ECG Flashcards
ECG
measures dynamic changes in membrane potential
recording of small extracellular signals produced by movement of APs through cardiac myocytes
ECG measures movement of positive charge
propagating depolarization
upwards deflection
depolarization moving towards the electrode
downwards deflection
depolarization away from the electrode
repolarization
toward the electrode
lead
difference in voltage
each lead looks at the heart from a unique angle and plane
bipolar leads
3 bipolar limb leads
looks at heart in vertical plane
einthoven’s triangle
body is an electrical “volume conductor”
output: voltage difference provides a direct representation of heart’s electrical activity in that lead
unipolar leads
3 augmented voltage limb leads
6 precordial or chest leads
measures the electrical potential at one electrode relative to a reference point (often a central terminal)
augmented voltage
circle of axes and einthoven’s triangle
have no negative pole
output: each lead records the potential at one electrode compared to a calculated average of the other two limb electrodes
standard bipolar leads
lead 1: RA- to LA +
lead 2: RA- to LL+ (views conducting system)
lead 3: LA- to LL+
einthoven’s law
lead 1+lead 3= lead 2 (like vectors)
advantages of ECG
simple and cheap
info about:
- anatomical orientation of heart
- chamber sizes
- arrhythmias and conduction blocks (is heart conducting normally)
- myocardial ischaemia (is heart getting enough blood)
- myocardial infarction
- congenital defects (abnormalities)
- changes in cardiac function with time/therapy
standard unipolar leads
aVR: RA +ve, (LA+LL) -ve
aVL: LA +ve, (RA+LL) -ve
aVF: LL +ve, (LA+RA) -ve
depolarization away from lead
negative deflection
depolarization toward lead
positive deflection
repolarization away from lead
positive deflection
repolarization towards lead
negative deflection
chest leads unipolar “precordial”
view heard from horizontal plane
provides a view of the hearts electrical activity from a horizontal plane
provides info about specific areas of heard - good for diagnosing cardiac conditions
takes average of the three limb electrodes
standard chest leads
add
V1 and V2 = septal
V3 and V4 = anterior
V5 and V6 = lateral
subtract
take average mean (1,2,3) = center of heart
frontal plane leads
lead 1,2,3
aVL,aVR,aVF
transverse plane leads
V1-V6
what does each type of leads show us
scalar (1D) projection in that plane of the 3-D vector
12 leads allow us to reconstruct the amplitude and direction of this vector
right axis deviation
RV hypertrophy
infants
tall and thin
left posterior hemiblock
left axis deviation
obesity
pregnancy
left anterior hemiblock
LV hypertrophy
extreme axis
dextrocardia
cardiac pacemaker
sinus rhythm
normal heart rhythm
HR driven by SA node
depolarization along normal conduction path
subtle changes in HR occurs with each respiratory cycle (inspiration accelerated HR, expiration slows) - deepining of respirations accelerates these changes
loss of this rhythm may be seen in diabetes
types of altered sinus
mechanisms that vary the firing frequency of the cardiac pacemaker cells
pp interval is altered
bradycardia
Tachycardia
respiratory sinus arrythmia
tachycardia
increases HR
bradycardia
decreases HR
respiratory sinus arrythmia
breathing changes alters vagus nerve output
atrioventricular conduction blocks
block between AVN and perkinji fibres
premature depolarizations
extrasystoles - coupled to normal AP, re-entrant pathway, comes out of no where
occurs occasionally in most normal individuals - common in certain abnormal conditions
ectopic tachycardias
sporadic
ectopic pacemaker
AP in a re-entry loop
begins and ends abruptly, could be a few beats or for hours, days ( and they often reoccur)
happens in ventricles, but more commonly in atria
fibrillation
real trouble
atrial or ventricular - jiggles (not pumping)
multiple re-entry loops
uncoordinated contraction - insufficient pumping of blood
irregular type of contractions is inefficient in propelling blood
probably represents a re-entry phenomenon
not pumping blood to the rest of the body
right bundle branch block
no organized ventricle repolarizing
wide QS
slurred S in lateral leads
altered T in septal leads
acute anterior infarction
in front of heart tissue blocked
increased ST in V1-6, 1 and aVL
reciprocal ST depression in 2,3 and aVF
standing different in resting potential
