Electrocardiography

Electrocardiography (ECG or EKG)

is an interpretation of the electrical activity of the heart over time captured and externally recorded by skin electrodes. It is a noninvasive recording produced by an electrocardiographic device.

The ECG works by detecting and amplifying the tiny electrical changes on the skin that are caused when the heart muscle is activated during each heart beat. At rest, each heart muscle cell has a charge across its outer wall. During each heartbeat a healthy heart will have an orderly progression of an electrical wave that is triggered by the cells in the sinoatrial node, activates the atria, runs though “intrinsic conduction pathways” and then spreads all over the main chambers. This is detected 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.

A 12-lead ECG is one in which 12 different electrical signals are recorded at approximately the same time and is used as a one-off recording of an ECG.

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 heart attack, the ECG can identify if the heart muscle has been damaged in specific areas, though not all areas of the heart are covered. The ECG cannot reliably measure the pumping ability of the heart, for which ultrasound-based (echocardiography) or nuclear medicine tests are used.