Cardiovascular - The Cardiac Cycle

Question 1

Classify the phases of the cardiac cycle

Indicate the classical ‘start’ point of the cardiac cycle (i.e. the start of the Wigger’s diagram.

Answer 1

Diastolic

1. Isovolumetric relaxation
2. Early/rapid ventricular filling
3. Late/slow ventricular filling - START
4. Atrial Contraction

Systolic

1. Isovolumetric contraction
2. Ejection

Question 2

What percentage of ventricular filling is accomplished by the atrial ‘kick’ or atrial contraction. How is this different in exercise and why?

Answer 2

10%

Exercise: atrial ‘kick’ increased to 40% as diastolic time is much shorter

Question 3

What causes the first heart sound

Answer 3

When ventricular pressure exceeds atrial pressure, the AV valves close –> S1

Question 4

Which AV valve closes earlier

Answer 4

The mitral valve –> slightly split S1

Question 5

What causes the a, c and v waves and the x and y descents on the central venous pressure waveform?

Answer 5

a wave - atrial contraction
c wave - tricuspid valve bulges into right atrium during isovolumetric contraction
v wave - Venous return from lungs and vena cava (throughout late systole)

x descent - RV contraction during ejection –> downward pull on the tricuspid valve –> rapid decline in RAP.
y descent - Opening of the AV valve with rapid flow into ventricles and fast reduction in atrial pressure

Question 6

What causes the second heart sound S2?

Answer 6

As the ventricular pressure falls (ventricular myocytes start to depolarise) –> ventricular pressure falls below aortic (and pulmonary) pressure –> closure of the semilunar valves –> S2

Question 7

What is physiological splitting of the second heart sound?

Answer 7

Aortic valve closes before pulmonary valve. This effect is accentuated during inspiration. (Negative intrathoracic pressure during inspiration reduces pulmonary pressures even further which means that it takes longer for RV pressure to fall below pulmonary artery pressure

Question 8

What is the dichrotic notch

Answer 8

It is a positive deflection in the aortic pressure curve subsequent to closure of the aortic valve and caused by elastic recoil of the aortic valve and aorta

Question 9

What is the mechanism of the third heart sound S3

Answer 9

Increased volume of atrial blood (e.g. mitral regurgitation or LVF) flowing into a poorly compliant LV results in reverberation of the ventricular wall during early diastole and the third heart sound results S3

Question 10

What is stroke volume?

Answer 10

Volume of blood ejected from the heart per heart beat

Question 11

What is the formula for SV

Answer 11

SV = LVEDV - LVESV

Question 12

What is normal LVEDV, LVESV and SV

Answer 12

LVEDV = 120
LVESV = 50
SV = 70 ml

Question 13

What is the formula and normal range for ejection fraction

Answer 13

EF = LVEDV - LVESV
____________
LVEDV

EF = SV/LVEDV

EF = 70/120

EF = 58%

Normal range is 55 - 70%

Question 14

What is the optimal heart rate range for optimal cardiac output and why?

Answer 14

CO = HR x SV
Logical that increased HR –> increased CO

BUT
cardiac cycle is 0.8 seconds
Normally: Systole 0.3 seconds and diastole 0.5 seconds

Heart rate of 200 beats per minute during exercise
–> cardiac cycle 0.3 seconds
–> systolic time: 0.15 seconds
–> diastolic time: 0.15 seconds
SUCH a short diastolic time limits ventricular filling

optimal HR 50 –> 150 beats per minute

Question 15

List the changes that the heart undergoes with age

Answer 15

1. Reduced aortic compliance –> increased afterload –> LV hypertrophy –> reduced LV compliance.
2. Fibrosis of atrial pacemakers –> predisposes to atrial fibrillation

Question 16

what is the formula for HRmax

Answer 16

208 - (0.7 x age)
HRmax at 20 = 194
HRmax at 80 = 152

Question 17

How does importance of atrial contraction change with age?

Answer 17

Contributes up to 40% of LVEDV due to reduced LV compliance

Question 18

Define systole and diastole

Answer 18

SYSTOLE is the period of chamber contraction and blood ejection which corresponds to:

• period between onset QRS and end of T wave ECG
• period between AV closure and semilunar valve closure

DIASTOLE is the period of chamber relaxation and cardiac filling which corresponds to

• period between the end of the T wave and the end of the PR interval
• The period during which the Mitral and Tricuspid valves are open

Question 19

Why does flow occur out of the LV into the aorta

Answer 19

Small pressure difference between LV and aorta –> required for flow to occur

Question 20

What is a normal LV- aorta pressure gradient

What is the pressure gradient in mild, moderate and severe aortic stenosis (include valve areas)

Answer 20

Normal 5 mmHg

Mild AS –> 5 -25 mmHg (Area > 1.5cm^2)
Moderate –> 25 - 40 mmHg (Area 1 - 1.5 cm^2)
Severe –> > 40 mmHg (Area 0.5 - 1 cm^2)
Critical –> > 80 mmHg (Area < 0.5 cm^2)