EKG and the Cardiac Cycle

Question 1

3 steps of Cardiac Action Potential (1st step)

Answer 1

Depolarization- opens fast sodium (Na+) channels, extracellular Na+ enters

• rising phase of action potential (-90mV to +30mV)
• influx of Na+ will stop quickly

Question 2

3 steps of Cardiac Action Potential (2nd step)

Answer 2

Voltage change open calcium Ca2+ channels, influx of extracellular Ca2+

-Ca2+ influx prolongs depolarization - the plateau
- cells will contract as long as Ca2+ is entering

Question 3

3 steps of Cardiac Action Potential (3rd step)

Answer 3

repolarization- results from inactivated Ca2+ channels, the opening of potassium K+ channels - an efflux of K+

• resting potential (-70mV) is restored
• Ca 2+ is either pumped out of the cell or into the sarcoplasmic reticulum

Question 4

Function of Plateau

Answer 4

• Action potential and contraction phase are longer in cardiac muscle
• sustained contraction ensures efficient ejection of blood from the ventricles
• longer absolute refractory period avoids tetany

Question 5

P Wave

Answer 5

• Last .08s
• results from movement of the depolarization wave from SA to AV node
• the atria contracts .1s after the P wave begins

Question 6

QRS complex

Answer 6

• lasts .08s
• results from ventricular depolarization, precedes ventricular contraction

Question 7

T wave

Answer 7

• lasts .16s
• results from ventricular repolarization

Question 8

Why is atrial repolarization not seen on a typical EKG?

Answer 8

Atrial repolarization occurred during ventricular depolarization – the resultant wave was obscured by the QRS Complex

Question 9

Interval

Answer 9

duration of the time that includes 1 segment and 1+ wave

Question 10

Segment

Answer 10

a region between two waves

Question 11

What is the possible clinical significance of an elevated or depressed ST segment?

Answer 11

Cardiac ischemia

Question 12

Atrial Depolarization

Answer 12

Completed by SA Node, causes P wave

Question 13

Atrial depolarization complete

Answer 13

Impulse delayed at AV Node

Question 14

Ventricular Depolarization

Answer 14

• Begins at apex, causes QRS complex
• Atrial repolarization occurs, but is obscured

Question 15

Ventricular repolarization

Answer 15

Begins at apex, causes T wave

Question 16

Systole

Answer 16

• Contraction
• Blood is forced out the heart’s chambers

Question 17

Diastole

Answer 17

• Relaxation
• Blood refills the heart’s chambers

Question 18

Cardiac Cycle (1st step)

Answer 18

Ventricular Filling
- pressure is low, blood flows from atria to ventricles
- AV valves open, SL valves close
- 80% of ventricular filling
- following atrial depolarization (P Wave), atrial systole occurs, and blood is compressed into the ventricles
- EDV
- atrial diastole and the start of ventricular depolarization

Question 19

Cardiac Cycle (2nd step)

Answer 19

Isovolumetric Contraction
- atria relax, ventricles start contracting, pressure in ventricles rises
- AV valves close
- for a moment, the ventricles are closed chambers with a constant blood volume
- pressure continues to rise until it exceeds the pressure in the great vessels
- SL valves open

Question 20

Cardiac Cycle (3rd step)

Answer 20

Ventricular Ejection
- blood moves from the ventricles to the great vessels (pulmonary trunk vs aorta)
- pressure in the aorta is typically - 120mmHg

Question 21

Cardiac Cycle (4th step)

Answer 21

Isovolumetric Relaxation
- following the T-wave, the ventricles relax
- ESV
- ventricular pressure drops, blood slides from the great vessels back towards the ventricles - SL valves close
- ventricles are again closed chambers

Question 22

End Diastolic Volume (EDV)

Answer 22

the maximum volume of blood that the ventricles will contain in the cardiac cycle

Question 23

End Systolic Volume (ESV)

Answer 23

the un-ejected blood remaining in the ventricular chambers

Question 24

Dicrotic Notch

Answer 24

a brief rise in aortic pressure caused by blood rebounding off the newly closed aortic valve (isovolumetric Relaxation)

Question 25

Pulmonary Circulation

Answer 25

low-pressure circuit - pressure in the pulmonary arteries = 24/10 mmHg

Question 26

Systemic Circulation

Answer 26

higher-pressure circuit - pressure in the aorta = 120/80 mmHg

Question 27

Closure of the ____ Valves is the 1st Sound (“lub”)

Answer 27

AV

Question 28

Closure of the ____ Valves is the 2nd Sound (“dup”)

Answer 28

SL

Question 29

Murmur

Answer 29

an abnormal heart sound secondary to turbulent blood flow