S6L1 - Interpreting ECGs

Question 1

Define depolarisation

Answer 1

Change within cell of electrical charge distribution leading to a less negative charge within the cell

Question 2

Define Repolarisation

Answer 2

Change within the cell of electric charge distribution leading to more negative charge inside the cell.

Question 3

Define resting membrane potential

Answer 3

Electrical imbalance between the inside and outside of the cell due to separation of charges across the cell membrane. Measure in mV

Question 4

What is the function of specialised myocytes?

Answer 4

These are pacemaker cells, and have an intrinsic rhythm. Set the cardiac rate and rhythm by spontaneously generating AP that initiate the cardiac cycle.

Question 5

Where are the primary pacemaker cells located?

Answer 5

In the sinoatrial node. Where the superior veins Cavan empties into the right atrium.

Question 6

How are cardiac cells electrically connected?

Answer 6

Through gap junctions. Allows unidirectional propagation of action potential.

Question 7

What is excitation-contraction coupling?

Answer 7

Depolarisation wave causing coordinated contraction of the atria and ventricles

Question 8

Where is the atrioventricular node located?

Answer 8

In the inter-atrial septum near the tricuspid valve (bottom left of right atrium)

Question 9

What happens at the AV node?

Answer 9

Impulse is delayed by 120-200ms in order to delay ventricular contraction.

Question 10

What is the bundle of his?

Answer 10

Fast conducting electrical fibres that start in the atria, goes through the annulus fibrosus and travels down the ventricles through the septum.

Question 11

What is the annulus fibrosis?

Answer 11

The fibrous skeleton of the heart that anchors the myocardium and cardiac vessels. It is an electrical insulator between the atria and the ventricles. Consists of 4 fibrous rings.

Question 12

What does the bundle of his divide into?

Answer 12

The righ bundle branch and the left bundle branch within the interventricular septum.

Question 13

Where does the RBB and the LBB terminate?

Answer 13

Terminate at the apex of the heart into the purkinje fibres which continue t conduct the depolarisation wave through the ventricles up to the base of the ventricles.

Question 14

What is the difference between a wave and a deflection?

Answer 14

A wave has one deflection, a complex has more than one

Question 15

What is the function of the right leg electrode?

Answer 15

The grounding electrode. Does not contribute to any views of the heart.

Question 16

How many electrode are there?

Answer 16

10
4 on limbs
6 on chest

Question 17

How many leads are there?

Answer 17

12 leads.

Question 18

Describe the classic limb leads 1, 2 and 3

Answer 18

Bipolar, have negative and positive electrodes.

Question 19

Describe limb lead 1

Answer 19

Voltage difference between the electrode on the RA and LA. LA is positive electrode.

Question 20

Describe limb lead 2

Answer 20

Voltage difference between electrode RA and LL. LL is positive electrode

Question 21

Describe limb lead 3

Answer 21

Voltage difference between the LA and LL electrodes. LL is positive electrode.

Question 22

What are augmented limb leads?

Answer 22

Uni polar - only have a positive electrode
AVL = left arm
AVR = right arm 
AVF = left leg.
Use same electrodes as limb leads.

Question 23

How are limb leads viewed?

Answer 23

Limb leads are viewed from positive to negative

Question 24

Describe the function of the precordial chest leads

Answer 24

Have horizontal views of the heart. Are unipolar.

Question 25

What does the p wave represent?

Answer 25

Represents the depolarisation of the atria. Upwards deflection from lead 2 as depolarisation is travelling towards the LL electrode.

Question 26

What is represented by the R wave?

Answer 26

A upwards