An electrocardiogram (ECG or EKG) is one of the simplest and fastest
procedures used to evaluate the heart. An EKG records the electrical
activity of the heart, shows abnormal rhythms (arrhythmias or
dysrhythmias), and detects heart muscle damage. An EKG may be
conducted in several ways and used in combination with other tests,
such as a stress or exercise test, to evaluate heart function and rhythms.
Your physician uses the EKG to determine the heart rhythm and
information about the heart’s electrical signals.
Electrodes (small, plastic patches) are placed at certain locations
on the chest, arms, and legs. When the electrodes are connected to an
EKG machine by lead wires, the electrical activity of the heart is
measured, interpreted, and printed out for the physician's information
and further interpretation.
How an EKG works
The EKG records the electrical signals as they move through the
heart. In normal rhythm the electrical signals starts at the heart’s
own pacemaker, called the sinus node. The electrical signal first
spreads through the heart’s upper chambers called the atria. The
electrical signal spreading through the atria produce a noticeable
bump or deflection called the "P wave."
Next, the normal signals travel from the heart's top chambers, the
atria (plural of atrium), to the lower chambers by traveling through a
connector or staircase called the A-V node. The time the electrical
impulse takes to travel through the A-V node make up the major part of
the period of time to go from the atrium to the ventricle and is
measured as the "P-R interval." In some conditions, this
time may be increased. In some situations, some of the signals do not
make it from the atrium to ventricle, a condition called A-V block or
Next the impulse travels to the lower heart chambers, the
ventricles. On the EKG, this produces a signal called the QRS complex.
The time that the electrical signals take to reach all parts of the
ventricles determines the width of the QRS complex. In some cases, an
extremely wide QRS complex can result in a decreased efficiency of the
heart’s electrical system.
One the ventricles have been activated, the ventricles start to get
ready to be activated again. This process called repolarization
produces a deflection called the T wave. The time period from the
beginning of the QRS complex to the end of the T wave is known as the
QT interval. The QT interval may be prolonged due to a variety of
conditions including the effect of medications, heart muscle
abnormalities, heart attack, or genetic conditions that may lead to
serious lower chamber fast rhythms called ventricular
Other related procedures that may be used to assess the heart include: