ECG

Question 1

electrical signal through heart

Answer 1

SA node - pacemaker 
travels  along posterior, middle and anterior internodal tracts 
right atrium contracts 
backmans bundle fast tracts signal to left
contracts at same time 
signal meets again at AV node 
spreads down bundle his 
at apex, seperates into pjunke fibres 
ventricles contracts

Question 2

what is the cardiac muscle made up of

Answer 2

nucleus, mitochondria, myosin, actin, sarcolemma and sarcoplasmic reticulum

Question 3

what is the concentration of mitochondria

Answer 3

20-45% depending on training status

Question 4

role of sarcolemma

Answer 4

binds structure together

Question 5

role of sarcoplasmic reticulum

Answer 5

stores calcium

Question 6

role of intercalated discs

Answer 6

allows myocytes to lock together
large surface area
interdigtation - stronger binding

Question 7

role of desmosomes

Answer 7

help provide extra strength to binding

Question 8

role of gap junctions

Answer 8

allows quick conduction of ions and metabolities between two myocytes
movement down conc gradient

Question 9

what are autorhymtic cells

Answer 9

generates action impluse by themselves

Question 10

autorhytmic BPM of SA node

Answer 10

approx 90-100

Question 11

autorhytmic BPM of AV node

Answer 11

approx 40-60

Question 12

autorhytmic BPM of bundle of his

Answer 12

15-30

Question 13

describe cardiac action potential at rest

Answer 13

more NA+ and Ca+ outside
more K+ inside
resting potentail of -70mv

Question 14

describe pacemaker action potential

Answer 14

no resting potential threshold at -40mv
funny channels open below -40mv - allows slow influx of Na+
at threshold - Ca2+ channels open, depolarisation
at peak - K+ channels open, Ca channels inactive
voltage returns to -60mv

Question 15

describe contracil myocytes action potential

Answer 15

resting at -90mv, only depolarise when stimulated
threshold of -70mv
fast Na channels open - rapid depolarisation
-40mv - L-type/slow Ca2+ channels open - slow steady influx
at peak - Na+ close, K+ open, Ca2+ stay open balance K = plateau
Ca induces greater influx of Ca = contraction
Ca channels close, K open
return to resting, pumps return balance

Question 16

Ca pathway in contracting muscle

Answer 16

depolarising wave from adjacent cell 
volatge gated CA2+ channels open, enters cell
Ca2+ induces Ca2+ release from R via ryanodine receptor 
local release casue Ca2+ spark 
summed spark creates a Ca2+ signal 
Ca2+ ions bind to tropoin = contraction 
relaxation - Ca2+ unbinds
pumped back into SR via ATP pump
exchanges with Na+

Question 17

how much of Ca2+ is receyled into SR

Answer 17

70%

Question 18

how many Ca2+ exchanged for Na

Answer 18

1 Ca2+ for 3 Na+

Question 19

what is the refractory period

Answer 19

time it takes for the cell to reset itself

Question 20

refractory period in cardiac

Answer 20

longer than skeletal
almost same length as muscle contraction
unable to recieve another signal until fully relaxed
prevents tetanus

Question 21

resting and AP of SA node

Answer 21

-50mv

0mv

Question 22

resting and AP of atria

Answer 22

-75mv

+30mv

Question 23

resting and AP of AV node

Answer 23

-60mv

0mv

Question 24

resting and AP of purkinje fibres

Answer 24

-90mv

+40mv

Question 25

resting and AP of ventricles

Answer 25

-80mv

+30mv

Question 26

size of each big sqaure on ECG trace

Answer 26

0.2 secs

Question 27

size of each small sqaure on ECG trace

Answer 27

0.04 secs

Question 28

use of ECG

Answer 28

HR
conduction in heart 
arrythimas
damage to heart 
provides no info about pumping or mechanical events

Question 29

what are the 10 steps in ECG

Answer 29

rate 
rhythm 
axis
p wave 
pr interval 
QRS complex 
ST segment
T wave 
U wave 
QT interval

Question 30

calculating rate

Answer 30

can use the squares
1 large = 300bts/min
count no of squares between peak

Question 31

calculating rhythm

Answer 31

can eye ball first, look at spacing between p waves

is it in the correct order

Question 32

morphology of P wave

Answer 32

smooth contour
monophase in lead II
biphasic in VI
upside down in AVR

Question 33

duration of P wave

Answer 33

<120ms

1-2 small squares

Question 34

amplitude of P wave

Answer 34

<2.5mm in the limb leads

Question 35

size of QRS complex

Answer 35

<0.12

3 small squares

Question 36

ventricular hypertrophy in QRS

Answer 36

increased height

caused by increase in muscle mass in either verntricle

Question 37

why do we get the shape of the q wave

Answer 37

LBB depolarizes first, then RBB
downward deflection
positive wave, moves right through spetum
less that 0.4 seconds

Question 38

QRS shape in lead II

Answer 38

q wave - depolarise left to right, away from electrode giving negative wave
R wave - moves toward electrode, down septum giving strong positive wave
R and L ventricle depolarise together cancelling each other out thus the line returns
S wave - L ventricle is slgithly large to depolarise last longer

Question 39

St segments

Answer 39

beginning of St segment called j point
represents first uprupt right-ward direction of trace
changes during exercise

Question 40

t wave

Answer 40

ventricular repolarisation

apmlitude <5mm in limb, <10mm in chest leads

Question 41

what is the direction of ventricle depolarsation

Answer 41

endo -> epicardium

Question 42

what is the direction of ventricle repolaristion

Answer 42

epi -> endocardium

Question 43

u wave

Answer 43

reploarization of purkinje
often not seen
should be less than 25% of T `

Question 44

QT interval

Answer 44

represents the time of depolarisation and reploarisation

varies inversley with HR so needs to be corrected to account for this

Question 45

QT correction formula

Answer 45

bazetts formula
QTc = QT interval/sqr(r to r interval)
shoudl be 0.35 - 0.45 secs