Cardiac Output

Question 1

What is bradycardia and what would its ECG look like?

Answer 1

Impulses originate at SAN at slower rate

A sinus rhythm of less than 60/min

May be a consequence of increased vagal or parasympathetic tone

ECG: All complexes normal, evenly spaced out BUT rate of <60/min

Question 2

What is Sinus Tachycardia and what would its ECG look like?

Answer 2

Impulses orginate at SAN at a rapid rate.

All complexes normal, evenly spaced. Rate >100/min

Higher than 100/min is classed as sinus tachycardia

It occurs most often as a physiological response to:

Physical exercise or physical stress

May also result from congestive heart failure

Question 3

What does first degree heart block cause?

Answer 3

AV block, first degree= Atrioventricular conduction lengthened. Increased delay of the AVN node.

Abnormal slow conduction in the AVN can result in incomplete heart block- causes an extended PR interval

Question 4

What does second degree heart block cause?

(Wenckebach)

Answer 4

Sudden dropped QRS-complex (missing QRS complex). Because the conduction is delayed for a very long time the QRS complex is missed out.

Heart block occurs when a fraction of impulses from atria are conducted

If the PQ-interval is longer than normal and the QRS complex sometimes does not follow the P wave, the atrioventricular block is second degree.

Question 5

What is third degree heart block?

Answer 5

When the atria and ventricles are depolarising indepedently.

This can suddenly lead to cardiac death.

Question 6

What are the two stages in the cardiac cycle?

Answer 6

Diastole:Ventricles are relaxed and not contracting

Systole: Ventricles contract and eject blood into the aorta and pulmonary artery

Question 7

How do you calculate the normal cardiac output using the end diastolic and systolic volumes?

Answer 7

CO= HR x (EDV-ESV) ( end-diastolic volume- End-systolic volume)

In normal 70kg - CO ~ 5L/min

CO= 70 x (120-50)

= 70/min x 70mL

~ 5 L/ min

Question 8

What are the 7 phases in the cardiac cycle?

Answer 8

Phase 1: Atrial contraction

Phase 2: Isovolumetric contraction

Phase 3: Rapid ejection

Phase 4: Reduced ejection

Phase 5: Isovolumetric relaxation

Phase 6: Rapid filling

Phase 7:Reduced filling

Question 9

What rate can your cardiac output increase to whilst excercising

Answer 9

Exercise can increase output to 25L/min

Question 10

If activity in the parasympathetic system increase, how does this effect heart rate?

Answer 10

Heart rate decreases.

Question 11

If activity in the sympathetic system increase, how does this effect heart rate?

Answer 11

Heart rate increases.

Question 12

What are chronotopic agents?

Answer 12

Influences the currents which then alter the slope of the pacemaker and thus the Heart rate.

Question 13

Give 2 examples of chronotropic agents?

Answer 13

Noradrenaline: Increases HR

Acetylcholine: Decreases HR

Question 14

What are inotropic agents?

Answer 14

These alters the force or energy of muscular contractions.

Question 15

Give 2 examples of inotropic agents.

Answer 15

Positive inotropic agent (increase contractility) e.g, digoxin.

Negative inotropic agent (decrease contractility e.g, beta-blockers (propranolol)

Question 16

What is End-diastolic volume?

Answer 16

Filled volume of ventricle prior to contraction(~120ml)

Question 17

What is End-systolic volume?

Answer 17

Volume of blood remaining in the ventricals after ejection(~50ml)

Question 18

How do you calculate SV using EDV and ESV?

Answer 18

SV= EDV-ESV

Question 19

What is preload?

Answer 19

Volume of blood entering ventricles.

Question 20

What is afterload?

Answer 20

Resistance in the ateries as blood leaves th eleft ventricle

Question 21

What 2 factors influence SV?

Answer 21

Increased preload during hypervolemia

Increased afterload during hpertesnion vasoconstriction

Question 22

What is hypervolemia?

Answer 22

When there is too much fluid in the blood due to increase sodium content.

Question 23

What is the Frank Starling Mechanism?

Answer 23

It describes the relationship between EDV and SV.

The effect is due to the heart msucle firbres responding to stretch by contracting more forcefully.

This is not due to elastic effect but due to an increased expenditure of ATP energy.

Question 24

How woudl you go about increasing SV?

Answer 24

Increase EDV.

Question 25

Where would the line shift in a patient when they are excercising?

Answer 25

Shift left and upwards

Question 26

Where would the line shift when a patient has heart failure?

Answer 26

Right and down

Question 27

What cardiac drugs are used to alter cardiac output and to treat hypertension

Answer 27

Question 28

What is the difference between 2nd degree heart block type 1 and 2?

Answer 28

Type 1:Has a wenckebach pattern- prolongonged PQ until QRS goes missing

Type 2: No pattern, QRS is missing throughout

Question 29

Describe atrial contraction?

Answer 29

• It initiates the P wave on the ECG
• Represents the electrical depolarisation of the atria

Question 30

Describe isovolumetric contraction?

Answer 30

• Begins with at the start of the QRS complex
• Represents ventricle depolarisation
• This triggers excitation-contraction coupling, myocyte contraction and a rapid increase in intraventricular pressure.

Question 31

Describe Rapid ejection.

Answer 31

• Ejection begins when the intraventricular pressures exceed the pressures within the aorta and pulmonary artery, which causes the aortic and pulmonic valves to open.

Question 32

Describe rapid ejection

Answer 32

• After the QRS and the beginning of ventricular contraction, ventricular repolarization occurs as shown by the T-wave.

Question 33

Decribe Isovolumetric Relaxation.

Answer 33

• When the intraventricular pressures fall sufficiently at the end of phase 4, the aortic and pulmonic valves abruptly close (aortic precedes pulmonic) causing the second heart sound (S2) and the beginning of isovolumetric relaxation.

Question 34

Describe Rapid filling.

Answer 34

• As the ventricles continue to relax at the end of phase 5, the intraventricular pressures will at some point fall below their respective atrial pressures. When this occurs, the AV valves rapidly open and passive ventricular filling begins. Despite the inflow of blood from the atria, intraventricular pressure continues to briefly fall because the ventricles are still undergoing relaxation.

Question 35

Describe reduced filling.

Answer 35

As the ventricles continue to fill with blood and expand, they become less compliant and the intraventricular pressures rise. The increase in intraventricular pressure reduces the pressure gradient across the AV valves so that the rate of filling falls late in diastole.