Electrocardiography (ECG)

Electrocardiography (ECG) is a medical test that records the electrical activity of the heart. ECG measures and graphically records the electrical impulses generated with each heartbeat. This test is widely used to diagnose heart diseases, monitor rhythm abnormalities, and assess cardiac health.

The foundations of ECG date back to the late 19th century. In 1872, German physiologist Willem Einthoven developed the first device capable of measuring the heart’s electrical activity. Einthoven used this device to record the electrical signals of heartbeats and invented the ECG in 1903, for which he was awarded the Nobel Prize. The medical use of ECG began to spread widely in the early 20th century.

ECG records the heart’s electrical signals through electrodes placed on the skin. The heart muscle receives an electrical impulse before each contraction. These electrical signals are detected by the ECG machine and displayed as waves changing over time on a graph.

The ECG device detects electrical currents from the heart using electrodes. These electrodes are typically placed on different areas of the body (chest arms and legs). Different types of ECG exist depending on the number of electrodes; the most common is the 12-lead ECG, which provides a view of the heart’s electrical activity from multiple angles.

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The ECG tracing consists of four main waves:

• P wave: Represents atrial contraction.
• QRS complex: Indicates ventricular contraction.
• T wave: Shows ventricular relaxation.
• U wave: Usually less prominent and reflects the final phase of ventricular repolarization.

Each of these waves corresponds to a specific phase of the heart’s electrical activity.

ECG is typically performed while the patient is in a resting position with electrodes placed on the body. During the test the patient must remain still and breathe normally. The ECG procedure is generally painless although mild discomfort may be felt at the sites where the electrodes are attached.

ECG is a vital tool in the diagnosis and monitoring of heart diseases. Some common applications include:

• Rhythm disorders: Arrhythmia refers to irregular heartbeats and is detected by ECG.
• Heart attack (myocardial infarction): ECG identifies areas of the heart muscle with inadequate blood flow.
• Heart failure: ECG can assist in determining whether the heart is functioning effectively.
• Hypertension: High blood pressure can affect the heart’s electrical activity and is detectable by ECG.
• Cardiac enlargement: ECG can reveal structural changes such as thickening or enlargement of the heart muscle.

ECG results are typically interpreted by a cardiologist. A normal ECG shows waves occurring in a specific pattern and interval. However various abnormalities such as changes in wave morphology or altered intervals may indicate heart disease. Interpretation of ECG must be done in conjunction with the patient’s symptoms clinical condition and other test results.

• Arrhythmias: Irregular heartbeats may appear on ECG as abnormal P waves or QRS complexes.
• ST elevation: May indicate a heart attack. Abnormal elevation of the ST segment suggests oxygen deprivation in heart muscle cells.
• QT interval prolongation: This condition can lead to cardiac rhythm disturbances due to certain medications or genetic disorders.
• Sinus bradycardia and tachycardia: Heart rate slower (bradycardia) or faster (tachycardia) than normal.

• Advantages: ECG is a rapid noninvasive and mostly painless test. It requires no special preparation and typically yields results within minutes. ECGs can also be performed using portable devices.
• Limitations: ECG measures only the heart’s electrical activity and does not reveal structural heart disease. Some heart conditions may not be apparent during the ECG and may require additional tests.