ECG 2: Beyond the Basics Flashcards
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?
Lead I
points straight to pt’s left
Are the leads defined in a clockwise or counterclockwise way?
Clockwise
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
important
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?
Left bundle
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?
RV depolarization
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
What are the diagnostic criteria for LBBB?
Summary of Diagnostic criteria for LBBB:
- QRS > 120 ms
- V6: broad (wide) R wave (upgoing wave) (also in leads I, aVL and V5)
- V1: small R wave, big S wave (also called rS)
- QRS and T waves are in opposite directions (discordance) in most/all of the precordial leads
- (optional but not required) V6: intrinsicoid deflection > 60 ms
- (notice there are no Q waves in precordial leads)
Name 2 exceptions to LBBB Dx criteria
sometimes the QRS and T waves can both be upgoing (“positive” concordance). However, they cannot both be downgoing (“negative” concordance)
sometimes there is an R + S wave in V6 instead of just an R wave. Late LV depolarization AWAY from V6 causes the S wave (see image).
What are the QRS width criteria for LBBB in children
> 100 ms in ages 4-16
> 90 ms in ages < 4 yrs
Name 3 important ways RBBB is different from LBBB
- common in normal healthy adults
- does not cause big changes in ST or T wave (bc LV is functioning normally)
- thus does not cause Dx interference with MI, ischemia, or LVH
What are the diagnostic criteria for RBBB?
QRS > 120 ms
RSR’ configuration in V1/2
slurred (wide) S wave in V5/6
What happens in the heart with RBBB?
- septum depolarizes early and quickly
- LV depolarizes quickly
- RV depolarizes slowly
How does septum depolarization show on ECG in RBBB?
Early upgoing R wave in V1/V2
Might produce a small downgoing (Q wave) in V6
How does LV depolarization show on ECG in RBBB?
downward deflection (S wave) in V1/V2 and an upward deflection (R wave) in V6
How does RV depolarization show on ECG in RBBB?
Produces a second upward deflection in V1/V2
We call this waveform R prime (R’)
V6: wide downgoing waveform, called a “slurred” S wave
What is the shape of the QRS complex in V1/2 in RBBB?
RSR’ configuration
RaBBBit ears
What is a slurred S wave?
Result of slow late RV depolarization
wider that the R wave or > 40 ms (1 little square)
Wide with rounded, not pointy, bottom
Is the intrinsicoid deflection narrow or wide in RBBB?
Narrow (normal): reflects normal LV depolarization
What do lower case letters in QRS indicate?
Relative wave size
eg rSR’: the second R wave is larger than the first R wave
When might the first R wave be missing in RBBB?
if the patient has had an old anterior infarct with Q waves
First R wave in V1/2 might be missing because the R wave is replaced by a Q wave
What are the diagnostic criteria for incomplete BBB?
essentially share the same diagnostic criteria as complete bundle branch blocks with one difference: the QRS duration is shorter with incomplete blocks
QRS duration diagnostic criteria for incomplete bundle branch blocks is 100 - 120 ms (which is 2.5 - 3 little squares)
What it intraventricular delay?
wide QRS (QRS > 120 ms) Does not meet the criteria for LBBB or RBBB
not diagnosed if the rhythm has a ventricular origin, such as VT
What is Brugada syndrome?
can mimic or be associated with RBBB; caused by Na+ or Ca++ channel mutation
Diagnostic criteria:
- J point elevation with ST elevation in V1-V3
- the ST is described as coved or saddlebacked
coved = downsloping and convex upward saddlebacked = flat ST elevation with initial and final parts of ST segment slightly higher
What is ventriculophasic sinus arrythmia?
non-respiratory sinus arrhythmia seen in complete AV block.
The PP interval enclosing a QRS complex is shorter than a PP interval not enclosing a QRS.
