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.
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)
Where does an anterior infarction occur? Occlusion of what coronary artery is the cause? What leads should be most affected?
- Occurs on the anterior surface of the left ventricle.
- Occlusion of the LAD (left anterior descending)
- Changes in V1-V4.
adding V5 and V6 would make it anterolateral.
Where does a posterior infarction occur? Occlusion of what coronary artery is the cause? What leads should be most affected?
- Occurs on the posterior surface of the heart.
- Occlusion of the RCA (Right coronary)
- Reciprocal changes in anterior leads are more expected. (EX: tall R waves in leads V1, V2, V3)
Isolated posterior infarcts are rare, and usually accompany inferior or lateral infarcts.
What is the quick way to diagnose poor R-wave progression, and what might it signify?
- If the R wave of V3 is < 3 mV, poor progression.
- Poor R-wave progression can suggest anterior MI.
Poor R-wave progression can also be seen in RVH, chronic lung diease, obesity, and poor electrode placement.
What are deWinter’s T waves?
Peaked, symmetrical T waves that originate from upsloping ST depression.
2% of all acute LAD occlusions present with this instead of STE.
What are Wellens’ waves?
- Deeply inverted or biphasic T waves in V2, V3, or V4.
- In biphasic, the upright portion tends to occur first for wellens’.
Predicts proximal occlusion of LAD.
For a posterior infarction, what leads do we look at and what should we expect?
- Reciprocal changes in V1 are the most common, but look at anterior leads in general.
- Tall R wave with ST depression is suggestive of posterior MI. (esp. if R wave > S wave in same lead)
Typically will present with inferior STE and anterior ST depression.
No conventional leads overlie the posterior wall.
Do not get confused with RVH, which requires right axis deviation also.
