ECG basics Flashcards
P wave represents
depolarization of the artria
QRS represents
depolarization of the ventricle (absolute refractory periord)
what cardiac myocyte action potential phases are represented by QRS
phase 0 and phase 1 (absolute refractory period)
Q
first downard deflection following P (not always present)
R
first upeard deflection of QRS complex
S
any negative deflection following and R wave
T wave represents
ventricular repolarization
apex of T wave represents what phase of cardiac myocyte action potential
phase 3 (relative refractory period)
what is a U wave
repolarization of purkinje fibers and papillary muscle - appearance of U wave is indirectly related to heart rate (usuallly seen in low HR - athletes)
J point
1.) first point of inflection of upstroke in S wave 2.) point at which ECG trace becomes more horizontal than verticle
where is PR interval measured
onset of P wave to onset of QRS
what does PR interval represent
time for impulse to travel from SA node to ventricles
what is the normal PR interval in adults? In kids?
Adults: 0.16-0.20 Kiddos: 0.12-0.20
PR segment is measured where
end of P wave to onset of QRS
PR segment represents
duration of contraction through bundle of his, bundle brances and purkinje fibers
RR interval represents
instantaneous heart rate
QT interval measured
onset of Q to end of T
QT represnets
electrical systole - duration of ventricular depolarization and repolarization
what is the normal QT interval
0.25-0.40
ST segement potential measurement
end of S wave to the inset of T wave
ST segment potential represents which phase of cardiac myocyte action potential
phase 2
location of V1 electrode
right of the sternum in the fourth intercostal space
location of V2 electrode
left of the sternum in fouth intercostal space
location of V4
left mid clavicular line in fith intercostal space
location of V6
left midaillary line
location of V3
between V2 and V4
location of V5
between V4 and V6
what is the normal value for QRS complex
0.06-0.10
left axis deviation occur between what angles
0 and -90
Extreme right axis devation occurs between what angles
Between -90 and + or 180
Right axis devation occurs between what angles
Between + (-) 180 and 90
what direction does depolarization occur
Endocardium to epicardium
In what direction does repolarization occur
from epicardium to endocardium
describe the wave progression in the chest leads
R waves get bigger from V1 to V6, S waves get smaller from V1 to V6
how do you do a quick estimate of normal QT interval
normal QT should be less than half of the preceeding RR interval
Mean QRS in hypertrophy
mean QRS toward the hypertrophied side - why? Hypertrophied side will have greater depolarization activity
Mean QRS in infaction
mean QRS AWAY from the infarct. Why? The necrotic tissue does not depolarize
Mean QRS in bundle block
TOWARDS the block
Pathological Q wave
greater than 3 mm or greater than 25% of the R wave
what do you see on ECG in the recovery phase of infarct
ST segment and T wave return to normal but pathological Q wave can persist for months
