what does a single ECG complex comprise of?
individual waves and lines that occur in a specific sequence as a result of depolarization and repolarization
isoeletric line
the baseline of an ECG tracing
waveform
deflection or movement away from the baseline
segment
the line between 2 waveforms
interval
consists of a waveform and a segment
complex
a collection of waveforms ie) QRS complex
what are the components of an ECG?
P wave, PR interval, QRS complex, ST segment, T wave, QT interval
in lead II, which electrode is positive and which is negative?
LL is positive
RA is negative
what does the P wave represent?
atrial depolarization
if the P wave is normal, what would the direction of electrical flow be?
from R to L and down toward positive electrode
P Wave
- location
- amplitude
- duration
- configuration
- deflection
- precedes QRS complex
- 2-3mm high
- 0.06-0.12 seconds
- rounded and upright
- positive and upright in lead II
what does the isoelectric line represent?
after atria are depolarized, wave of depolarization continues towards AV node and junctional tissues and there’s a short pause in electrical flow allowing atria to recover and repolarize
isoelectric line location?
immediately after P wave
what does the PR interval represent?
amount of time it takes for the electrical impulse to leave the SA node, depolarize the atria, and pass through the AV junction
PR interval
- location
- duration
- composed of
- beginning of P wave to beginning of QRS complex
- 0.12-0.20 seconds
- composed of P wave and PR segment
what does the Q wave represent?
- delay of electrical activity at AV node
- after delay, wave of depolarization flows toward bundle of His then to L bundle branch
- interventricular septum is depolarized from L to R
Q wave
- location
- deflection
- after a P wave and PR interval
- first negative deflection
what does the R wave represent?
wave of depolarization continues down bundle branches and flows over bulk of ventricular tissue
R wave
- location
- deflection
- right after Q wave
- large upright positive deflection because: electrical current is directed down towards positive electrode and b/c ventricles are depolarizing
what does S wave represent? its deflection?
- electrical flow extends up to Purkinje fibers
- flow of electrical current is away from positive electrode = small negative downwards deflection
QRS complex represents?
- location
- duration
- all of ventricular depolarization from endocardium to epicardium
- follows PR interval
- 0.10 seconds or less
- measured to end of S wave
what does the ST segment represent?
early ventricular repolarization
what does the T wave represent?
- atrial repolarization activity is hidden in QRS complex b/c atrial tissue is smaller
- ventricular repolarization is more visible
- ventricular tissue recovers or repolarizes from epicardium to endocardium and electrical flow goes toward (+) electrode
T wave deflection
positive upright
