Cardio Electrophysiology - Part of Ballam

Question 1

P wave

Answer 1

atrial depolarization

o Does not include atrial repolarization – hidden in QRS complex

Question 2

PR Interval

Answer 2

initial depolarization of the ventricle
o Depends on conduction velocity through AV node
• In heart block – PR interval increases
• Sympathetic nervous system stimulation (B1) increases conduction velocity – PR interval decreases
• Parasympathetic (M) decreases conduction velocity – PR interval increases

Question 3

QRS complex

Answer 3

depolarization of the ventricles

Question 4

QT interval

Answer 4

entire period of depolarization and repolarization of the ventricles

Question 5

ST segment

Answer 5

isoelectric, period when ventricles are depolarized

Question 6

T wave

Answer 6

ventricular repolarization

Question 7

A wave

Answer 7

Venous phase

increase in atrial pressure (venous pressure) caused by atrial systole

Question 8

C wave

Answer 8

Venous phase

bulging of the tricuspid valve into right atrium during right ventricular contraction

Question 9

V wave

Answer 9

Venous phase

blood flow into right atrium – rising phase of the wave; from right atrium into right ventricle – falling phase of wave

Question 10

Phases in Ventricle, atrium and purkinje system cardiac APs and explanation of each

Answer 10

o Phase 0
• Upstroke of AP
• Transient increase in Na+ conductance, inward Na+ current depolarizes membrane

o Phase 1
• Brief period of initial repolarization
• Outward current, movement of K+ ions out of cell, decrease in Na+ conductance

o Phase 2
• Plateau of AP
• Transient increase in Ca2+ conductance – inward Ca2+ current, increase in K+ conductance
• Outward and inward currents equal – membrane potential stable at plateau level

o Phase 3
• Repolarization
• Ca2+ conductance decreases, K+ conductance increases and predominates
• Large outward K+ current hyperpolarizes membrane back to K+ equilibrium potential

o Phase 4
• Resting membrane potential
• Inward and outward currents of K+ equal

Question 11

SA node cardiac AP phases with explanations

Answer 11

o Unstable resting potential

o Phase 0
• Upstroke of AP
• Increase in Ca2+ conductance – increase causes inward Ca2+ current drives membrane toward Ca2+ equilibrium potential.

o Phase 3
• Repolarization
• Increased K+ conductance – outward K+ current repolarizes membrane potential

o Phase 4
• Slow depolarization – pacemaker activity of SA node automaticity
• Increase in Na+ conductance – inward Na+ current – turned on by repolarization

o Phases 1 and 2 not present

Question 12

AV node upstroke of AP

Answer 12

result of inward Ca2+ current

Question 13

Absolute refractory period

Answer 13

begins with upstroke of the AP, ends after the plateau

Question 14

Preload

Answer 14

end-diastolic volume – related to right atrial pressure

o Increased venous return increases end-diastolic volume, stretches or lengthens ventricular muscle fibers

Question 15

Afterload

Answer 15

o aortic pressure – Increases in aortic pressure increases afterload on the left ventricle
o pulmonary artery pressure – increases in pulmonary artery pressure causes increase in afterload on the right ventricle

Question 16

Frank-Starling Relationship

Answer 16

o Increases in stroke volume and cardiac output occur in response to an increase in venous return or end-diastolic volume

o Increases in end-diastolic volume cause an increase in ventricular fiber length, which produces an increase in developed tension

o Mechanism that matches cardiac output to venous return – greater venous return = greater cardiac output

o Changes in contractility shifts Frank-Starling curve upward (increases contractility) or downward (decreased contractility)
• Increased contractility cause increase in CO for any level of right atrial pressure or end-diastolic volume
• Decreased contractility cause decrease in CO for any level of right atrial pressure or end-diastolic volume

Question 17

Ventricular pressure volume loop

Answer 17

• 1 → 2 Isovolumetric contraction
o normal volume about 140 mL – end-diastolic volume
o All valves are closed, no blood ejected from ventricle

• 2 → 3 ventricular ejection
o Aortic valve opens at 2, blood ejected into aorta (stroke volume), ventricular volume decreases
o Volume remaining at point 3 is end-systolic volume

• 3 → 4 isovolumetric relaxation
o ventricle relaxes at point 3, aortic valve closes
o all valves closed, ventricular volume is constant

• 4 → 1 Ventricular filling
o mitral valve opens, filling of ventricle begins
o Ventricular volume increases to about 140 mL – end diastolic volume

Question 18

Increased preload in ventricular pressure-volume loop

Answer 18

o Increased end-diastolic volume due to increased venous return
o Increase in stroke volume – increased width of the pressure-volume loops

Question 19

Increased afterload in ventricular pressure-volume loop

Answer 19

o Increased aortic pressure – ventricle must eject blood against a higher pressure → decrease in stroke volume
o Decreased stroke volume reflected in decreased width of the pressure-volume loop.
o Decrease in stroke volume results in an increase in end-systolic volume

Question 20

Increased contractility in ventricular pressure-volume loop

Answer 20

o Ventricle develops greater tension, causing increase in stroke volume
o Decrease in end-systolic volume

Question 21

Cardiac and vascular function curves

Answer 21

• Cardiac output as a function of end-diastolic volume
• Venous function – relationship between blood flow and right atrial pressure

o MAP – point vascular function intercepts x axis
• Point there is no flow in the cardiovascular system
• Altered by an change in blood volume, change in venous capacitance
• Increase shifts curve to the right; decrease shifts to left

o Slope of venous return curve – resistance of arterioles

• Steeper curve – decrease in total peripheral resistance (TPR)
• Increased venous return
• Shallower curve – increase in TPR
• Decreased venous return

• Intersection – right atrial pressure
o Equilibrium point: CO = venous return

Question 22

Stroke volume

Answer 22

(End-diastolic volume) – (End-systolic volume)

Question 23

Cardiac output

Answer 23

Stroke volume X HR

Question 24

Ejection fraction

Answer 24

(Stroke volume)/(end-diastolic volume)

• Normal 55%