Lecture 20: Excitation-Contraction Coupling of the Heart and Cardiac Cycle

Question 1

Two parts of the cardiac cycle

Answer 1

systole and diastole

Question 2

Systole

Answer 2

Contraction and emptying

Question 3

Diastole

Answer 3

Relaxation and filling

Question 4

Contraction occurs as a result of

Answer 4

excitation across the heart

Question 5

Relaxation follows

Answer 5

the subsequent repolarization of the cardiac muscle

Question 6

Cardiac cycle is divided into how many stages

Answer 6

7

Question 7

Phase A of cardiac cycle

Answer 7

• Atrial contract
• Final phase of ventricular filling
• Increased atrial pressure is reflected back to veins causing venous pressure “a” wave

Question 8

What is associated with the fourth heart sound

Answer 8

Phase A: Atrial systole

Question 9

Fourth heart sound

Answer 9

• Not heard under normal conditions
• May be heard when ventricle compliance is decreased and forceful ventricular filling produces a sound
• Ex. Ventricle hypertrophy

Question 10

Phase B: Isovolumertric Ventricular Contraction

Answer 10

• Ventricles contract and ventricular pressure increases
• All valves are closed, and closure of AV valves produces the first heart sound (S1)
• C wave occurs here

Question 11

S1 signals the onset of

Answer 11

Ventricular systole

Question 12

“C” wave

Answer 12

Increase of ventricular pressure leads to bulging of AV valve into atria, causing a small atrial pressure wave
Occurs during phase B

Question 13

Two atrioventricular valves

Answer 13

Tricuspid valve

Mitral valve

Question 14

First heart sound

Answer 14

Two nearly superimposed components:
-Mitral component slightly precedes triscupid component because the earlier electrical stimulation of left ventricular contraction

Question 15

Phase C: Rapid Ventricular Ejection

Answer 15

• Ventricles contract
• Ventricular pressure increases and reaches the maximum
• Aortic valve opens
• Ventricles eject blood into arteries
• Ventricular volume decreases
• Aortic pressure increases and reaches maximum

Question 16

Two semilunar valves

Answer 16

1. Pulmonary valve

2. Aortic valve

Question 17

Afterload

Answer 17

The pressure against which the heart pumps blood into the circulation

Question 18

Phase D: Reduced Ventricular Ejection

Answer 18

• Ventricles eject blood into the aorta at a slower rate
• Ventricles do not empty completely
• Aortic pressure begins to fall

Question 19

End-systolic volume

Answer 19

The amount of blood remaining in the ventricle at the end of systole

Question 20

Stroke volume

Answer 20

The amount of blood ejected by the ventricle in one beat

Question 21

The proportion of EDV that is ejected

Answer 21

(SV/ESV) = Ejection fraction

Question 22

Phase E: Isovolumetric Ventricular Relaxation

Answer 22

• Ventricles relaxed
• Ventricular pressure decreases
• Aortic valve closes
• Second heart sound is heard
• Ventricular pressure is constant (end-systolic volume)
• V wave

Question 23

V wave

Answer 23

Atrial pressure increases as a result of filling from the veins

Question 24

Dicrotic notch

Answer 24

Closure of the aortic valve produces a disturbance on the aortic pressure curve

Question 25

Second heart sound

Answer 25

- Aortic valve closes slightly before the pulmonary valve, leading to this sound - Inspiration delays the closure of the pulmonic valve, which causes the splitting of the S2

Question 26

Why does splitting of S2 occur during inspiration?

Answer 26

- Associated decrease of intrathoracic pressure produces an increase in venous return to the right side of the heart - Resulting increase in right ventricular EDV causes an increase in right ventricular SV and prolongs right ventricular ejection time - Prolongation of ejection time delays the closure of the pulmonic valve relative to the aortic valve

Question 27

Phase F: Rapid Ventricular Filling

Answer 27

- Ventricles relaxed - Mitral valve opens - Ventricles fill passively with blood from the atria - Ventricular volume increases - Ventricular pressure low - Rapid ventricular filling may produce as a third heart sound

Question 28

Third heart sound

Answer 28

Occurs early in diastole following the opening of the AV valves

Question 29

Phase G: Rapid Ventricular Filling

Answer 29

- Ventricles relaxed | - Final phase of ventricular filling

Question 30

Ventricular pressure-volume loop

Answer 30

Ventricular pressure plotted against volume

Question 31

Heart murmurs

Answer 31

Sounds generated by turbulent flow in the surrounding

Question 32

Five things heart murmurs may result from

Answer 32

1. Flow across a partial obstruction (ex. aortic stenosis) 2. Regurgitant flows across an incompetent valve (ex. mitral reguritation) 3. Increase flow through normal structures (ex. Systolic murmurs associated with a high output state, during anemia) 4. Ejection into dilated chamber (ex. dilated aorta) 5. Abnormal shunting of blood from one vascular chamber to a lower pressure chamber (ex. ventricular septal defect)

Question 33

Heart murmurs may be described by their (5)

Answer 33

1. Timing 2. Intensity 3. Pitch 4. Shape 5. Location

Question 34

Timing

Answer 34

Whether it occurs during systole, diastole, or is continuous (begins in systole and continues into diastole)

Question 35

Intensity

Answer 35

- Ease in which it is identified/heard | - Murmurs are typically quantified by a grading system

Question 36

Systolic murmur intensity grading

Answer 36

1/6 to 6/6 with 1 being barely audible and 6 being audible without stethoscope directly on chest wall

Question 37

Diastolic murmur intensity grading

Answer 37

1/4 to 4/4 with 1 being barely audible and 4 being very loud

Question 38

Pitch

Answer 38

- Frequency of the murmur ranging from high to low - High frequency murmurs are caused by large pressure gradients between chambers (ex. aortic stenosis) - Low frequency murmurs implies less of a pressure gradient between chambers (mitral stenosus)

Question 39

Shape

Answer 39

How the murmur changes in intensity from onset to completion

Question 40

Three examples of murmur shape

Answer 40

1. Crescendo-decrescendo - first rises then fall off in intensity 2. Decrescendo - murmur begins at maximum intensity, then falls 3. Continuous - heard throughout the cardiac cycle

Question 41

Location

Answer 41

- Region of maximal intensity - Murmurs are often heard to radiate from their primary location to other areas of the chest. Such patterns of transmission relate to the direction of the turbulent flow

Question 42

Three defects that cause heart murmurs

Answer 42

1. Ventricular septal defect 2. Changes in blood pressure in a particular region of the body 3. Cardiac hypertrophy

Question 43

Ventricular septal defect (murmur consequences)

Answer 43

- Initially, the increased blood return to the left ventricle augments stroke volume (via the Frank-Starling Mechanism) - Over time the increased volume load can result in chamber dilation and heart failure

Question 44

Changes in blood pressure in a particular region of the body - mitral stenosis example (murmur consequences)

Answer 44

- Blood dams up in the left atrium which means the left atrial pressure in higher than normal - High left atrial pressure is passively transmitted to the pulmonary circulation which leads to... - Increased pulmonary venous and capillary pressures leads to.... - The transduction of plasma into the lung interstitium which leads to... - Congestive heart failure

Question 45

Cardiac hypertrophy (murmur consequences)

Answer 45

Increase in workload of one or both ventricles