17-3: EKG and the Cardiac Cycle

Question 1

electrocardiogram

Answer 1

impulses transmitted through the conduction system cause electrical currents that can be detected on the body’s surface with an electrocardiograph

Question 2

P wave

Answer 2

first small upward curve, indicates atrial depolarization (spread of impulse from SA node through atria)

Question 3

QRS complex

Answer 3

downward deflection (Q - impulse to apex) followed by large upright triangular wave (R), ending in second downward deflection (S). Indicates ventricular depolariation (spread of impulse through the ventricles)

Question 4

T wave

Answer 4

dome-shaped upward curve; indicates ventricular repolarization (atrial repolarization wave is hidden by QRS wave)

Question 5

reading the EKG

Answer 5

changes in timing or pattern of the EKG may reveal a diseased or damaged heart

Question 6

enlarged P wave

Answer 6

enlarged atria, as in mitral stenosis (a narrow valve causes blood to back up into the atrium, causing it to enlarge)

Question 7

PQ interval

Answer 7

the time required for the impulse to travel through the atria and AV node to the ventricles

Question 8

longer PQ interval

Answer 8

may be due to scars or inflammation

Question 9

enlarged Q wave

Answer 9

may indicate myocardial infarction

Question 10

enlarged R wave

Answer 10

indicates enlarged ventricles (eg. lung disease)

Question 11

shorter ST segment

Answer 11

heart is getting low O2

Question 12

flattened T wave

Answer 12

cardiac ischemia (insufficient blood flow in coronary vessels)

Question 13

elevated T wave

Answer 13

hyperkalemia (potessium levels are high)

Question 14

cardiac cycle

Answer 14

sequences of events in one heartbeat (about 0.8 seconds)

Question 15

systole

Answer 15

contraction

Question 16

diastole

Answer 16

relaxation

Question 17

complete diastole

Answer 17

all chambers are relaxed, pressure in the heart is low

Question 18

In complete diastole, ___ blood flows into __, and __ blood flows into ___.

Answer 18

deoxy; right atrium from SVC, IVC, and coronary sinus; oxy; left atrium from pulmonary veins

Question 19

What causes the AV valves to open?

Answer 19

increasing blood flow into the atria causes the atrial pressure to rise above ventricular pressure, causing the AV valves to open

Question 20

period of ventricular filling

Answer 20

with AV valves open, 70-80% of blood flows passively from atria to ventricles

Question 21

What happens after the period of ventricular filling?

Answer 21

SA node fires, and the impulse spreads over the atria; atrial depolarization - P wave

Question 22

atrial systole

Answer 22

contraction of the atria

Question 23

What causes atrial systole?

Answer 23

spread of the impulse from the SA node causes the 2 atria to contract simultaneously, forcing the remaining blood into the ventricles

Question 24

After atrial systole, the impulse ___.

Answer 24

reaches the AV node, travels down the bundle of His into the ventricular walls, creating the QRS wave (ventricular depolarization)

Question 25

ventricular systole

Answer 25

contraction of the ventricles

Question 26

What creates the first heart sound?

Answer 26

as the atria relax, the ventricles begin to contract, causing an abrupt rise in ventricular pressure, causing the AV valves to close

Question 27

isovolumetric contraction phase

Answer 27

period in ventricular systole with all valves closed

Question 28

During ventricular systole, the continuing rise in pressure causes ___, and blood ___.

Answer 28

the SL valves to open; is forced out into the large arteries leaving the heart (ventricular ejection)

Question 29

During ventricular systole, the atria ___.

Answer 29

are relaxed and starting to fill with blood

Question 30

quiescent period

Answer 30

return to diastole after ventricular systole and ejection

Question 31

What causes the second heart sound?

Answer 31

After ventricular ejection, the pressure in the ventricles decreases rapidly and blood in the aorta and pulmonary trunk starts to flow back; this causes the SL valves to close and create the second heart sound

Question 32

isovolumetric relaxation phase

Answer 32

all valves are closed, and all chambers relaxed; the atria have begun filling with blood, and eventually the increased atrial pressure will cause the AV valves to open

Question 33

The isovolumetric relaxation phase ends in the period ___.

Answer 33

of ventricular filling, when the AV valves open due to increased pressure in the atria