Cardiac cycle

Question 1

What is a phonocardiogram?

Answer 1

A chart or record of the sounds made by the heart

Question 2

What events generate the 4 heart sounds that can sometimes be heard in the horse

Answer 2

S1= closure of the AV valves 
S2= closure of the semilunar valves
S3= rapid ventricular filling 
S4= ventricular filling due to atrial contraction

Question 3

What is a Wiggers diagram?

Answer 3

A diagram that describes the pressure and volume relationships which occur during each cardiac cycle

Question 4

What event occurs during the “a” wave of a Wiggers diagram

Answer 4

Pressure increase due to atrial contraction at the end of diastole

Question 5

What event occurs during the “c” wave of a Wiggers diagram

Answer 5

Pressure increase due to the tricuspid valves bulging into the atrium as a result of ventricular contraction

Question 6

What event occurs during the “x” descent of a Wiggers diagram

Answer 6

A drop in atrial pressure during ventricular systole caused by atrial relaxation

Question 7

What event occurs during the “v” wave of a Wiggers diagram

Answer 7

Increase in atrial pressure as the atrium begins to fill during late diastole

Question 8

What event occurs during the “y” descent of a Wiggers diagram

Answer 8

Atrial pressure drop as blood enters the ventricle during diastole

Question 9

What are the 5 phases of a Wiggers diagram

Answer 9

1. Atrial contraction
2. Ventricular isovolumetric contraction
3. Ventricular ejection (ventricular systole )
4. Ventricular isovolumetric relaxation
5. Passive ventricular filling

Question 10

How would you get a catheter into the left ventricle

Answer 10

1. Blood flow opposes the passage of the catheter, therefore a stiff catheter has to be used
2. The left carotid artery is exposed by a midline neck incision to expose the trachea
3. The internal carotid artery can then be pulled out and dissected off of the vagus nerve
4. The catheter is passed down the internal carotid artery, usually going directly into the left ventricle, which is shown by the diastolic pressure dropping to low values
5. Need to be careful as the catheter can be passed down the ascending aorta instead

Question 11

How would you get a catheter into the right ventricle

Answer 11

The right external jugular vein is dissected out and the Swan Ganz catheter is passed down the venous system until the pressures recorded from it match that of the right ventricle
Easier to get in as the blood flow matches the direction of the catheter

Question 12

What would you use a catheter in a ventricle for

Answer 12

Indicator dilution studies (helps estimate blood velocity)
Blood withdrawal for gas analysis
Fluoroscopic radiography (locating the catheter)
Look at the path of blood flow through the heart using dye (angiography)
Recording pressure in different chambers
Repair of structural issues (e.g. closing septal defects, pacemaker implantation)

Question 13

What would the consequences of mitral valve failure be

Answer 13

Blood may leak/ flow backwards into the atrium, reducing the heart’s efficiency
The heart will have to work harder to pump the same volume of blood
Increased left atrial volume and pressure, reduced resistance to left ventricular ejection, reduced forward stroke volume
Eventually congestive heart failure will occur