Flashcards in ECG 2: Beyond the Basics Deck (47)
What is the axis?
the "average" vector direction
Which leads are in the coronal plane?
I, II, III
aVR, aVL, aVF
If all the coronal-plane leads are arranged together coming from one 0 point, how are they arranged?
Roughly in a circle, with 30 degrees between each lead
Which lead is defined as 0 degrees?
points straight to pt's left
Are the leads defined in a clockwise or counterclockwise way?
eg aVF is +90 degrees
aVL is -30 degrees
What is the isoelectric lead?
Lead that is not positive or negative, but has equal amt of upward and downward deflection
What is a shortcut for left axis deviation?
Up in I and down in II
What is a shortcut for right axis deviation?
Down in I and up in aVF
What does the normal axis look like?
Upgoing QRS in both I and II
How is the extreme axis defined?
Down in I and down in aVF
How can you use an isoelectric lead to define axis?
- find which lead is the most isoelectric
- the axis is along that lead's line
- use the other activity (eg upgoing in I and II) to define which "quadrant" it's in (eg the +60 vs the -120 end of the line)
[This is lesson 4 of Axis module if you want to review!]
How do you determine which direction is greater, in a lead that is both + and - ?
Area under the curve: more area under + or - side
Which 3 leads are used to define axis?
I, II, and aVF
How do you use leads to define axis?
- draw the 3 leads as arrows
- look at each lead to see if it is positive or negative
- shade in the relevant (+ or -) semicircle for that lead (at right angle to direction of the lead)
- see where they overlap!
What are the main axis categories? Define their range (in degrees)
Normal: -30 to + 90 degrees
Right axis deviation: +90 to +180 degrees
Left axis deviation: -30 to -90 degrees
Extreme axis deviation: -90 to -180 degrees
Which bundle depolarizes the septum?
Which is depolarized first, endocardium or epicardium?
Endocardium: fibres are near the endocardium, and the wave travels out from there
If a bundle branch is blocked, what happens?
Opposite ventricle depolarizes first
What do abnormalities of repolarization cause on ECG?
Changes in the ST segment
If you see ST changes, what should you think of?
MI or ischemia
But before diagnosing, always consider other things that can cause ST changes! Always do your full 12 lead interpretation.
What leads are particularly important for assessing LBBB?
V1 and V6 (anterior and lateral)
What happens in the heart with LBBB?
Fast RV depolarization followed by slow late LV depolarization
If a small upgoing deflection is seen in V1, what does that reflect?
What does slow late LV depolarization show as in V1?
Large wide negative deflection
What does slow late LV depolarization show as in V6?
Large wide positive deflection
What is the intrinsicoid deflection?
Time from start of QRS to peak of R wave
Also called the R peak time
What is the LBBB criterion for intrinsicoid deflection?
> 60 ms ( = 1.5 little boxes)
What happens to the wave of repolarization in BBB?
Normal pattern is lost: repolarization goes from inside to outside (instead of outside to inside)
Thus, T wave is in the opposite direction of the QRS
What is discordance?
When the T wave is in the opposite direction of the QRS