Basic Principles

DEFINITION:

Electrocardiogram is a record of electrical activity of the heart by placing the electrical leads on the surface of the body.

This is done on a graphic paper consisting of small(1 mm) and large squares(5 mm).These squares help to measure the timing and deflexion amplitudes of the EKG tracing.The time is measured on horizontal axis and voltages(amplitude) on the vertical axis.

For a quick reading and convenience of the human eye,the EKG is universally recorded at a paper speed of 25mm/sec.At this speed,the marker moves one large square in 0.2sec and five large squares in 1 second on the EKG paper.On the vertical axis each small square represents 1mV and each large square 5mV.So,to check whether the voltage is adjusted properly or not,we need to look at the voltage standard which is placed at the beginning of the recording.Usually it is maintained at a voltage of 10mV.In obese or in individuals with thick chest wall,we may need to increase the voltage for proper assessment of the EKG.Here are some basics to remember:

One small square : 0.04sec and 1mV
One large square : 0.2sec and 5mV
Five large squares: 1 sec

EKG Recording:

The electrical leads are positioned on the body by placing the electrode gel on the skin to reduce the electrical resistance at the electrode-skin interface.The patient is advised to be calm and breathe gently to avoid the skeletal muscle interference.Its good to know the reasons for certain abnormalities in the ECGs.They could be:

1) Wandering Baseline: movement,twisted cables,poor electrode contact and poor insulation.
2) Skeletal muscle interference

EKG Interpretation:

If we read an EKG in a systematic way,then the chances of missing any important finding is minimal.The following are considered in its evaluation:

Rate
Rhythm
P-R Interval
QRS complex
T wave
Q-T Interval
U wave

Each one is explained individually in its respective section.