Normal electrocardiogram

Normal electrocardiogram

Objective:
1-Draw an ECG classical waveform and label each component (P wave, QRS complex wave, and T wave).
2-Draw normal ECG of 12 leads standard unipolar (aVR, aVL, aVF) and bipolar limb leads (L 1, L 2, L 3 ) and unipolar chest leads(C 1, …….C 6).
3-State the direction of cardiac vector.
4- Normal cardiac vector.
5- How draw cardiac vector from bipolar limb leads.
6-How find HR from regular ECG and irregular ECG.
The electrocardiogram:
Because the body fluid is good conductors, algebraic sum of the action potentials of myocardial fibers can be recorded externally. The record of this potential fluctuation during cardiac cycle is called electrocardiogram (ECG). Most electrocardiograph machines record these fluctuations on moving strip of paper. The names of these waves and segments are:
1- P wave represents atrial depolarization. Atrial repolarization is buried in QRS complex, because it is too slow and diffuse to register. It is about 0.07 – 0.14 seconds and not more than 3 mm.
2- PR segment is due to the delay in conduction through AV node. It is isoelectric because insulating fibrosis prevents the electrical circuit and no current flow.
3-PR interval is measured from the beginning of the P wave to the beginning of the QRS complex. This interval corresponds to the time taken for the impulse to travel from the sinus node to the ventric¬ular muscle. It ranges normally between 0.12- 0.21 seconds.
4- QRS complex represents depolarization of the ventricles. The duration is about 0.06 – 0.10 seconds. Abnormal wide QRS indicate bundle branch block.
5- ST segment is the segment from end of the S wave to the beginning of the T wave. It is isoelectric, which coincides with the plateau of ventricular action potential.
6- T wave represents ventricular repolarization. It is positive because repolarization occurs in reverse sequence to depolarization, producing the upright T wave. The duration is about 0.25 -0.35 seconds and not taller than 10 mm in chest leads.
7- QT interval represents the total time from the onset of ventricular depolarization to the completion of repolarization. It indicates the duration of