L8: Heart Rhythmicity & EKG

Question 1

timing of signal conductance from SA to ventricles

Answer 1

SA — > AV 0.3
delayed 0.9
delayed in bundles 0.4

reaches ventricles 0.16 after origin

Question 2

factors that cause slow/delayed conduction

Answer 2

small cell size
low amplitude
slow depolarization rates

Question 3

SA node resting potential and threshold

Answer 3

• 55 to -60

- 40mV

Question 4

fast Na channels: rest to AP

Answer 4

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

Question 5

slow Na channels: rest to AP

Answer 5

are open/leaky at rest

causes slow depolarization/repolarization

Question 6

K+ channels: rest to AP

Answer 6

open when Na/Ca channels inactivate +20

nodal cells slowly repolarize
channels remain open
efflux of K+

Question 7

ventricular fiber resting potential

Answer 7

-85 to -90

Question 8

sinus rhythm

Answer 8

SA generating AP

Question 9

ectopic focus

Answer 9

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

Question 10

how can the AP and heart rate be modulated?

Answer 10

vagus nerve - ACH

sympathetic - Norepinephrine

Question 11

vagus nerve stimulation

Answer 11

mainly to SA/AV nodes

activates ACH

Question 12

response to vagus nerve stimulation

Answer 12

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

Question 13

hyperpolarization numbers

Answer 13

normal -65 to -70

hyper -55 to -60

Question 14

a substance that causes a decrease in heart rate

Answer 14

negative chronotropic effect

Question 15

a substance that causes an increase in heart rate

Answer 15

positive chronotropic effect

Question 16

sympathetic stimulation

Answer 16

to all parts of the heart
mainly ventricles

neurotransmitter: norepinephrine

Question 17

response to sympathetic stimulation

Answer 17

stimulates beta-1 adrenergic receptors
increase depolarization rates

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

Question 18

result of sympathetic stimulation

Answer 18

increased HR

increased contractile power of ventricles

Question 19

atrial depolarization and contraction

Answer 19

P wave

phase 0 of atria

Question 20

ventricle depolarization and contraction

Answer 20

QRS complex

phase 0 of ventricles

Question 21

ventricle repolarization

Answer 21

occurs at the end of T wave

phase 3 of ventricles

Question 22

atrial repolarization

Answer 22

hidden by QRS-T waves

Question 23

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

Answer 23

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

TM potential recorded from an axon

Question 24

when does deflection from 0 occur in an EKG

Answer 24

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

Question 25

under what conditions does current flow or not flow?

Answer 25

current flows negative to positive only flows when regions are partly de-/re-polarized

Question 26

P-Q interval

Answer 26

also called P-R P to beginning of QRS 0.16sec

Question 27

Q-T interval

Answer 27

0.35 sec

Question 28

___ bipolar limb ____

Answer 28

3 bipolar limb leads I II III

Question 29

limb lead l

Answer 29

``` neg = right wrist pos = left wrist ``` looks at heart from right to left vector = 0 degrees

Question 30

limb lead ll

Answer 30

``` neg = right wrist pos = left ankle ``` looks at heart from upper right to apex vector = 60 degrees

Question 31

limb lead lll

Answer 31

``` neg = left wrist pos = left ankle ``` looks at heart from upper left to apex vector = 120 degrees

Question 32

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

Answer 32

from negative to positive until the very end

Question 33

list the recordings of each lead as negative or positive?

Answer 33

all 3 record positive

Question 34

what is Einthoven's triangle?

Answer 34

the triangle formed by the 3 bipolar limb leads

Question 35

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.

Answer 35

Einthoven's law

Question 36

define vector

Answer 36

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

Question 37

voltages readings: effect of direction in relation to triangle

Answer 37

vector is perpendicular to axis of lead --EKG is very low same axis --entire voltage recorded horizontal vector = horizontal

Question 38

summated vector of the generated potential at a particular instant

Answer 38

instantaneous mean vector

Question 39

QRS vector

Answer 39

mean electrical axis of heart +59 degrees average vector during depolarization thru ventricles

Question 40

abnormal ventricular conditions that cause deviation from mean

Answer 40

``` change in position of heart in chest hypertrophy bundle block fluid in pericardium pulmonary emphysema ```

Question 41

most common cause of a high voltage EKG

Answer 41

hypertrophy of the ventricle

Question 42

when does a high voltage EKG occur

Answer 42

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

Question 43

causes of decreased voltage EKG

Answer 43

conditions surrounding the heart | cardia myopathies

Question 44

normal QRS timing

Answer 44

0.06 to 0.08

Question 45

QRS timing in hypertrophy

Answer 45

also dilation/prolonged | 0.09 to 0.12

Question 46

conditions causing bizarre patterns of QRS

Answer 46

destruction of cardiac muscle and replaced with scar tissue multiple small local blocks in the conduction impulses of the purkinje system

Question 47

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

Answer 47

currents of injury

Question 48

causes of currents of injury

Answer 48

mechanical trauma infectious processes ischemia**

Question 49

most common cause of currents of injury

Answer 49

ischemia

Question 50

reference point for analyzing current of injury

Answer 50

J point | the 0 line on the vertical axis