ECG

Definition
Electrocardiography :is a process of recording electrical activities of heart muscle at skin surface.
Electrocardiograph : is machine amplify and record the electrical activity on a moving strip of paper.
Electrocardiogram: is the record from this procedure.

P Wave
?represents atrial depolarization
?first upward deflection
?usually 0.10 seconds or less.
PR segment
?is isoelectrical.
? between end of P wave and beginning of QRS wave.
?It is due to delay in conduction of cardiac impulse through AV node (0.12 – 0.2 s).
Interval
PR OR PQ
?time impulse takes to move through atria and AV node
?between the beginning of P wave and beginning of Q or R wave because Q wave is frequently absent.
?normally QRS Complex
?represents ventricular depolarization
?usually < 0.12 sec.
Q wave: first negative deflection after P wave.
odepolarization of septum
R wave: first positive deflection after P wave.
?Depolarization of LV
S wave:
?negative deflection
?Depolarization oST Segment
?early repolarization of ventricles.
?is from end of S wave to beginning of T wave. It is coincides with the plateau of ventricular action potential.
?elevation or depression may indicate abnormality Of RV.

QT interval
?which is measured from the onset of QRS complex to end of the T wave(0. 35-0.45s), represents the ventricular depolarization and repolarization.