The Cardiac Cycle

Question 1

Regarding the anatomy of the heart (true or false):

The heart is a specialised hollow muscular pump measuring 9 cm long by 9 cm wide and weighs
250-350 g

Answer 1

False. The heart is a specialised hollow muscular pump, however, it measures 12 cm long by 9 cm wide and weighs 250-350 g.

Question 2

Regarding the anatomy of the heart (true or false):

The heart has four chambers built on a ring of fibrous tissue at the atrioventricular junction

Answer 2

True. The heart has four chambers built on the annulus fibrosus, which is a ring of fibrous tissue at the atrioventricular junction

Question 3

Regarding the anatomy of the heart (true or false):

Valves within the heart ensure the unidirectional flow of blood

Answer 3

True. Valves within the heart ensure the unidirectional flow of blood.

Question 4

Regarding the anatomy of the heart (true or false):

The heart is conical in shape

Answer 4

True. The heart is conical in shape and it lies obliquely across the middle of the mediastinum.

Question 5

Regarding the anatomy of the heart (true or false):

The cardiac apex represents the left ventricle and lies behind the third left intercostal space

Answer 5

False. The tip of the cone, or the ‘cardiac apex’, represents the left ventricle and lies behind the fifth left intercostal space.

Question 6

Regarding the anatomy of the heart (true or false):

The anterior surface of the heart is made up of the right atrium and right ventricle

Answer 6

True. Due to the rotation of the heart, its anterior surface is made up of the right atrium and right ventricle.

Question 7

Regarding the anatomy of the heart (true or false):

The base of the heart is posterior facing and is formed mainly by the left atrium

Answer 7

True. The base is posterior facing and formed mainly by the left atrium.

Question 8

Regarding ECGs (true or false):

Electrical activity in heart tissue is simultaneous with the corresponding mechanical event in the cardiac cycle

Answer 8

False. Electrical activity precedes the corresponding mechanical event in the cardiac cycle.

Question 9

Regarding ECGs (true or false):

In a single muscle fibre, contraction starts just after the depolarisation and lasts for 50 ms after repolarisation is completed

Answer 9

True. In a single muscle fibre, contraction starts just after the depolarisation and lasts for 50 ms after repolarisation is completed.

Question 10

Regarding ECGs (true or false):

The P wave is associated with atrial depolarisation and contraction (systole)

Answer 10

True. The P wave is associated with atrial depolarisation and contraction (systole).

Question 11

Regarding ECGs (true or false):

The normal PR interval is 0.16 s

Answer 11

True. The normal PR interval is 0.16 s. The PR interval, between the P wave and the QRS complex, represents the time between the onset of atrial contraction and the beginning of ventricular contraction.

Question 12

Regarding ECGs (true or false):

The QRS complex is <0.12 s in a normal ECG

Answer 12

True. Normally the duration of the QRS complex is <0.12 s: it represents ventricular depolarisation and precedes ventricular contraction.

Question 13

Regarding ECGs (true or false):

The ST segment and T wave are associated with ventricular repolarisation

Answer 13

True. The ST segment and T wave are associated with ventricular repolarisation.

Question 14

Regarding ECGs (true or false):

Ventricular contraction ends during the T wave

Answer 14

False. Ventricular contraction ends after the T wave.

Question 15

Regarding ECGs (true or false):

The U wave is thought to represent the slow repolarisation of the papillary muscles

Answer 15

True. The U wave is thought to perhaps represent the slow repolarisation of the papillary muscles.

Question 16

At a heart rate of 60 bpm, diastole lasts for 0.66 s and systole for 0.34 s. At double the heart rate (true or false):

Diastole lasts for 0.33 s and systole for 0.17 s

Answer 16

False. As heart rate increases, diastole shortens relatively more than systole.

Question 17

At a heart rate of 60 bpm, diastole lasts for 0.66 s and systole for 0.34 s. At double the heart rate (true or false):

Duration of diastole increases

Answer 17

False. The duration of diastole reduces with an increase in heart rate.

Question 18

At a heart rate of 60 bpm, diastole lasts for 0.66 s and systole for 0.34 s. At double the heart rate (true or false):

In a healthy young person, most of ventricular filling occurs during early diastole

Answer 18

True. For a healthy person, at a heart rate of 120 bpm, most ventricular filling occurs during early diastole.

Question 19

At a heart rate of 60 bpm, diastole lasts for 0.66 s and systole for 0.34 s. At double the heart rate (true or false):

There is a linear relationship between heart rate and duration of the cardiac cycle

Answer 19

False. As heart rate increases with strenuous exercise, the phases of the cardiac cycle shorten. However, diastole and systole do not shorten to an equal degree, as shown in the following figure.

Question 20

The four phases of systole occur in the following order:

A. Isovolumetric contraction, atrial systole, rapid ejection, reduced ejection
B. Atrial systole, isovolumetric contraction, reduced ejection, rapid ejection
C. Atrial systole, isovolumetric contraction, rapid ejection, reduced ejection
D. Atrial systole, rapid ejection, isovolumetric contraction, reduced ejection

Answer 20

C.

Question 21

Regarding the 1st and 2nd heart sounds (true or false):

The mitral valve closes before the tricuspid valve

Answer 21

True

Question 22

Regarding the 1st and 2nd heart sounds (true or false):

The pulmonary valve closes before the aortic valve

Answer 22

False

Question 23

The area of the pressure-volume loop of the left ventricle represents which of the following?

A. Ventricular stroke volume
B. Ventricular stroke intensity
C. Ventricular stroke work
D. Compliance, measured as pressure/volume

Answer 23

C. Pressure x Volume can be reduced to Nm = J.

A. Incorrect. Volume is the width of the loop.

B. Incorrect

D. Incorrect. Compliance is the change in volume per change in pressure, i.e. volume/pressure.

Question 24

Regarding right ventricular systole (true or false):

Ejection occurs early in systole due to high pulmonary vascular resistance

Answer 24

False. Ejection occurs early in systole due to low pulmonary vascular resistance.

Question 25

Regarding right ventricular systole (true or false):

The pressure-volume loop of the right ventricle is triangular

Answer 25

True. The pressure-volume loop of the right ventricle is triangular, however, this makes it more difficult to define the individual phases of systole.