ECG (Quiz 2)

Question 1

True/false: when there is a cardiac impulse there is also an electrical current that spreads from the heart to surrounding tissue

Answer 1

true –> a small portion of the current spreads all the way to the surface of the body

Question 2

What is an electrocardiogram (ECG)

Answer 2

the recording of electrical potentials generated by the heart’s current –> through electrodes that are placed on the skin on opposite sides of the heart

Question 3

What kinds of information does an ECG provide?

Answer 3

heart’s electrical activity, rate, and rhythm
aka time and voltage

Question 4

how is depolarization read on an ECG?
… kinda long

Answer 4

1. depolarization: the normal negative potential inside the fiber reverses - becomes slightly positive on the inside and negative on the outside
2. ECG picks up on the negative charge outside of the fiber
3. the machine automatically flips so the graph reads what is happening inside of the fiber

Question 5

how long does a single action potential of ventricular muscle normally last? (depolarization + repolarization)

Answer 5

between 0.25 and 0.35 seconds

Question 6

What is a P wave? what causes it?

Answer 6

-the first bump on an ECG
-electrical potentials generated by atrial depolarization
**before atrial contraction begins

Question 7

What is the QRS complex? what causes it?

Answer 7

-flat line + positive and negative spikes on an ECG following the P wave
-potentials generated when the ventricles depolarize
**before contraction

Question 8

what is the T wave? what causes it?

Answer 8

-the last bump recorded on an ECG before the next P wave
-potentials generated as the ventricles recover (REPOLARIZATION)
**the only repolarization wave recorded

Question 9

how long is the average P-R interval? what does it represent?

Answer 9

-0.16 sec
-the time b/w bundle branches depolarizing

Question 10

what happens when the P-R interval decreases?

Answer 10

Heart rate increases and stroke volume decreases

Question 11

what does the Q-T interval represent?

Answer 11

ventricular contraction to repolarization

Question 12

why does depolarization happen before the contraction

Answer 12

because it takes take for the signal to initiate the chemical processes of contraction throughout the whole muscle
-still a pretty fast process though

Question 13

true/false: the ventricles remain contracted until after the repolarization has occurred

Answer 13

TRUE!
Another wording: ventricles remain contracted until the end of the T wave

Question 14

Reading an ECG:
what do the horizontal calibration lines represent?

Answer 14

voltage!
one square = 1mm = 0.10 mV
10 lines = 1 millivolt

Question 15

Reading an ECG:
what do the vertical calibration lines represent?

Answer 15

Time!
one square = 1mm = 0.04 sec
5 lines = 0.2 sec
25 = 1 min

Question 16

Where does depolarization start?

Answer 16

the SA node

Question 17

what is the Q wave?

Answer 17

-negative deflection
-slow waves that travel through the myocytes in the interventricular septum
-is negative bc it moves away from the leads

Question 18

What is the R-wave

Answer 18

-biggest spike
-depolarization of the purkinje fibers

Question 19

what is the S-wave?

Answer 19

-negative spike
-depolarization of the top of the ventricles
-is negative bc it moves away form the leads

Question 20

what is the S-T segment/interval?

Answer 20

-b/w s wave and t wave
-no electrical activity bc the ventricles are contracting and the atrials are filling

Question 21

What is the U-Wave

Answer 21

not seen on all ECGs*
-small after the T-wave, before the next cycle
-represents purkinje fiber repolarization

Question 22

Rate determination:
What is the box method?

Answer 22

1. counting the number of boxes b/w heart beats –> typically b/w the apex of the R-waves
2. MATH!
   –> 1 box = 0.04 sec
   Equation: 1/time = x/60 sec
   x=beats