Diagnostic Features of ECG

Question 1

There are 5 heavy lines between 2 different QRS’s. What is the heart rate?

Answer 1

300/5=60.

For heavy lines the equation is 300/# of heavy lines

Question 2

There are 20 thin lines on an ECG between 2 QRS waves. What is the heart rate?

Answer 2

The heart rate is 1500/20=75.

For the thin lines, the equation is 1500/thin lines.

Question 3

T or F?

A repolarization moving toward a positive electrode produces a positive deflection

Answer 3

False.

a DEPOLARIZATION moving toward a positive electrode produces a positive deflection

Question 4

In which direction does a depolarization travel in relation to the heart?

Answer 4

It moves from right to left in a downwards motion toward the apex of the heart.

Question 5

I have a lead placed at the base of the heart. In which direction will the QRS wave deflect on this lead?

Answer 5

negative (downward). The QRS travels in the direction of base to apex of the heart, so it would be moving away from the lead, thus resulting in a negative deflection.

Question 6

How many total limb leads are there? How are they distinguished?

Answer 6

There are 6 total limb leads.

3 of them are bipolar leads (I,II,III) which are the standard leads.

3 of them are unipolar leads (aVR, aVL, aVF), and these are augmented limb leads.

Question 7

T or F

There are 6 bipolar precordial leads

Answer 7

False.

There are 6 unipolar precordial leads (V1-V6)

So there are 6 total limb leads (3 bipolar, 3 unipolar) and 6 total precordial leads (all unipolar)

Question 8

Which forces are readily detected by the bipolar limb leads?

Answer 8

Downward forces because both of the leads are positive down there. They would be good at detecting a change in the inferior wall of the heart (See image)

Question 9

What’s a good conceptual way to remember where AVR, AVL, and AVF are located?

Answer 9

AVR=right arm (R for right)

AVL=left arm (L for left)

AVF=left foot (F for foot)

see image

Question 10

Which leads are considered inferior?

Which leads are considered lateral?

Answer 10

Inferior=AVF, II, III

Lateral=AVL, I

see image

Question 11

Which precordial leads are considered right sided leads?

What about left sided?

Answer 11

Right sided=V1 and V2 (these can also detect septal infarcts)

Left sided=V5 and V6

Question 12

What would you expect to see on an ECG in left ventricular hypertrophy compared to normal? Why?

Answer 12

You should see a larger R wave on the left sided leads (AVL, I, V5, V6).

This is because with more muscle there is greater voltage, resulting in increased amplitude.

Question 13

A patient comes in with right ventricular hypertrophy. What would you expect to see on the ECG?

Answer 13

You should see a larger R wave on the right sided leads V1 and V2 (which is normally hard to see).

Question 14

What are the 3 conditions in relation to the coronary artery that can be picked up by ECG?

Answer 14

Ischemia, Injury, and Infarct.

Question 15

What are the 2 forms of ischemia and what effect do they have on the ECG?

Answer 15

1) Ischemia due to sudden high oxygen demand (ie exercise) with fixed coronary obstruction. Causes a depression of the ST segment (which is normally isoelectric).
2) Ischemia due to acute coronary obstruction during low oxygen demand. Causes a T wave inversion (T wave opposite direction of QRS wave)

Question 16

You look at an ECG and suspect someone to have some sort of myocardial injury. What ECG finding would make you expect this?

Answer 16

ST elevation

Question 17

T or F?

Both Ischemia due to exercise and Injury will show ST elevation as a sign on ECG.

Answer 17

False.

Ischemia will have ST depression, injury will show ST elevation.

Question 18

T or F?

A transmural infarct produces Q waves.

Answer 18

True

Question 19

What’s the difference between elevated ST waves and a present Q wave in regards to transmural infarct?

Answer 19

ST wave may be reversible.

Q wave isn’t reversible, it represents necrosis.

Question 20

List the 3 criteria for establishing a Q wave as significant

Answer 20

1) the wave is at least 1/4 the amplitude of the R wave
2) the wave is at least .04 seconds wide (at least one little box on the ECG)
3) At least 2 leads detect the same Q wave in the same area of the left ventricle (Most important!)

Question 21

What is the most common type of infarct and what does that mean?

Answer 21

Transmural infarct.

This means that the entire portion of the ventricle is blocked (all the way through the wall, from the ventricle out to the outside of the heart in that portion of the heart)

Question 22

How do the findings of a transmural and a subendocardial infarct differ on ECG findings?

Answer 22

Transmural: Elevated ST, significant Q wave.

Subendocardial: ST depression, no Q wave. (this one looks just like an exercise ischemia)

Question 23

Name which area of the heart each group of leads looks at:

V1/V2

V3/V4

V5/V6

II,III, AVF

I, AVL

Answer 23

V1/V2=Anteroseptal wall

V3/V4=Anterior wall

V5/V6=Anterolateral wall

II,III,AVF=Inferior wall

I,AVL=High lateral wall

Question 24

Generally, which is larger and more serious, an anterior or inferior infarct?

Answer 24

Anterior infarcts are generally larger and more serious.

Question 25

If the QT interval is more than half of the R-R interval, what does that mean?

Answer 25

It means you have a prolonged QT interval.

This is a major risk factor for arrythmias.

Causes: electrolyte imbalances, anti-arrhythmatic drugs, Hypothermia, Congenital