EKG / ECG

Electrocardiography (ECG or EKG)

What is an EKG, or what is an ECG?

Electrocardiography (ECG or EKG from the German Elektrokardiogramm) is a transthoracic (across the thorax or chest) interpretation of the electrical activity of the heart over a period of time, as detected by electrodes attached to the outer surface of the skin and recorded by a device external to the body. The recording produced by this noninvasive procedure is termed an electrocardiogram (also ECG or EKG). The device is commonly referred to as an ECG or EKG machine.

The etymology of the word is derived from the Greek electro, because it is related to electrical activity, cardio, Greek for heart, and graph, a Greek root meaning "to write". In English speaking countries, medical professionals often write EKG (the abbreviation for the German word elektrokardiogramm) in order to avoid confusion with EEG in emergency situations where background noise is high.

Electrocardiogram machines, or ECG and EKG machines, have become some of the most common equipment used to record and measure normal or abnormal action within the heart. The use of EKG machines has become so common due to the wide variety of heart disorders that an ECG machine will detect, along with the ease and speed in which the test is accomplished. Some of the disorders which can be detected by the ECG machine include: valve disease, electrolyte disturbances, prior heart attacks, coronary artery disease, thickening of the heart muscle, and a broad range other possible cardiac problems. Most EKG machines are 12-lead interpretive EKG machines.

Most ECGs are performed for diagnostic or research purposes on human hearts, but may also be performed on other animals, usually for research.

Function

The ECG machine detects and amplifies the tiny electrical changes on the skin that are caused when the heart muscle depolarizes during each heartbeat. At rest, each heart muscle cell has a charge across its outer wall, or cell membrane. Reducing this charge towards zero is called depolarization, which activates the mechanisms in the cell that cause it to contract. During each heartbeat a healthy heart will have an orderly progression of a wave of depolarisation that is triggered by the cells in the sinoatrial node, spreads out through the atrium, passes through "intrinsic conduction pathways" and then spreads all over the ventricles. This is detected by the EKG machine as tiny rises and falls in the voltage between two electrodes placed either side of the heart which is displayed as a wavy line either on a screen or on paper. This display indicates the overall rhythm of the heart and weaknesses in different parts of the heart muscle.

Usually more than 2 electrodes are used and they can be combined into a number of pairs (For example: Left arm (LA), right arm (RA) and left leg (LL) electrodes form the three pairs LA+RA, LA+LL, and RA+LL). The output from each pair is known as a lead. Each lead is said to look at the heart from a different angle. Different types of ECGs can be referred to by the number of leads that are recorded, for example 3-lead, 5-lead or 12-lead ECGs (sometimes simply "a 12-lead"). A 12-lead ECG machine is one in which 12 different electrical signals are recorded at approximately the same time and will often be used as a one-off recording of an ECG, traditionally printed out as a paper copy. 3- and 5-lead ECGs tend to be monitored continuously and viewed only on the screen of an appropriate monitoring device, for example during an operation or whilst being transported in an ambulance. There may or may not be any permanent record of a 3- or 5-lead ECG machine, depending on the equipment used.

It is the best way to measure and diagnose abnormal rhythms of the heart, particularly abnormal rhythms caused by damage to the conductive tissue that carries electrical signals, or abnormal rhythms caused by electrolyte imbalances. In a myocardial infarction (MI), the ECG machine can identify if the heart muscle has been damaged in specific areas, though not all areas of the heart are covered. The ECG machine cannot reliably measure the pumping ability of the heart, for which ultrasound-based (echocardiography) or nuclear medicine tests are used. It is possible for a human or other animal to be in cardiac arrest but still have a normal ECG signal (a condition known as pulseless electrical activity).

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