An electrocardiogram, popularly known as an ECG, is a recording of the
heart's electrical activity. The test may be carried out by your doctor or a
hospital to see if there is any disorder in your heart rhythm.
The heart is a muscular bag which pumps blood by contracting and relaxing.
Messages for the muscle to contract (shorten) are carried electrically from
one part of the heart to another and it is this electrical current which is
recorded on a machine called an electrocardiograph.
The reading it gives - a wavy ink line on a roll of paper - is called an
electrocardiogram (popularly known as an ECG) and is extremely useful in
diagnosing heart complaints. The process is totally painless and has no
REASONS FOR AN ECG
If you visit your doctor with severe chest pains, it is quite likely that
you will have an ECG. The doctor may be equipped to carry this out in his
surgery or you may have to visit your local hospital, An ECG is used to help
diagnose a wide variety of heart troubles, such as a hole in the heart or a
heart attack, or disorder of heart rhythm (arrhythmia).
Sometimes insurance companies require a person to have an ECG if they want
further information after an initial check-up. Airline pilots often have one
as part of their yearly medical examination.
HOW IT IS DONE
Early ECG recordings were made by putting both arms and a leg in buckets of
salty water (brine is a good conductor of electricity) along with a wire
from a galvanometer (which measures changes in electrical currents).
Modern electrocardiographs use less chilly procedures. They consist of a
more sophisticated galvanometer. The patient lies on a couch and electrodes
are attached by rubber bracelets to each wrist and ankle or clipped on to
sticky patches attached to the skin. A movable electrode is stuck on the
chest with a suction cup so that readings can be taken from various points.
Inside the galvanometer there is a voltage-sensitive needle with paper
passing beneath it. Each time the heart beats, the flow of electricity makes
the needle move and the heartbeats are traced on the paper as humps and
THE HEART'S STRUCTURE
The heart has four chambers, two upper smaller ones known as the left and
right atria (auricles) and the larger lower chambers, the left and right
ventricles. The atria are receiving chambers and the ventricles are pumping
For the heart to beat away at a regular rate of around 70 beats per minute,
with a faster beat if exercising, it has to have a sophisticated timing
system. The timing for the ventricles - the two main pumping chambers -
comes from a tiny natural 'pacemaker' in the atria, the thin-walled chambers
that collect blood from the lungs and the rest of the body.
Each cardiac cycle starts with the two atria contracting; then, after a
small pause, the ventricles contract together. Then they relax and begin a
new cycle. This process shows up as a small hump called the P wave, which
represents the atria contracting, followed by spikes which are the
ventricles contracting. These spikes are known as the QRS points.
Most of the electrical activity the ECG picks up comes from the major
thick-walled pumping chamber, the left ventricle, because this contains most
of the heart muscle. The major spikes on the recording come from the voltage
change as the powerful left ventricle contracts.
The ventricles then relax and recharge, shown in the ECG above as the T
wave, before the cycle starts all over again.