ECG - MI and ischaemia Flashcards
Where is ischaemia confined to in partial arterial occlusion?
Subendocardial tissue
Where is ischaemia confined to in complete occlusion of a cornary artery?
Full thickness of myocardium
Which way does necrosis occur in MI?
From subendocardial tissue outwards
What happens to T waves in the first few minutes of MI?
T-waves become taller in hyperacute setting
What is the ST segment?
Distance between S wave/end of QRS complex and beginning of T-wave
What happens to the ST segment during the hyperacute phases of STEMI?
Rises - thought to be due to injury current in direction of ECG leads
What follows hyperacture changes (ST elevation and increased T wave amplitude) in terms of ECG changes?
R waves can increase, and S waves can disappear - progressive ischaemia and destruction of purkinje fibers
What ECG changes occur if STEMI results in full thicnkess necrosis?
Q-waves - ECG leads looking directly at infarcted area
Why do q-waves occur in full thickness MI?
Due to infarcted tissue (with no electrical activity) acting as a window to the live muscle in other areas of the heart. Normally the infarcted area can drown out depolarisation vectors in other areas of the heart. When this dies, other vectors become more prominent on ECG
Why does T-wave inversion occur in MI?
Variable timing - may reflect reperfusion of area either due to intervention or dynamic changes in clot formation. May persist following MI or may resolve
What can early Q-waves in MI indicate?
Electrically stunnned myocardium - still potentially salvagable with intervention
How soon after onset would you see ST elevation in an MI?
<20 minutes
What does the right coronary artery supply?
- RV - through marginal branch
- Inferior surface of ventricles - posterior descending artery
- Inferior third of IV septum - posterior descending artery
Where does ischaemia occur with blockage of the RCA distal to the marginal artery?
Inferior walls of the ventricles
If someone had completely occluded their RCA distal to the marginal artery, where would you expect to see ECG changes?
- Inferior leads (II, III and aVF) - will see injury current (ST elevation) in these leads
- Lateral leads (I and aVL) - Reciprocal ST depression
What areas will blockage of the RCA proximal to the marginal artery affect?
Inferior walls of ventricles and anterior wall of RV
What does the left coronary artery divide into?
Left anterior descending artery and left circumflex artery
What does the LAD supply?
Anterior wall of LV and anterior 2/3rds of IV septum
What leads look at the IV septum?
V1 and V2
What leads look at the anterior surface of the LV?
Leads V3 and V4
What will proximal occlusion of the LAD result in in terms of ECG changes in a stemi?
- ST elevation in leads V1-V4 - anterior MI
- May show Reciprocal ST depression in inferior leads
What does the left circumflex artery supply?
Posterior and high lateral wall of the LV
Where are ECG changes most prominent in complete occlusion of left circumflex artery?
Lateral leads - aVL, I, V5-V6
Outline the areas of the heart which groups of ECG leads cover
What proportion of iindividuals have a posterior descending artery which is an extention of the left circumflex artery rather than from the RCA?
10%
What might an inferolateral MI indicate?
Left dominant coronary circulation
What occurs on ECG occurs when the following happens?
In Isolation or together
- ST depression
- T-wave inversion
Can also have
- Hyperacute T-waves
- U-wave inversion
Why do Q-waves not occur in NSTEMI?
No window is created by dead area of tissue, meaning that the opposite wall isn’t seen on ECG
Can NSTEMI and unstable angina be distinguished by ECG alone?
No - need troponin to determine if cardiac necrosis has occured
What are the different morphologies of ST depression?
- Horizontal
- Upsloping
- Downsloping
