EKG and the Cardiac Cycle

Question 1

Non contractile cells are called what?

Answer 1

Pacemakers cells (autorythmic)

Question 2

Contractile cells

Answer 2

responsible for the heart’s pumping function

like skeletal muscle, depolarization precedes contraction

unlike skeletal muscle, action potentials in cardiac muscle cells have a characteristic hump/plateau

Question 3

What is most of the heart made up of?

Answer 3

Contractile cells

Question 4

3 steps of cardiac action potential

Answer 4

1. depolarization: open fast sodium (Na+) channels, extracellular Na+ enter

rising phase of action potential (-90mV to +30mV)

influx of Na+ will stop quickly

2. voltage change opens calcium (Ca2+) channels, influx of extracellular Ca2+

Ca2+ influc prolongs depolarization - the plateau

cells will contract as long as Ca2+ entering

3. Repolarization: results from inactivated Ca2+ channels, the opening of the potassium (K+) channels - an efflux pf K+

resting potential (-70mV) is restored

Ca2+ is either pumped out of the cell or into the sarcoplasmic reticulum

Question 5

Functions of Plateau

Answer 5

Both the action potential and the contraction phase longer in cardiac muscle than skeletal muscle

Sustained contraction ensures efficient ejection of blood from the ventricles

Longer absolute refractory period avoids tetany

Question 6

Electrocardiography

Answer 6

the electrical currents generated in and transmitted through the body can be detected

graphic recording of heart’s cavity

has 3 distinguishable waves or deflections

Question 7

P Wave

Answer 7

Last .08s

Results from movement of the depolarization waves from SA to AV Node

the atria contract .1s after the P Wave begins

Question 8

QRS Complex

Answer 8

Last .08s

Results from ventricular depolarization, precedes ventricular contraction

Question 9

T Wave

Answer 9

Last .16s

Results from ventricular repolarization

Question 10

When does atrial repolarization occur?

Answer 10

During ventricular depolarization - the resultant wave was obscurred by the QRS complex

Question 11

Interval

Answer 11

duration of time that includes 1 segment and 1+ wave

Question 12

Segment

Answer 12

region between two waves

Question 13

P-R interval

Answer 13

.16 s - the beginning of atrial depolarization to the beginning of ventricular depolarization

Question 14

S-T segment

Answer 14

action potentials of ventricular myocytes are in plateau, the entire ventricular myocardium is depolarized

an elevated or depressed ST segment can indicate cardiac ischemia

Question 15

Atrial Depolarization

Answer 15

Completed by SA Node, causes P Wave

Question 16

Atrial Depolarization Complete

Answer 16

impulse delayed at Av Node

Question 17

Ventricular Depolarization

Answer 17

begins at apex, causes QRS complex

atrial repolarization occurs, but is obscurred

Question 18

Ventricular repolarization

Answer 18

begins at apex, causes T Wave

Question 19

the cardiac cycle is … events of the heart

Answer 19

mechanical

Question 20

Systole

Answer 20

contraction

blood is forced out of the heart’s chamber

Question 21

Diastole

Answer 21

relaxation

blood refills the heart’s chambers

Question 22

Steps of cardiac cycle

Answer 22

1. Vetricular filling:

• pressure is low, blood flows from atria to vetricles
• AV valves are open, SL valves are closed
• responsible for 80% of ventricular filling
• following atrial depolarization (P Wave), atrial systole occur, and blood is compressed into the ventricles
• end diastolic volume (EDV): the maximum volume of blood that the ventricles will contain the cardiac cycle
• atrial diastole and the start of the ventricular depolarization

Question 23

cardiac cycle step 2 (Isovolumetric contraction)

Answer 23

• atria relax slide 16 + 17

Question 24

flow of blood through the heart is governed by …

Answer 24

pressure changes - blood always follows down a pressure gradient (high -> low)

Question 25

restarting the cardiac cycle

Answer 25

while the ventricles are contracting in systole, the atria are diastole and filling

when the pressure in the filling atria exceeds the pressure in the ventricles, the AV valves open, and ventricular filling begins again

1 cardiac cycle - .8s

atrial systole - .1s
ventricular systole - .3s
quiescent period - .4s

Question 26

Pulmonary Circulation

Answer 26

low pressure circuit - pressure in the pulmonary arteries = 24/20 mmHg

Question 27

Systemic circulation

Answer 27

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

Question 28

both sides of the heart eject…

Answer 28

the same volume of blood with each beat

Question 29

How many sounds are heard with each heartbeat?

Answer 29

two sounds

Question 30

1st sound

Answer 30

Av valves closing

• start of ventricular systole
• longer, louder sound

Question 31

2nd sound

Answer 31

AL valves closing

• start of ventricular diastole
• shorter, sharper sound

Question 32

Murmur

Answer 32

abnormal heart sound secondary to turbulent blood flow

more common in children and elderly people; thin walled hearts allow more vibration

can indicate of a valve problem - insufficient or incompetent valves allowing regurgitation or back flow