Lecture 1- Cardiac cycle

Question 1

Describe Aortic pressure during the cardiac cycle

Answer 1

1. Low (80mmHg) when aortic valve open
2. Peaks during ejection and then lowers
3. Aortic valve closes and slowly returns to normal

Question 2

Describe atrial pressure during CC

Answer 2

1. Increases in atrial systole

2. .decreases in ejection

Question 3

Describe ventricular pressure in CC

Answer 3

1. slightly increases in atrial systole
2. Rapid increase ub usivolumetric contraction
3. Peaks at ejection and decreases rapidly when AV valves close

Question 4

Describe ventricular volume in CC

Answer 4

1. Lowest after ejection
2. stays the same in isovolumetric relaxation
3. rapid increase in volume in diastole

Question 5

Describe an ECG trace in the CC

Answer 5

P- atrial contraction
QRS- ventricular contraction
ST- diastole

Question 6

Where does electrical signal originate from?

Answer 6

SAN

Question 7

Which tracts does electrical signals branch into from SAN

Answer 7

1. Anterior - tract of bachman
2. Middle- tract of wenckeback
3. Posterior - tract of Thorel

Question 8

Where do the internodal pathways meet

Answer 8

AVN

Question 9

What conduction pathways does the Bundle of His consist of?

Answer 9

1. RBB

2. LBB –> LAF / LPF

Question 10

what does the Bundle of His link to

Answer 10

Purkinje system

Question 11

Describe the function of the SA node

Answer 11

-specialised neurocardiac tissue
-pacemaker
-Connected directly to surrounding artial muscle fibres
SELF-EXCITATION
RHYTHMICITY

Question 12

Describe the conduction of an electrical impulse in terms of timing

Answer 12

1. SAN –> 3 bands (1m/s) and atria (0.3m/s)
2. 0.09s delay in AVN
3. 4m/s through purkinje fibres –> due to loads of gap junctions
4. 0.4-0.05 m/s transmission in ventricular muscle

Question 13

Why is there a 0.09s delay in the AVN

Answer 13

reduced gap junctions

allows ventricles to fill completely before contraction

Question 14

Describe Phase 0 of an action potential in a ventricular muscle fibre

Answer 14

Rapid depolarization –> opening of fast Na channels

Question 15

Phase 1 ventricular action potential

Answer 15

rapid depolarisation –> closure of Na channels

Question 16

Phase 2 ventricular action potential

Answer 16

plateau –> slow prolonged opening of Ca channels

Question 17

Phase 3 Ventricular action potential

Answer 17

final repolarization –> Ca channels close

Question 18

Phase 4

Answer 18

RMP –> -85-90 opening of K channels

Question 19

Effect of parasympathetic stimulation (microscopic)

Answer 19

releases Ach

1. Reduces rhythm of SAN–>RMP becomes more negative
2. reduces excitability of A-V junctional fibres

Question 20

Effect of parasympathetic stimulation (macroscopic)

Answer 20

slowing of HR
if a strong vagal stimulus occurs the ventricles can stop beating for 5-20s the purkinje fibres take over and ventricles contract at 15-40bpm

Question 21

Effect of sympathetic stimulation (microscopic)

Answer 21

Noradrenaline released

1. Increase rate of SAN discharge –> RMP more positive
2. increased rate of conduction and overall excitability
3. increase force of contraction –> Ca2+permeability increased

Question 22

Effect of sympathetic stimulation (macroscopic)

Answer 22

Increased HR

Increased strength of contraction

Question 23

What is excitation-contraction coupling

Answer 23

Mechanism by which AP causes myofibrils to contract

Question 24

What happens in the first two stages of excitation-contraction ?

Answer 24

1. AP reaches T-tubule and depolarises muscle cell membrane

2. Calcium enters muscle cells through DHP receptors in phase 2

Question 25

What happens during the last two stages of excitation-contraction?

Answer 25

3. Presence of calcium causes the release of more calcium goes from 10-7 to 10-5M 4. Ca ions catalyse sliding of actin-myosin filaments

Question 26

What occurs in atrial systole

Answer 26

- Atrial depolarisation - atrial contraction - atrial pressure rise - blood flows across AV valves

Question 27

What are the features of atrial systole

Answer 27

JVP- a wave ECG - P wave precedes and PR is depolarisation S4 can be heard here

Question 28

What occurs in isovolumetric contraction

Answer 28

- Ventricular rises above atrial pressure which causes AV valves closed - after 0.02s semilunar valves open - period between AV close and semilunar opening contraction occurs without emptying

Question 29

What are the features of isovolumetric contraction

Answer 29

JVP - c wave ECG - interval between R-S Heart sounds S1 closure of AV valves

Question 30

What occurs in ejection

Answer 30

- LV pressure rises above 80 / RV pressure above 8 - semilunar valves open - rapid ejection --> 70% emptied in first 1/3 - slow ejection --> 30% in last 2/3

Question 31

What are the features of ejection

Answer 31

JVP- no waves ECG - T wave No heart sounds Aortic pressure--> rapid rise in pressure and slightly maintained due to elastic recoil

Question 32

What occurs in isovolumetric relaxation

Answer 32

Arterial pressure is greater than ventricular Semilunar valves close to prevent backflow 0.03-0.06 ventricular relaxation despite no change in volume -atria fill and pressure increases -this stage finishes when atrial pressure is greater than ventricular

Question 33

Features of isovolumetric relaxation

Answer 33

JVP - v wave ECG - no deflections Sounds - S2 semilunar valve closure Aortic pressure curve- incisura--> short period of backflow before valves closes

Question 34

what occurs in ventricular filling

Answer 34

``` AV valves open 1. rapid filling first 1/3 2. reduced filling middle 1/3 3.final 1/3 enters heart through atrial contraction as atrial pressure falls ```

Question 35

Features of ventricular filling

Answer 35

JVP- y descent ECG- no deflections S3 pathological sound

Question 36

What is the force-velocity relationship

Answer 36

increase in afterload=decrease in shortening velocity

Question 37

Volume/pressure changes in systolic dysfunction

Answer 37

Impaired ventricular function EDV increases inability to contract and pump blood out of ventricles

Question 38

Volume/pressure changes in diastolic dysfunction

Answer 38

Impaired relaxation ability reduced EDV inability for ventricles to relax

Question 39

What occurs in mitral stenosis

Answer 39

Impaired LV filling reduced EDV reduced afterload and ESV reduced SV + CO

Question 40

what occurs in mitral regurg

Answer 40

outflow resistance decreases EDV + EDP increases stroke volume increases EF decreases

Question 41

what occurs in aortic stenosis

Answer 41

``` high outflow resistance LV emptying impaired peak systolic pressure increases afterload increases SV decreases ESV increases EDV increases ```

Question 42

what occurs in aortic regurg

Answer 42

isovolumetric relaxation cannot occur blood moves from aorta to ventricle throughout diastole EDV increases SV increases