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Physiology Exam 2 > L8: Heart Rhythmicity & EKG > Flashcards

L8: Heart Rhythmicity & EKG Flashcards

1
Q

timing of signal conductance from SA to ventricles

A

SA — > AV 0.3
delayed 0.9
delayed in bundles 0.4

reaches ventricles 0.16 after origin

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2
Q

factors that cause slow/delayed conduction

A

small cell size
low amplitude
slow depolarization rates

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3
Q

SA node resting potential and threshold

A
  • 55 to -60

- 40mV

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4
Q

fast Na channels: rest to AP

A

inactive at rest
inactivation gate closes when less < -55
activation gate opens at -40
inactivation gate closes 100-150msec after opening

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5
Q

slow Na channels: rest to AP

A

are open/leaky at rest

causes slow depolarization/repolarization

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6
Q

K+ channels: rest to AP

A

open when Na/Ca channels inactivate +20

nodal cells slowly repolarize
channels remain open
efflux of K+

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7
Q

ventricular fiber resting potential

A

-85 to -90

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8
Q

sinus rhythm

A

SA generating AP

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9
Q

ectopic focus

A

any other region of the heart generating an action potential besides the normal SA AP

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10
Q

how can the AP and heart rate be modulated?

A

vagus nerve - ACH

sympathetic - Norepinephrine

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11
Q

vagus nerve stimulation

A

mainly to SA/AV nodes

activates ACH

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12
Q

response to vagus nerve stimulation

A

decrease SA rate and excitability of SA/fibers

increase permeability of fiber membranes to K+ ions
K+ efflux - cell becomes more negative
results in hyperpolarization

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13
Q

hyperpolarization numbers

A

normal -65 to -70

hyper -55 to -60

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14
Q

a substance that causes a decrease in heart rate

A

negative chronotropic effect

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15
Q

a substance that causes an increase in heart rate

A

positive chronotropic effect

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16
Q

sympathetic stimulation

A

to all parts of the heart
mainly ventricles

neurotransmitter: norepinephrine

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17
Q

response to sympathetic stimulation

A

stimulates beta-1 adrenergic receptors
increase depolarization rates

increase permeability of fiber membranes to Na and Ca
leak into cell = more easily excitable

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18
Q

result of sympathetic stimulation

A

increased HR

increased contractile power of ventricles

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19
Q

atrial depolarization and contraction

A

P wave

phase 0 of atria

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20
Q

ventricle depolarization and contraction

A

QRS complex

phase 0 of ventricles

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21
Q

ventricle repolarization

A

occurs at the end of T wave

phase 3 of ventricles

22
Q

atrial repolarization

A

hidden by QRS-T waves

23
Q

how does an EKG differ from the recordings of TM potentials?

A

EKG is a graphic representation of electrical activity in cardiac muscle tissue

TM potential recorded from an axon

24
Q

when does deflection from 0 occur in an EKG

A

when current is flowing between regions of heart

current only flows when regions are partly polarized

no potential is ever recorded when regions are fully polarized or depolarized

25
Q

under what conditions does current flow or not flow?

A

current flows negative to positive

only flows when regions are partly de-/re-polarized

26
Q

P-Q interval

A

also called P-R
P to beginning of QRS

0.16sec

27
Q

Q-T interval

A

0.35 sec

28
Q

___ bipolar limb ____

A

3 bipolar limb leads
I
II
III

29
Q

limb lead l

A 
neg = right wrist
pos = left wrist

looks at heart from right to left
vector = 0 degrees

30
Q

limb lead ll

A 
neg = right wrist
pos = left ankle

looks at heart from upper right to apex
vector = 60 degrees

31
Q

limb lead lll

A 
neg = left wrist
pos = left ankle

looks at heart from upper left to apex
vector = 120 degrees

32
Q

current in the heart flows from ____ to ____ primarily from base to apex, until ….?

A

from negative to positive

until the very end

33
Q

list the recordings of each lead as negative or positive?

A

all 3 record positive

34
Q

what is Einthoven’s triangle?

A

the triangle formed by the 3 bipolar limb leads

35
Q

if the electrical potentials of any two of the three bipolar limb leads are known at any given instant, the third can be determined by summing the first two.

A

Einthoven’s law

36
Q

define vector

A

an arrow that points in the direction of the electrical potential generated by flow of current

arrow always points towards positive

length of arrow is determined by size/strength of current

37
Q

voltages readings: effect of direction in relation to triangle

A

vector is perpendicular to axis of lead
–EKG is very low

same axis
–entire voltage recorded

horizontal vector = horizontal

38
Q

summated vector of the generated potential at a particular instant

A

instantaneous mean vector

39
Q

QRS vector

A

mean electrical axis of heart
+59 degrees

average vector during depolarization thru ventricles

40
Q

abnormal ventricular conditions that cause deviation from mean

A 
change in position of heart in chest
hypertrophy
bundle block
fluid in pericardium
pulmonary emphysema
41
Q

most common cause of a high voltage EKG

A

hypertrophy of the ventricle

42
Q

when does a high voltage EKG occur

A

when the sum of the voltages of all the QRS complexes in the 3 leads in >4mV

43
Q

causes of decreased voltage EKG

A

conditions surrounding the heart

cardia myopathies

44
Q

normal QRS timing

A

0.06 to 0.08

45
Q

QRS timing in hypertrophy

A

also dilation/prolonged

0.09 to 0.12

46
Q

conditions causing bizarre patterns of QRS

A

destruction of cardiac muscle and replaced with scar tissue

multiple small local blocks in the conduction impulses of the purkinje system

47
Q

different cardiac abnormalities cause part of the heart to remain depolarized all the time

A

currents of injury

48
Q

causes of currents of injury

A

mechanical trauma
infectious processes
ischemia**

49
Q

most common cause of currents of injury

A

ischemia

50
Q

reference point for analyzing current of injury

A

J point

the 0 line on the vertical axis

Physiology Exam 2 (9 decks)

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