Electrocardiogram PQRS

Question 1

What happens at P wave?
Positive or negative deflection?

Answer 1

atrial depolarization - positive deflection
line goes up

Question 2

What happens at Q wave?
Positive or negative deflection?

Answer 2

First negative/downward deflection before R wave

Question 3

What happens at R wave?
Positive or negative deflection?

Answer 3

First positive deflection of QRS
start of ventricular depolarization

Question 4

What happens at S?
Positive or negative deflection?

Answer 4

Negative/downward deflection after an R Wave
ventricle contracts after QRS

Question 5

What happens at T wave? positive or negative deflection?

Answer 5

Ventricular repolarization
First major deflection/bump after QRS

Question 6

Label the entire ECG of a heartbeat

Answer 6

1. P
2. R
3. T
4. PR interval
5. PR segment
6. Q
7. S
8. QRS interval
9. ST segment
10. QT interval

Question 7

What is Ta wave? Positive or negative deflection? Why is it rarely seen?

Answer 7

It is atrial repolarization
not seen because low volt
down or opposite P wave
seen in 3rd degree AV block

Question 8

What is the PR interval? What should it be called?
If this interval is prolonged what does it represent?

Answer 8

• start of P wave to first deflection of QRS complex
  (should be called PQ interval)
• prolonged = atrial enlargement or AV conduction problem

Question 9

What is the qRs complex?
What does Q, R, and S represent individually?

Answer 9

ventricular depolarization
- Q = first negative deflection preceding R wave
- R = first positive deflection
- S = first negative deflection proceeding after R wave

Question 10

Label the electrical prorogation compared to heart anatomy

Answer 10

1 = SA node
2 = atrial depolarization
3 = AV node
4 = His bundle
5 = left/right bundle branches
6 = Purkinje fibers
7 = ventricular depolarization

Question 11

What is the ST segment?
What is its electrical voltage?

Answer 11

end of QRS to T wave
isoelectric – if increased/decreased
means myocardial ischemia

Question 12

What is special about T wave?

Answer 12

ventricular repolarization

Question 13

What is the QT interval? What does it measure?

Answer 13

start of QRS complex to end of T wave =
ventricular depolarization & repolarization

Question 14

How can we calculate a heart rate independent index? (QTc)

Question 15

Can we alter the duration of the QT interval?

Answer 15

YES - with sympathetic tone and prolonged or decreased Ca+2 entry into cell

Question 16

When does the wave of depolarization reach the AV node on the ECG?

Answer 16

1/2 way through P wave

Question 17

Describe priming the pump and its purpose

Answer 17

electrical activity of atria induces mechanical activity throwing about 10-15% of bld into right ventricle during depolarization

Question 18

How does depolarization move through the myocardium in category A animals?
Where is the terminal wave?

Answer 18

endocardium to epicardium
- terminal wave = ventricular septum

Question 19

What are Category A animals? Give example

Answer 19

• purkinje fibers on endocardial surface
• ex) dogs, cat, human, rat

Question 20

What are category B animals?
How does this alter the depolarization movement?
give example

Answer 20

• purkinje fibers diffuse throughout the myocardium
• depolarization is simultaneous throughout ventricular myocardium
  (bigger muscle takes longer to depolarize = needs to be simultaneous)
• ex) horse, cow, sheep, goat, whale

Question 21

When is the base-apex lead used?
What does it provide?

Answer 21

category B animals
provides greatest amplitude for P, QRS, and T wave

Question 22

What can frontal bipolar/unipolar leads not detect in category B animals?

Answer 22

chamber enlargement

Question 23

Where is the negative and positive terminal of the base-apex lead?

Answer 23

neg = right jugular vein furrow
pos = left thorax over apex beat

Question 24

Label Category B ECG

• compare to lead II ECG

Answer 24

1 = PR interval 2 = PR segment
3 = QT interval 4 = ST segment
5 = TQ interval 6 = T wave
7 = rS complex 8 = r
9 = P wave 10 = S

Question 25

How are small animals placed for ECG compared to LA?
Why?

Answer 25

small animals = right lateral recumbency
large animals = standing (less muscle tremor artifact on large animals)

Question 26

What 4 features do we examine on an ECG?

Answer 26

1. heart rate (atrial rate, ventricular rate)
2. heart rhythm
3. P-QRS-T complexes and intervals
4. mean electrical axis in frontal plane (Category A only)

Question 27

What is the R-R interval? What is it measuring?

Question 28

What is the P-P interval? what is it measruing?

Question 29

What can the mean electrical axis demonstrate?

Question 30

What does a right shift indicate for the mean electrical axis?
Why?

Answer 30