L8 - electrical & mechanical events of cardiac cycle

Question 1

what is the order an impulse travels through the heart

Answer 1

SA node 
through atrial wall to 
AV node (pause)
bundle of His 
purkinje fibres 
apex

Question 2

what does slower diastolic depolarisation of the SA node lead to

Answer 2

slower HR

Question 3

what determines the rate of depolarisation of the SA node

Answer 3

funny current (pacemaker current ) If

carried through HCN channels

Question 4

increased size of funny current =

Answer 4

faster depolarisation - faster HR

Question 5

what is the purpose of the pause at the AV node

Answer 5

allows ventricle filling

prevents transmission of many impulses (Atrial fibrillation)

Question 6

what is P wave

Answer 6

atrial depolarisation

Question 7

what is QRS wave

Answer 7

ventricular systole

Question 8

what is Q point

Answer 8

depolarisation of septum towards atria

Question 9

what is R point

Answer 9

depolarisation of ventricles towards apex

Question 10

what is S point

Answer 10

depolarisation of ventricles towards atria

Question 11

what is T wave

Answer 11

ventricular repolarisation

Question 12

why cant atrial repolarisation be seen?

Answer 12

obscured by ventricular systole

Question 13

what does the P-S interval represent

Answer 13

atrial AP

Question 14

what does the Q-T interval represent

Answer 14

ventricular AP

Question 15

how are intervals measured eg Q-T

Answer 15

from the start of Q to the start of T (not including T)

Question 16

what is the P-Q interval duration a measure of

Answer 16

atrial conduction + AV node delay

Question 17

what is QRS duration a measure of

Answer 17

speed of ventricular conduction from top to bottom

Question 18

what is S-T interval

Answer 18

segment where entire ventricle is depolarised

Question 19

what can a change in a patients S-T segment show?

Answer 19

part of the ventricles are not depolarising as they should - could be a sign of myocardial infarction

Question 20

what is isovolumetric contraction

Answer 20

when ventricle is full of blood and contracts but SL valves aren’t yet open so pressure increases but volume stays the same

Question 21

when do SL valves open?

Answer 21

when the pressure inside ventricle is higher than either aorta or pulmonary artery

Question 22

what is the dichroitic notch

Answer 22

the point at which ventricle is emptying and its pressure falls below the aortic pressure so aortic AL valve shuts

Question 23

what is isovolumetric relaxation

Answer 23

the period after SL valve has shut so volume inside ventricle stays the same but the ventricle is relaxing so pressure decreases

Question 24

how is stroke vol calculated from pressure volume loop

Answer 24

width of loop

distance from the left line (lowest vol) to right line (highest vol)

Question 25

how is stroke work measured from pressure volume loop

Answer 25

area of loop

if heart working harder - bigger area

Question 26

what is ejection fraction

Answer 26

fraction of blood in heart at the end of diastole (when ventricle is full), that is ejected with each beat

Question 27

what is ejection fraction formula

Answer 27

SV/ EDV x 100

Question 28

what nerves innervate SA node

Answer 28

SNS - accelerator nerve

PSNS - vagus

Question 29

is conduction quicker through atria or ventricles

Answer 29

ventricles