Intro to ECG Part 2: 12 Lead ECG

Question 1

Question 2

The 2 leads that show normal P waves the best are :

Answer 2

The 2 leads that show normal P waves the best are lead II (downward and to the left) and V1 (anterior):

Question 3

When there are more P waves:

When there are more QRS’s:

Answer 3

When there are more P waves:

some P waves are not getting conducted to the ventricles due to conduction block in the AV node (AV node cant get the SA node signal)

When there are more QRS’s:

a QRS is being generated but no P wave is being generated

this occurs when the AV node or the ventricles generate the QRS

Question 4

what might be happening?

Answer 4

Crazy, all those P waves! Did you count 16? And only 4 QRS’s so there is a conduction block (in the AV node).

Question 5

Whats going on with the P:QRS ratio?

Answer 5

Question 6

Answer 6

The first and 3rd P waves are the same. All others are different. Therefore, there are multiple origins for the P waves.

One detail that might be helpful for you: P waves almost always will have a regular rhythm if they are from the same source. Therefore, an early beat among many regular beats is most likely (> 99% of the time), arising from a different location and as such, will likely have a different size and shape.

Question 7

Super important causes of slow conduction (wide QRS):

Answer 7

=conduction from ventricular myocyte to myocyte is much slower compared to the purkinje fibers. This happens when an electrical signal STARTS in the ventricle muscle.

= diseased conducting fibers, typically called conduction delay, aberrancy, or bundle branch block.

Question 8

what is a bundle branch block?

Answer 8

In brief, with bundle branch block one of the bundle branches is not conducting. Therefore, the electrical signal moves quickly down from the AV node through one bundle branch, but to get to the other side of the heart, the signal must be conducted from myocyte to myocyte, which is slow conduction. This requires extra time and causes the QRS to be wide.

Question 10

normal axis is indicated by a postive lead in ___ and ___

Answer 10

lead I and II

Question 11

which precordial lead measures RV? which one measures LV?

Answer 11

V1-V3 more likely to measure RV because RV is more anterior. V6 likely to measure LV because it’s more lateral.

Question 12

In LBBB what would the precordial leads look like

Answer 12

V1= small and fast initial upward signal (this is the RV monitor so it’s not super affected)

V6 = wide and slow because there’s a block in LV.

Question 13

if there is an LBB, the T waves will be ___ from the QRS

Answer 13

it will be discordant from the QRS. Going in opposite directions.

Question 14

Answer 14

Question 15

T/F; when you have LBBB, the ST segment is
not useful for ischemia diagnosis

Answer 15

true. In LBB, the QRS and T complexes are abnormal (wide, discordant) Because all aspects are abnomrla, the ST segment is also abnormal and it will be difficult to know if the ST change is due to LBBB or ischemia.

Question 16

in RBBB, there is early and fast depolarization of the ____. but slow and wide ____ depolarization.

Answer 16

in RBBB, there is early and fast depolarization of the SEPTUM. but slow and wide VENTRICLE depolarization.

Question 18

common causes of left ventricular hypertrophy

Answer 18

hypertension and aortic valve stenosis. these cause increased afterload and the LV gets larger.

Question 19

findings on ecg that indicate left ventricular hypertrophy

Answer 19

wider and taller QRS.

abnormal depolarization = abnormal repolarization therefor also have abnoraml ST segment and T wave.

Question 20

in left ventricular hypertrophy, which precordial lead will be most affected?

Answer 20

V6 will have tall upgoing V6 signals.

V1 and V2 will have deep downgoing signals but won’t be as “tall” as V6

Question 22

Sokolow and Lyons Criteria for Left Ventricular Hypertrophy

Answer 22

take deepest in V1 or V2 and tallest in V5 or V6, it should be more than 35 mm

Question 23

outline the Avl criteria for left ventricular hypertrophy

Answer 23

AvL should be over 11mm

Question 24

The following characteristics are typical of LEFT VENTRICULAR HEART FAILURE
repolarization abnormalities:
– ST segment ___ if QRS is downgoing
– ST segment ____ if QRS is upgoing
– Magnitude of elevation/depression is proportional
to the size of the QRS

– ST is “scooped” concave up with elevation

– ST is scooped concave down with depression

Answer 24

The following characteristics are typical of LVH
repolarization abnormalities:
– ST segment elevation if QRS is downgoing
– ST segment depression if QRS is upgoing
– Magnitude of elevation/depression is proportional
to the size of the QRS

– ST is “scooped” concave up with elevation

– ST is scooped concave down with depression

Question 25

Infarct/Ischemia Changes seen: 1. Peaked or **\_\_** T waves 2. ST **\_\_** (ischemia) 3. ST **\_\_** (infarction) 4. Deep __ waves (late or old infarct) 5. Poor R wave progression

Answer 25

1. Peaked or inverted T waves 2. ST **depression** (ischemia) 3. ST **elevation** (infarction) 4. Deep **Q** waves (late or old infarct) 5. Poor R wave progression

Question 26

what is the j point on an ECG

Answer 26

the point where the QRS and ST segment joint. A j point can be elevated, depressed, slurred or notched.

Question 27

is J point elevated or depressed?

Answer 27

elevated

Question 28

characterize the J point

Answer 28

depressed

Question 29

characterize the J point

Answer 29

J point is notched

Question 30

Question 31

outline these QRS waves

Answer 31

in an infarction, the R wave gets driven down to the point it becomes a "pathological Q wave"

Question 32

Question 34

What changes in V1 would you expect in left atrial enlargement?

Answer 34

with LAE, the P wave in V1 will be initially upgoing for the first portion (red arrow below) and then downgoing in the terminal portion (blue arrow). This is called biphasic. The green arrow points to the QRS. The T wave is not seen in this image.

Question 35

what changes in lead II would you see in left atrial enlargement?

Answer 35

When the LA enlarges, wave of depolarization measured in lead II behaves like 2 separate waves. The first one is the right atrium and the second one is the left atrium. The 2 waves partly overlap each other, so it creates an **M shaped P wave in lead II. This is also called a notched P wave**. In the diagram below, there is an extra blue and red fuzzy line to show the 2 different atrial waves:

Question 36

overall diagnostic criteria for left atrial enlargement

Answer 36

think about lead placement and think about how many more cells are in the atria if it's enlarged, therefore it would take longer for the signal to get through. ## Footnote **Summary of Diagnostic Criteria for LAE:** **wide P wave \> 120 ms** **M shaped P wave in lead II** **biphasic P wave in lead V1 (initally upward, terminal portion downward)** **terminal portion of V1 is at least 1 little square wide**

Question 38

Best leads to see right atrial enlargements

Answer 38

leads II and V1. also good leads to see left atrial enlargement. it's cause it shows the P waves th ebest

Question 39

diagnostic finding of RAE

Answer 39

when the right atrium enlarges, the electrical signal becomes stronger in the direction of the axis of lead II. - as a result, the P wave in lead II is taller. A P wave that is \>2.5 mm in lead II is diagnostic of RAE.

Question 40

The enlarged RA will also create a stronger electrical signal toward\_\_as seen in the diagram. This will result in a taller P wave in\_\_\_, but only for the first half of the P wave.

Answer 40

The enlarged RA will also create a stronger electrical signal **toward V1** as seen in the diagram. This will result in a taller P **wave in V1,** but only for the first half of the P wave.

Question 41

compare P wave duration between LAE and RAE

Answer 41

In contrast to LEFT atrial enlargment, **the P wave duration is normal (\< 120 ms or 3 little squares) with RAE**. Check the ECG above to see that even though there is a biphasic P wave in V1 (suggesting LAE), the P wave width is \< 120

Question 42

overall diagnostic criteria for RAE

Answer 42

P wave taller than 2.5 mm in **lead II** P wave is usually pointy (P wave taller than 1.5 mm in **lead V1)** (P wave duration \< 120 ms)

Question 43

Note about left VENTRICLE hypertrophy: To simplify, all criteria measure the height or depth of the QRS and if these values are big, then LVH is diagnosed. The differences between all the different diagnostic criteria are the selection of ECG leads and the value that is selected. The electrical vector for the LV (yellow arrows) travels mostly AWAY from V1,2 and mostly TOWARD V5,6:

Question 44

Remember that depolarization away from a lead will cause a negative deflection (\_\_ wave) and toward a lead will cause a positive deflection (\_\_ wave).

Answer 44

Remember that depolarization away from a lead will cause a **negative deflection (S wave) and toward a lead will cause a positive deflection (R wave)**.

Question 45

In LVH, the\_\_\_ waves in V1/2 and\_\_\_ waves in V5/6 are amplified. We measure them to see exactly how amplified they are

Answer 45

In LVH, t**he S waves in V1/2 and R waves in V5/6 are amplified.** We measure them to see exactly how amplified they are. Here are examples of a deep S wave in V2 and a tall R wave in V6:

Question 46

sokolow and lyos criteria for left ventricular hypertrophy

Answer 46

Question 47

cornell criteria for LVH

Answer 47

Question 48

aVL criteria for left ventricular hypertrophy.

Answer 48

Question 49

3 features of St-T wave abnormalities that are secondary to left ventricular hypertrophy

Answer 49

1. the ST segment depression/elevation will typically be in the opposite direction to the qrs. 2. the magnitude of ST changes will be proportional to the size of the QRS. Really tall or deep QRS's will be associated with greater amounts of ST segment depression or elevation. 3. the ST segment will be concave away from the QRS.

Question 50

ST changes in LVH vs Ischemia or infarction.

Answer 50

With **myocardial ischemia or infarction:** ST segments will be **flat(ter) and not concave** ST elevation or depression is **not related to the direction of the QRS-- ex/ a positive QRS may elicit a positive st elevation in ischemia. but a positive QRS would elicit an ST depression in left ventricular hypertrophy.** ST elevation or depression magnitude **is not proportional to the magnitidue of the QRS- a small QRS might still have a huge ST elevation following it.**

Question 51

Question 52

Summary of diagnostic criteria that SUGGEST the presence of RVH:

Answer 52

tall upgoing R wave in V1 \> 6 mm R:S ratio \> 1 in V1 R:S ratio \< 1 in V6 right axis deviation (RAD) right atrial enlargement (RAE)