Week 3 - Heart Axis & Cardiac Flow

Question 1

What is a rhythm strip?

Answer 1

the voltage shift as waves of electrical activity sweep over the heart

Question 2

What is the purpose of a ground electrode?

Answer 2

• forms a baseline
• valued 0 in the ECG

Question 3

What is the range for a normal cardiac axis?

Answer 3

-30º to +110º

Question 4

What are the three auxiliary leads?

Answer 4

• aVR, aV, aVF
• used by clinics
• leads in the 3^rd dimension

Question 5

What is asystole?

Answer 5

• flatline
• beware of faulty equipment and connections

Question 6

What are all the changes in pressure in the left side of the heart and the reason for the changes?

Answer 6

atrial pressure
- blood slowly filling causes a rise in pressure
- decrease at isovolumic contraction
- mitral valve closes
- ventricle contraction bends the atrium causing a rise in pressure
- constant filling causes pressure to slowly rise
- mitral valve opens

ventricular pressure
- blood slowly filling causes a rise in pressure
- decrease at isovolumic contraction but higher than atrial pressure
- mitral valve closes
- contraction causes a rapid increase in pressure
- aortic valve opens
- blood is ejected causing a slight decrease in pressure
- aortic valve closes slightly after isovolumic relaxation due to blood pressure making the overall pressure of ventricles still higher than aortic pressure at intersection point
- rapid inflow of blood causes a rapid decrease in pressure
- mitral valve opens

aortic pressure
- generally higher pressure due to constant contraction to keep the blood flowing
- aortic valve opens
- blood flowing in causes an increase in pressure
- blood flows through causes a decrease in pressure
- aortic valve closes a little later
- blood meets area of resistance causing a reflected wave of pressure to hit in the aorta, causing a slight increase

Question 7

What is SV?

Answer 7

Stroke Volume
- represented in the graph by the horizontal length inside the loop

Question 8

What does the area inside the loop represent?

Answer 8

amount work that the heart is doing

Question 9

What is preload?

Answer 9

volume of blood in the chamber at the end of diastole

Question 10

What factors cause an increase of preload?

Answer 10

increased atrial contractility
- more blood is pushed into the ventricles
decreased heart rate
- more time for blood to flow in as it constantly keeps filling
increased central venous pressure
- venous end is where most blood is waiting
- that blood is pushed into the heart

Question 11

What is the effect of preload on a pressure-volume loop?

Answer 11

• increase in venous return
• EDV increase
• SV increase
• EDVPR curve still followed
• loop stretches towards the right

Question 12

What is afterload?

Answer 12

pressure the heart has to pump against to push the blood forward

Question 13

What is the effect of a higher afterload?

Answer 13

• there is an increase aortic pressure
• lower ventricular emptying
• pressure to move blood forward and cannot eject more blood from ventricles

Question 14

What is the effect of a higher afterload on the pressure-volume loop?

Answer 14

• increased pressure
• increased ESV
• decreased SV
• loop stretches upwards

Question 15

What is the effect of an increased ventricular compliance?

Answer 15

• inverse of stiffness
• increased preload
• EDPVR line shifts upwards
• more pressure can be applied to heart muscle

Question 16

What is the effect of an increased inotropy?

Answer 16

• heart squeezes faster
• lower ESV
• shifts ESPVR line to the left and up