2: Cardiac Conduction

Question 1

What is cardiac conduction?

Answer 1

Depolarization, NOT contraction

Question 2

What are the four steps of cardiac conduction?

Answer 2

1. SA node
2. AV node
3. Bundle of his
4. Purkinjie system

Question 3

How does electrical information spread to the left atria?

Answer 3

Bachman’s bundle that transfers info during cross from SA to AV node

Question 4

What is the cardiac cycle?

Answer 4

Includes all events that occur during the filling phase, the pressure development phase, and the ejection phase

Question 5

What is the filling phase called?

Answer 5

Diastole

Question 6

What is the ejection phase called?

Answer 6

Systole

Question 7

What are the four phases of the cardiac cycle?

Answer 7

1. Passive ventricular filling
2. Atrial ejection
3. Isovolumic contraction phase
4. Ejection phase, rapid then slow

Question 8

What three things are happening during the passive ventricular filling phase of the cardiac cycle?

Answer 8

1. AV valves are open and blood flows from atria to ventricles
2. Blood flows through coronary arteries while the heart is relaxed so there is space to move
3. SA fires leading to atrial contraction

Question 9

What two things are happening during atrial ejection?

Answer 9

1. Atria contracts
2. Conduction to AV and bundles

Question 10

How long is the delay in conduction from SA to AV node and why?

Answer 10

0.1 milliseconds in order to allow for atrias to fully contract

Question 11

What two things are happening during the isovolumic phase?

Answer 11

1. AV valves close (S1), increased ventricular wall pressure
2. Conduction completes through both ventricles, ventricular depolarization

Question 12

What two things are happening during the ejection phase?

Answer 12

1. Aortic and pulmonary valves open
2. Ventricles eject blood

Question 13

What four things happens following the ejection phase?

Answer 13

1.Ventricles relax
2. Aortic and pulmonary valves close (S2)
3. End of T wave
4. Enter diastole and AV valves open again

Question 14

What is preload?

Answer 14

The amount of tension in muscle fibers of the entire chamber before it contracts. Endiastolic pressure

Question 15

What five things affect preload?

Answer 15

1. Active atrial contraction
2. HR in terms of diastolic filling time
3. Venous return (VR)
4. Total blood volume
5. Ventricular compliance, ease of distension during chamber filling

Question 16

What is afterload?

Answer 16

Load against which the muscle exerts its contraction. Ensystolic pressure

Question 17

What five things affect afterload?

Answer 17

1. Peripheral resistance
2. Stroke volume
3. End-diastolic volume
4. Impedance (blood viscosity and aortic compliance)
5. Presence of outflow obstruction

Question 18

What is left ventricular ejection fraction?

Answer 18

Definitive measure of cardiac function

Question 19

What is ejection fraction and the normal value?

Answer 19

All that is needed for a normal HR, 55-60%

Question 20

What happens to ejection fraction in times of high stress?

Answer 20

Can increase to as much as 90-95% of its total volume capacity as stroke volume