lecture 8 : electrocardiography 1

Question 1

what is a vector?

Answer 1

a quantity that has both magnitude and direction

Question 2

what does the ECG show?

Answer 2

an isoelectric line

Question 3

what are the two things required for an ECG?

Answer 3

an anode and a cathode

Question 4

what is shown through a current towards the positive electrode?

Answer 4

positive deflection on the ECG

Question 5

what is shown through a current away from the positive electrode?

Answer 5

a negative deflection

Question 6

* draw a basic diagram of a PQRST wave

Answer 6

insert pic

Question 7

* show the shape of the sinoatrial node wave? and what happens?

Answer 7

insert pic - auto rhythmic myocytes - atrial depolarisation

Question 8

* show the shape of the atrial ventricular node

Answer 8

insert pic - the AV node is slowing the conduction - protective

Question 9

* show the shape of the bundle of his

Answer 9

insert pic - rapid conduction due to being insulated

Question 10

* show the shape of the bundle branches

Answer 10

insert pic septal depolarisation

Question 11

* show the shape of the purkinje fibres

Answer 11

insert pic - ventricular depolarisation - main event - massive spike

Question 12

* show the shape of the purkinje fibres 2

Answer 12

insert pic - the depolarisation goes up both the sides of the ventricles - but the left ventricle has more muscle therefore there is a greater spike

Question 13

* show the shape of the fully depolarised ventricles

Answer 13

insert pic isoelectric ECG

Question 14

* show the shape of repolarisation?

Answer 14

insert pic - this is the ventricular repolarisation

Question 15

* what is lead 1 ?

Answer 15

• this is detecting a depolarisation current from the right arm to the left arm insert pic

Question 16

* what is lead 2?

Answer 16

• this is detecting a depolarisation current from the right arm to the left leg insert pic

Question 17

what is lead 3?

Answer 17

• this is detecting a depolarisation current from the left arm to the left leg insert pic

Question 18

how do you take augmented leads? what are the leads?

Answer 18

• this includes aVR aVL aVF - they are obtained using the average voltage of any two points on the skin as a negative pole and the third reading from a positive electrode

Question 19

* whats the lead aVR?

Answer 19

• it is from the mid point of the left arm and the left leg - flows to the positive right arm electrode - this displays as a negative on the ECG insert pic

Question 20

* whats the lead aVL?

Answer 20

• this is from the mid point of the right arm and the left leg and flows to the positive left arm electrode - this shows as positive on the ECG insert pic

Question 21

* whats the lead aVF?

Answer 21

• this is from the mid point of the right arm and the left arm - flows to the positive left leg electrode - displays as net positive on the ECG insert pic

Question 22

*what is eithovens triangle?

Answer 22

an imaginary formation formed by the 3 limb leads - the heart is at the centre and represents zero potential when the voltages are summed up - insert pic

Question 23

what do the boxes stand for in ECG graphs?

Answer 23

• on an ECG 10 small squares up = 1mv - 10 small squares across = 400 ms - 1 small square box = 0.1mV for 40ms

Question 24

how many leads are there?

Answer 24

there are 12 leads

Question 25

what are the chest pre cordial leads?

Answer 25

• there are 6 leads and 6 recordings
• the chest leads measure the depolarisation currents in the horizontal plane of the heart

(compared to the limb leads which measure the depolarisation current in the frontal plane of the heart)

• there are 6 unipolar leads V1-V6

for each lead the chest lead is the positive pole

• the negative pole is wilsons central terminal