Physiology - ECG

Question 1

Name the charges inside/outside the heart at the different phases of AP conductance.

Answer 1

RMP: negatively charged inside, positively charged outside
Atrial depolarization: positive inside, negative outside
Ventricular depolarization: positive inside, negative outside
Ventricular repolarization: negative inside, positive outside

Question 2

Where does depolarization travel?

Answer 2

Towards the positive electrode: positive potential (upwards)
Depolarization away from the positive electrode: negative potential (downwards)
Repolarization away from the positive electrode: positive potential (upwards)

Question 3

What does the isoelectric line show?

Answer 3

No depolarization/repolarization - no potential difference

Question 4

Where are the standard limb leads placed? (I, II, III)

Answer 4

Left arm (LA)
Right arm (LA)
Left leg (LL) 
Earth placed on right leg

Question 5

What forms the triangle in the original system?

Answer 5

Right shoulder
Left shoulder
Pubic area
= Einthoven triangle

Question 6

What makes up the ECG?

Answer 6

Waves - P,Q, R, S, T

Segments - distances between waves

Question 7

What do intervals comprise of?

Answer 7

Both waves and segments

Question 8

What is a combination of 2 electrodes called?

Answer 8

A bipolar lead

Question 9

What does lead I record?

Answer 9

Potential difference between LA and RA (LA is positive, RA is negative)

Question 10

What does lead II record?

Answer 10

Potential difference between LL and RA

LL is positive, RA is negative

Question 11

What does lead III record?

Answer 11

Potential difference between LA and LL

LL is positive, LA is negative

Question 12

What are augmented limb leads?

Answer 12

Three new limb leads - unipolar (one electrode positive, other two negative).
aVR, aVL, AVF
The main deflection is positive for all leads except aVR