ECG 2: Beyond the Basics

Question 1

What is the axis?

Answer 1

the “average” vector direction

Question 2

Which leads are in the coronal plane?

Answer 2

I, II, III

aVR, aVL, aVF

Question 3

If all the coronal-plane leads are arranged together coming from one 0 point, how are they arranged?

Answer 3

Roughly in a circle, with 30 degrees between each lead

Question 4

Which lead is defined as 0 degrees?

Answer 4

Lead I

points straight to pt’s left

Question 5

Are the leads defined in a clockwise or counterclockwise way?

Answer 5

Clockwise
eg aVF is +90 degrees
aVL is -30 degrees

Question 6

What is the isoelectric lead?

Answer 6

Lead that is not positive or negative, but has equal amt of upward and downward deflection

important

Question 7

What is a shortcut for left axis deviation?

Answer 7

Up in I and down in II

Question 8

What is a shortcut for right axis deviation?

Answer 8

Down in I and up in aVF

Question 9

What does the normal axis look like?

Answer 9

Upgoing QRS in both I and II

Question 10

How is the extreme axis defined?

Answer 10

Down in I and down in aVF

Question 11

How can you use an isoelectric lead to define axis?

Answer 11

• 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!]

Question 12

How do you determine which direction is greater, in a lead that is both + and - ?

Answer 12

Area under the curve: more area under + or - side

Question 13

Which 3 leads are used to define axis?

Answer 13

I, II, and aVF

Question 14

How do you use leads to define axis?

Answer 14

• 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!

Question 15

What are the main axis categories? Define their range (in degrees)

Answer 15

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

Question 16

Which bundle depolarizes the septum?

Answer 16

Left bundle

Question 17

Which is depolarized first, endocardium or epicardium?

Answer 17

Endocardium: fibres are near the endocardium, and the wave travels out from there

Question 18

If a bundle branch is blocked, what happens?

Answer 18

Opposite ventricle depolarizes first

Question 19

What do abnormalities of repolarization cause on ECG?

Answer 19

Changes in the ST segment

Question 20

If you see ST changes, what should you think of?

Answer 20

MI or ischemia

But before diagnosing, always consider other things that can cause ST changes! Always do your full 12 lead interpretation.

Question 21

What leads are particularly important for assessing LBBB?

Answer 21

V1 and V6 (anterior and lateral)

Question 22

What happens in the heart with LBBB?

Answer 22

Fast RV depolarization followed by slow late LV depolarization

Question 23

If a small upgoing deflection is seen in V1, what does that reflect?

Answer 23

RV depolarization

Question 24

What does slow late LV depolarization show as in V1?

Answer 24

Large wide negative deflection

Question 25

What does slow late LV depolarization show as in V6?

Answer 25

Large wide positive deflection

Question 26

What is the intrinsicoid deflection?

Answer 26

Time from start of QRS to peak of R wave Also called the R peak time

Question 27

What is the LBBB criterion for intrinsicoid deflection?

Answer 27

> 60 ms ( = 1.5 little boxes)

Question 28

What happens to the wave of repolarization in BBB?

Answer 28

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

Question 29

What is discordance?

Answer 29

When the T wave is in the opposite direction of the QRS

Question 30

What are the diagnostic criteria for LBBB?

Answer 30

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)

Question 31

Name 2 exceptions to LBBB Dx criteria

Answer 31

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).

Question 32

What are the QRS width criteria for LBBB in children

Answer 32

> 100 ms in ages 4-16 | > 90 ms in ages < 4 yrs

Question 33

Name 3 important ways RBBB is different from LBBB

Answer 33

- 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

Question 34

What are the diagnostic criteria for RBBB?

Answer 34

QRS > 120 ms RSR' configuration in V1/2 slurred (wide) S wave in V5/6

Question 35

What happens in the heart with RBBB?

Answer 35

- septum depolarizes early and quickly - LV depolarizes quickly - RV depolarizes slowly

Question 36

How does septum depolarization show on ECG in RBBB?

Answer 36

Early upgoing R wave in V1/V2 | Might produce a small downgoing (Q wave) in V6

Question 37

How does LV depolarization show on ECG in RBBB?

Answer 37

downward deflection (S wave) in V1/V2 and an upward deflection (R wave) in V6

Question 38

How does RV depolarization show on ECG in RBBB?

Answer 38

Produces a second upward deflection in V1/V2 We call this waveform R prime (R') V6: wide downgoing waveform, called a "slurred" S wave

Question 39

What is the shape of the QRS complex in V1/2 in RBBB?

Answer 39

RSR' configuration RaBBBit ears

Question 40

What is a slurred S wave?

Answer 40

Result of slow late RV depolarization wider that the R wave or > 40 ms (1 little square) Wide with rounded, not pointy, bottom

Question 41

Is the intrinsicoid deflection narrow or wide in RBBB?

Answer 41

Narrow (normal): reflects normal LV depolarization

Question 42

What do lower case letters in QRS indicate?

Answer 42

Relative wave size eg rSR': the second R wave is larger than the first R wave

Question 43

When might the first R wave be missing in RBBB?

Answer 43

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

Question 44

What are the diagnostic criteria for incomplete BBB?

Answer 44

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)

Question 45

What it intraventricular delay?

Answer 45

``` 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

Question 46

What is Brugada syndrome?

Answer 46

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 ```

Question 47

What is ventriculophasic sinus arrythmia?

Answer 47

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.