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BMS 752 (Medical Physiology) > ECG > Flashcards

ECG Flashcards

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USMLE® Step 1 flashcards
1
Q

what are the leads that should be placed for an ECG

A

right/left arm and leg

V1-6

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2
Q

where is V1

A

4th intercostal space to the right of the sternum

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3
Q

where is V2

A

fourth intercostal space at the left sternal border

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4
Q

where is V4

A

the midclavicular line at the 5th intercostal space

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5
Q

where is V3

A

midway between V4 and V2

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6
Q

where is V5

A

at the anterior axillary line in the 5th intercostal space

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7
Q

where is V6

A

at the midaxillary line at the 5th intercostal space

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8
Q

what forms ECG recordings

A

the electrical signals formed by action potentials in the heart

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9
Q

T/F a larger muscle will produce greater voltage and larger ECG waveform

A

true

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10
Q

scalar ECG

A

a recording of the potential differences between two points on the body surface

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11
Q

is an ECG an action potential?

elaborate

A

no

ECG reflects the cumulative effect of action potentials at skin level

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12
Q

what are the three main parts of an ECG wave

A

P wave

QRS complex

T wave

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13
Q

what electrical event does the P wave represent

A

atrial depolarization

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14
Q

what electrical event does the QRS complex represent

A

ventricular depolarization

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15
Q

what electrical event does the T wave represent

A

ventricular repolarization

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16
Q

why can’t you appreciate atrial repolarization on a normal ECG

A

because it is masked by the QRS

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17
Q

what part of an ECG would correspond with SA node firing

A

the isoelectric period prior to the P wave

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18
Q

at what point on an ECG would correspond with AV node firing

A

halfway through the P wave into the PR segment

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19
Q

what structures are depolarizing during the PR segment

A

AV node

Bundle of His

Bundle branches

Purkinje fibers

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20
Q

PR interval

A

the length between the begining of the P wave to the Q wave

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21
Q

PR segement

A

isoelectric portion of the ECG between the end of the P wave and the start of the QRS

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22
Q

what would a long PR segement indicate

A

slow AV conduction

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23
Q

ST segment

A

the isoelectric portion between the end of QRS and the start of the T wave

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24
Q

what two parts of the ECG should be isoelectric

A

PR segement and ST segment

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25
Q

what recordings are included on a 12 lead ECG

A

I, II, III

aVR, aVL, aVF

V1-6

26
Q

what two limbs are used in lead I?

what is the direction of the force?

A

right and left arms

from right to left

27
Q

what two limbs are used in lead II?

what is the direction of the wave

A

right arm and a leg

from the right arm down to the leg

28
Q

what limbs are used in lead III?

what is the direction of the wave

A

left arm and lower limb

down and to the right

29
Q

T/F the right arm is always a positive lead in ECG

A

false, it is always negative

30
Q

what are the Dipolar leads in ECG?

why are they called that

A

Leads I-III

because there will always be two leads, one will be more negative to reflect the passing of an AP wave

31
Q

what are the three augmented unipolar leads

A

aVL, aVR, aVF

32
Q

what is the direction of aVR

A

from the heart toward the right arm

33
Q

what is the direction of aVL

A

from the heart to the left arm

34
Q

what is the direction of aVL

A

from the heart towards the legs

35
Q

einthovens triangle

A

an imaginary triangle formed by the upper and lower limbs along with the pelvis used to measure the amplitude and direction of cardiac APs at the skin

36
Q

what would be considered a left axis devation?

what would cause that

A

a heart vector that is from 0 to -90 degrees

left ventricular hypertropy or inferior MI

37
Q

what would be considered right axis deviation?

what would cause this

A

heart axis shift to between 90 and 180 degrees

left bundle branch block, right ventricular hypertrophy

38
Q

how can a cardiac AP be considred a wave

A

there is a wavefront of depolarized cells followed by hyperpolarizing cellls

39
Q

what is the function of leads V1-6 on ECG

A

to observe the deoplarization wave in the frontal plane from a particular area of the heart

40
Q

what is the standard paper speed of an ECG

A

25mm/sec

41
Q

a standard paper speed, what are the x and y axes

A

x is time

y is voltage

42
Q

on a standard ECG what are the units on the x axis? y axis?

A

x axis = .04seconds per division

y axis = .1mV per division

43
Q

how should HR be calculated of ECG when the heart rate is constant

A

R-R distance

44
Q

describe the process of calculating heart rate using R-R interval

A

measure the distance in mm between consecutive R waves

divide the paper length in 60s (1500mm) by the RR length

45
Q

describe the process of calculating HR by RR interval

A

measure the interval of time between R waves

divide 60s by the RR time

46
Q

how should HR be calculated if the HR varies

A

count the number of RR intervals in 10 seconds and multiply by 6

47
Q

what is quick way to estimate HR on ECG if the rate is regular

A

1 space between R waves is 300bpm

2 = 150

3 = 100

4 = 75

5 = 60

48
Q

what should a normal sinus rhythm look like on ECG

A

positive P waves in the leads I and II indicate rhythm from the SA node

49
Q

what are three causes of arrhythmias

A

delayed after polarizations

conductions defects

circuit re-entry

50
Q

two examples of delayed after polarization

A

ectopic beats

PVCs

51
Q

two examples of conduction defects that would cause arrhythmias

A

heart block

bundle branch block

52
Q

what happens during circuit re-entry that causes arrhythmia

A

conduction from the ventricle is looped around to cause an abnormal conduction and stimulation pattern

53
Q

compensatory pause

what is the function

A

a prolonged isoelectric period following an ectopic beat and the resumption of sinus

allows the heart to reset

54
Q

heart block/bundle branch block

A

failure of the AV node to conduct from the atria to the ventricles

55
Q

what are two common causes of heart block

A

ischemic heart disease

valve fibrosis

56
Q

what will an ECG look like with heart block

A

normally firing P waves from the SA node with missing QRS complexes

57
Q

whatis ST segment depression/T wave inversion indicative of

A

signs of previous ischemia

58
Q

what starts a ventricular fibrillation

A

R on T firing

59
Q

R on T firing

A

ectopic APs that occur during the “vulnerable period” of the late T wave

60
Q

what causes ventricular fibrillation to persist

A

re-entry of AP into the circuit, causing repeating circus pathways

BMS 752 (Medical Physiology) (13 decks)

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