG
- Elevated troponin
- EKG changes
- Angina severity
- Response to SL NTG
The best indicator is an EKG.
Troponins can technically be elevated in other conditions.
Why are troponin levels preferred over CK-MB enzyme tests for diagnosing an MI?
- Troponin elevates within 2-3 hours and stays elevated for days.
- CK-MB takes up to 6 hrs to elevate and goes to normal within 48 hrs.
What are the 3 stages of a typical acute STEMI?
- T-wave peaking followed by T-wave inversion. (A/B)
- ST-segment elevation (C)
- Appearance of new Q waves. (D)
A STEMI doesn’t have to go through all 3 stages everytime. It can skip stages.
What specific characteristic would make a T wave inversion more likely to be MI instead of VH or a BBB?
Symmetrical inversion
Image B shows a much faster downslope.
What is pseudonormalization of T waves?
- In a patient with T wave inversion at baseline, ischemia can revert it to normal.
- Requires a previous EKG for comparison.
In what leads are T-wave inversions normal?
In young people, children:
- V1
- V2
- V3
aVR is also always supposed to be inverted T wave.
In black athletes, it can persist and turn into persistent juvenile T-wave pattern.
What is the most diagnostic of the 3 stages of an acute STEMI?
ST elevation, aka what it is named for.
It also is a strong sign that the MI will worsen unless we intervene.
How is a ST-segment determined to be elevated from baseline?
Comparison to TP and PR segments. (preferably TP)
PR can be depressed in pericarditis.
If ST-segment elevation persists, what is most likely going to occur secondarily?
Ventricular aneurysm
Normally, they return to normal within a few hours.
What is J point elevation?
- Junction point elevation, where the ST segment takes off from the QRS.
- It suggests an early repolarization.
Normal finding!
How do you differentiate between J point elevation and ST elevation?
- ST elevation shows a configuration in which it is bowed upwards and joins the T wave seamlessly.
- J point elevation shows an independent T waveform.
What is the suggested diagnostic criteria guidelines for confirming ST elevation?
- Leads V2 or V3 must demonstrate at least 2.5mm STE (less over 40 or woman)
- Other leads must show at least 1mm STE (same for all)
- ST elevation must be present in at least 2 contiguous leads.
Appearance of what kind of waveform is diagnostic for myocardial infarction?
New Q waves.
Implies irreverisble myocardial cell death has occurred.
Any electrode placed over the area that had an infarct will become negative since electricity doesn’t flow through that area anymore.
What is a reciprocal change?
- Leads that are generally opposite of the leads closest to an infarct will have increased electricity towards them.
- ST depression may occur away from areas showing STE.
What is pathologic Q wave criteria?
- Q wave longer than 0.04s in duration
- Q wave at least 25% of height of the R wave in the same QRS complex.
pathologic Q waves should be present in contiguous leads.
DO NOT USE aVR for Q wave pathology criteria, since it normally has a deep Q wave.
Which of these leads meet Q wave pathology criteria?
- Lead I: significant
- Lead aVR: not significant since it is aVR and expected.
- Lead V2: too shallow and narrow.
- Lead aVF: significant
Where does an inferior infarction occur? Occlusion of what coronary artery is the cause? What leads should be most affected?
- Occurs on the diaphragmatic surface of the heart.
- Occlusion of RCA (right coronary) or its descending branches.
- Changes in II, III and aVF (all 3 point downwards)
Where does a lateral infarction occur? Occlusion of what coronary artery is the cause? What leads should be most affected?
- Occurs on the left lateral wall of the heart.
- Occlusion of the LCx artery. (left circumflex)
- Changes in I, aVL, V5, and V6 (Left lateral leads)
