ECG Flashcards
electrical signal through heart
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
what is the cardiac muscle made up of
nucleus, mitochondria, myosin, actin, sarcolemma and sarcoplasmic reticulum
what is the concentration of mitochondria
20-45% depending on training status
role of sarcolemma
binds structure together
role of sarcoplasmic reticulum
stores calcium
role of intercalated discs
allows myocytes to lock together
large surface area
interdigtation - stronger binding
role of desmosomes
help provide extra strength to binding
role of gap junctions
allows quick conduction of ions and metabolities between two myocytes
movement down conc gradient
what are autorhymtic cells
generates action impluse by themselves
autorhytmic BPM of SA node
approx 90-100
autorhytmic BPM of AV node
approx 40-60
autorhytmic BPM of bundle of his
15-30
describe cardiac action potential at rest
more NA+ and Ca+ outside
more K+ inside
resting potentail of -70mv
describe pacemaker action potential
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
describe contracil myocytes action potential
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
Ca pathway in contracting muscle
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+
how much of Ca2+ is receyled into SR
70%
how many Ca2+ exchanged for Na
1 Ca2+ for 3 Na+
what is the refractory period
time it takes for the cell to reset itself
refractory period in cardiac
longer than skeletal
almost same length as muscle contraction
unable to recieve another signal until fully relaxed
prevents tetanus
resting and AP of SA node
-50mv
0mv
resting and AP of atria
-75mv
+30mv
resting and AP of AV node
-60mv
0mv
resting and AP of purkinje fibres
-90mv
+40mv
resting and AP of ventricles
-80mv
+30mv
size of each big sqaure on ECG trace
0.2 secs
size of each small sqaure on ECG trace
0.04 secs
use of ECG
HR conduction in heart arrythimas damage to heart provides no info about pumping or mechanical events
what are the 10 steps in ECG
rate rhythm axis p wave pr interval QRS complex ST segment T wave U wave QT interval
calculating rate
can use the squares
1 large = 300bts/min
count no of squares between peak
calculating rhythm
can eye ball first, look at spacing between p waves
is it in the correct order
morphology of P wave
smooth contour
monophase in lead II
biphasic in VI
upside down in AVR
duration of P wave
<120ms
1-2 small squares
amplitude of P wave
<2.5mm in the limb leads
size of QRS complex
<0.12
3 small squares
ventricular hypertrophy in QRS
increased height
caused by increase in muscle mass in either verntricle
why do we get the shape of the q wave
LBB depolarizes first, then RBB
downward deflection
positive wave, moves right through spetum
less that 0.4 seconds
QRS shape in lead II
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
St segments
beginning of St segment called j point
represents first uprupt right-ward direction of trace
changes during exercise
t wave
ventricular repolarisation
apmlitude <5mm in limb, <10mm in chest leads
what is the direction of ventricle depolarsation
endo -> epicardium
what is the direction of ventricle repolaristion
epi -> endocardium
u wave
reploarization of purkinje
often not seen
should be less than 25% of T `
QT interval
represents the time of depolarisation and reploarisation
varies inversley with HR so needs to be corrected to account for this
QT correction formula
bazetts formula
QTc = QT interval/sqr(r to r interval)
shoudl be 0.35 - 0.45 secs
