Last updated on April 24, 2014 at 16:01 EDT


Electrocardiography, sometimes called ECG or EKG, is a measurement of the electrical activity of the heart as the linear process unfolds. With the use of electrodes that are attached to the skin, this non-invasive test can provide vast information as to the patient’s status. By leaving the electrodes attached, the patient’s status can be monitored over intervals of time and recorded on the device. This data can be sent electronically for consults about potential treatments without delay. It is an important tool for cardiac health and treatment.

What the ECG Measures

The ECG follows the electrical activity as it travels through the heart. It measures the rate at which it travels, the pattern in which it repeats, any delays or interruptions in the electricity, and the effect on the patient when the changes appear. This view is only an indirect measurement of the heart’s electrical activity and does not allow the clinician to actually “see” inside the heart. It is more or less considered a voltmeter and it records the activity on graph paper that is then interpreted by a clinician.

Types of ECGs

There are two levels of ECG, a four-lead and a twelve-lead. The level of ECG needed depends on whether the patient’s rhythm needs to be monitored or if the patient’s rhythm needs to be interpreted.

The Four-Lead ECG

The four-lead ECG is typically used to monitor a patient or to get a quick glimpse at what rhythm the patient’s heart is in currently. The four electrodes have a specific placement on the patient in order to view the electricity that is moving across the heart. It does not matter what order the electrodes are placed, only that they are all placed. The electrodes are placed on the left arm, the left leg, the right arm and the right leg. If the patient is unable to remain still, the electrodes can be placed on the torso nearest to the proper extremity. Once placed, the rhythm should display on the monitor for the technician to see.

The Twelve-Lead ECG

The first difference between the two types of ECG is the number of electrodes used in the procedure. The four-lead also provides a continual view of the rhythm while the twelve-lead only provides a 2.5 second view of the rhythm. That is considered enough time to view a representative complex from each section of the heart.

The additional leads are sought to expand the view of the ECG for the clinician to interpret. While it is called a twelve lead, “lead” is a reference to the view that is created by the electrodes placed on the body. There are only ten electrodes placed on the patient for the twelve-lead ECG. The additional electrodes are placed on the patient’s torso and use the existing four-lead electrodes to create additional views. The first electrode, V1, is placed on the space between the fourth and fifth right-sided ribs about an inch from the center of the chest. The second electrode, V2, is placed in the same spot on the left-side of the chest. Next V4 is placed in order to provide the correct spacing. It is placed between the fifth and sixth rib in line with the left nipple. Then V3 is placed between V2 and V4. V5 will be placed next to V4 vertically in-line with the front of the left arm. And finally V6 is placed next to V5 vertically in-line with the center of the armpit. After several ECGs, the technician can place the electrodes quickly by remembering key anatomical locations.

The names of the leads on the twelve-lead ECG are I, II, III, AVF, AVL, V1, V2, V3, V4, V5 and V6. They combine to see different areas of the heart. II, III and AVF allow the clinician to view the inferior side. V1 and V2 represent the septal area of the heart. V3 and V4 comprise the anterior area while V5, V6, I, and AVL combine to show the lateral area of the heart. This is particularly important when the tracing indicates that cells are presently being damaged. The indication, commonly referred to as heart attack, is not only identified as occurring but also pinpointed as to where in the heart it is occurring.


The use of an ECG is very common place in the medical world. It can be utilized as part of an examination, diagnosis, monitoring, treatment and post procedural evaluation. The patient it is used on could be symptomatic or asymptomatic. For example, if a patient presents to their doctor with chest pain or shortness of breath then an ECG would be completed to help with a diagnosis. Also if a patient presents to their doctor for a well-check at the age of forty then they too would receive an ECG based on their age. It is also used during surgeries to monitor patient status or to see the improvement after a cardiac procedure has been performed. ECGs have numerous uses and are utilized daily.

ECGs are like fingerprints in the fact that they are unique for each patient. There are patterns in the rhythm that may be alike between patients but each is different in its entirety. It is because of this that thorough interpretation of each part of the tracing must be scrutinized.

Image Caption: Diagram showing the connection of ECG leads. Credit: Madhero88/Wikipedia