Electrocardiography

Electrocardiography

Electrocardiography (ECG or EKG, from the Dutch term Electrokardiogram) is a noninvasive technique that involves the interpretation of the heart's electrical activity across the chest wall over a period of time. This electrical activity is detected by electrodes placed on the skin's surface and recorded by an external device. The resulting recording, termed an electrocardiogram (also ECG or EKG), provides valuable information about the heart's functioning.

The primary purpose of an ECG is to assess various aspects of cardiac activity, including heart rate, rhythm regularity, chamber size and position, presence of any cardiac damage, and effects of medications or devices used to manage heart function (such as pacemakers).

The term "ECG" is derived from the Greek words electro (related to electricity), kardio (meaning heart), and graph (meaning to write). In English-speaking countries, "EKG" (abbreviation for the German word Elektrokardiogramm) is often used by medical professionals to avoid confusion with "EEG," especially in noisy emergency settings.

While ECGs are predominantly performed on human subjects for diagnostic or research purposes, they can also be conducted on animals, primarily for research studies.

During an ECG, the device detects and amplifies subtle electrical changes on the skin caused by the heart muscle's depolarization during each heartbeat. This depolarization process triggers the heart muscle cells to contract. The resulting electrical activity is recorded as a series of waves on a screen or paper, representing the heart's rhythm and identifying any abnormalities in different regions of the heart muscle.

Multiple electrodes, typically more than two, are used during an ECG, forming pairs that create various leads to view the heart from different angles. The number of leads recorded determines the type of ECG, such as 3-lead, 5-lead, or 12-lead EKGs. A 12-lead EKG records 12 different electrical signals simultaneously and is commonly printed for analysis. In contrast, 3- and 5-lead EKGs are often monitored continuously on a screen, such as during surgery or ambulance transport, without producing a permanent record.

ECGs are essential for diagnosing abnormal heart rhythms, particularly those caused by damage to the heart's conductive tissue or electrolyte imbalances. While EKGs can identify specific areas of myocardial infarction (MI) or heart muscle damage, they cannot measure the heart's pumping ability accurately, requiring other tests like echocardiography or nuclear medicine studies. Additionally, it's worth noting that an individual may exhibit a normal EKG signal despite being in cardiac arrest, a condition known as pulseless electrical activity.