What is an ECG Wave?

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  • Written By: Jacqueline Byrne
  • Edited By: A. Joseph
  • Last Modified Date: 09 November 2019
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An electrocardiogram (ECG) wave, sometimes called an elektrokardiogramm (EKG) wave, is a diagnostic tool used by clinicians to analyze the electrical activity of the heart in order to determine heart health. The heart contracts to propel blood through the body and contraction is achieved through a series of electrical impulses that are generated by the heart. It is this electrical activity over time that is detected by an electrocardiogram and is recorded onto a graph as an ECG wave. Electrocardiograms are commonly seen in clinical and emergency room settings and are usually equipped with an alarm system that serves to alert the hospital staff of abnormal heart behavior.

The human heart consists of two atria and two ventricles that make up four chambers. The heart functions by pumping blood from the outside of the body into the atria, through the ventricles and back into the body. During rest, the muscles of the heart chambers are polarized, meaning that they have an electrical charge.

In order to generate the energy to contract, these muscles must "spend" their electrical charge and depolarize. The chambers must then recharge in preparation for the next contraction, and this is referred to as repolarization. Depolarization and repolarization describe changes in electric potential that is detected by electrodes placed on the skin and represented by the ECG wave.


The ECG wave can be broken down into the P wave, the QRS complex and the T wave, and those waves — which are named arbitrarily after an alphabetical sequence of letters — repeat in that order for every heartbeat. The P wave occurs because of atrial depolarization, which initiates a wave of contraction to squeeze blood into the ventricles. To pump blood back into the body, ventricular depolarization occurs. Atrial repolarization and ventricular depolarization happen almost simultaneously and are represented on an ECG wave by the QRS complex.

After the blood has been ejected from the ventricles, the ventricles then repolarize. This repolarization is represented by the T wave. Both the P wave and T wave have positive — or upward — displacements on the graph, even though one wave represents a loss of charge and the other represents a gain in charge.

From an ECG wave, clinicians can learn abundance of information about the health of the heart. It can be used to determine the muscle mass of the heart, whether the heart is beating properly, whether there is proper blood flow through the heart and even the effects of a drug or drugs on the heart. Clinicians analyze the P wave, QRS complex and T wave for their magnitude, order of occurrence, frequency and shape in order to gather this information.


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