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The Electrocardiogram or ECG is a recording of the small electric waves being generated during heart activity.


The Electrocardiogram or ECG is a recording of the small electric waves being generated during heart activity. It is a common procedure performed in the doctor’s office to help determine if the heart’s conductive system is working properly.

The heart

Most people know that the heart is the pump the pushes blood through the body to carry nutrients and oxygen where it is needed, but people are not always conscious of the fact that the “pump” depends on an electrical system to set the heart rate and stimulate the pump.

The heart is made up of four main cavities–the right and left atriums are the top two chambers of the heart and the right and left ventricles are the bottom chambers of the heart.

In a normal heart, the left and right sides of the heart beat together to maintain a steady supply of blood and oxygen to the rest of the body.

A typical heart beat begins with the sinoatrial node, a cluster of specialized cells located in your right upper chamber, firing an electrical impulse that spreads through the walls of the right and left chambers, causing them to contract, thus forcing blood into the lower chambers.

The impulse then travels to the atrioventricular node, another center of special cells located in the lower part of the right atrium. After a short pause, the signal travels into the lower chambers, causing them to contract, forcing blood out of the heart to the lungs and body.

Why the test is performed

An ECG is very useful in determining whether a person has heart disease. If a person has chest pain or palpitations, an ECG is helpful in determining if the heart is beating normally. If a person is on medications that may affect the heart or if the patient is on a pacemaker, an ECG can readily determine the immediate effects of changes in activity or medication levels.

An electrocardiogram is used for a variety of purposes, including:

  • Determine whether the heart is performing normally or suffering from abnormalities (eg. extra or skipped heartbeats – cardiac arrhythmia).
  • May indicate acute or previous damage to heart muscle (heart attack) or ischemia of heart muscle (angina).
  • Can be used for detecting potassium, calcium, magnesium and other electrolyte disturbances.
  • Allows the detection of conduction abnormalities (heart blocks and bundle branch blocks).
  • As a screening tool for ischemic heart disease during an exercise tolerance test.
  • Can provide information on the physical condition of the heart (eg: left ventricular hypertrophy, mitral stenosis).
  • Can suggest non-cardiac disease (e.g. pulmonary embolism, hypothermia)


Taking measurements

An electrocardiogram is a simple and painless procedure.

Sensitive electrodes are placed on chest, upper arms and legs and are connected to an Electrocardiograph, which will record the electric waves emanating from the heart in millivolts. Each electrode controls an ink needle that writes on a grid paper. The higher the intensity of the electric wave, the higher up the needle will move on the paper. The paper moves at a certain speed beneath the needle, resulting in an ink line.

ECG is used to measure the rate and regularity of heartbeats as well as the size and position of the chambers, the presence of any damage to the heart, and the effects of drugs or devices used to regulate the heart (such as a pacemaker).

Peaks and valleys

The ECG curve reflects the perspective of the electrode recording it.

An ECG curve has different characteristics depending on the location of the electrode recording it. When the curve falls below the base line it shows a negative deflection and when it rises above the base line it is a result of positive deflection. A negative deflection indicates that the recorded wave has traveled away from the electrode and a positive deflection means it has traveled towards it.

If the electric or muscular function of the heart is disturbed for some reason, it will affect how the electric signals spread through the heart muscle. Specially trained medical professionals can read these lines and determine normal and abnormal electrical behaviors in the heart.

You are asked to lie down, and electrodes are affixed to each arm and leg and to your chest. This requires cleaning the site and, if necessary, shaving or clipping hair.

You must remain still during the procedure, and you may be asked to hold your breath for short periods. Sometimes this test is performed while you are exercising or under minimal stress to monitor changes in the heart. This type of ECG is often called a stress test.

The results are recorded on graph paper.

Before the ECG, tell your health care provider if you are taking any medications. There are no restrictions for food or fluids. However, ingestion of cold water immediately before an ECG may produce changes in one of the waveforms recorded. Exercise (such as climbing stairs) immediately before an ECG may significantly increase your heart rate.

You may be asked to remove all jewelry and to wear a hospital gown.

The doctor will generally give you the results immediately following the procedure.