Electrocardiography

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12-lead ECG

Electrocardiography (ECG or EKG) is a non-invasive diagnostic procedure that records the electrical activity of the heart over a period of time. The procedure involves placing electrodes on the patient's chest, arms, and legs to measure the electrical impulses generated by the heart. These impulses are then translated into a visual representation called an electrocardiogram, which can help diagnose various heart conditions and abnormalities.

History[edit | edit source]

The development of electrocardiography can be traced back to the late 19th and early 20th centuries. In 1903, Dutch physiologist Willem Einthoven invented the first practical electrocardiograph, for which he received the Nobel Prize in Physiology or Medicine in 1924. Einthoven's invention allowed for more accurate and detailed recordings of the heart's electrical activity, revolutionizing the diagnosis and understanding of various heart conditions.

Principles of Electrocardiography[edit | edit source]

ECG chest lead placement for woman

An ECG works by detecting and amplifying the small electrical changes on the skin that are generated by the heart muscle's electrophysiologic pattern of depolarizing and repolarizing during each heartbeat. Electrodes, usually 10 in number, are placed on the patient's chest, arms, and legs. These electrodes are connected to the ECG machine, which records the electrical activity of the heart and displays it as a series of waves on a screen or printout.

Each wave on an ECG represents a specific part of the cardiac cycle, such as the depolarization of the atria or the repolarization of the ventricles. By analyzing the shape, size, and duration of these waves, physicians can diagnose various heart conditions and abnormalities, such as arrhythmias, myocardial infarctions, and electrolyte imbalances.

Standard 12-Lead ECG[edit | edit source]

The standard ECG procedure uses 12 leads, which provide different views of the heart's electrical activity. These leads are divided into two groups:

  • Limb leads (I, II, III, aVR, aVL, and aVF): These leads record the electrical activity in the frontal plane, which is the plane that runs from the patient's head to their feet. Limb leads are obtained by placing electrodes on the patient's arms and legs.
  • Precordial leads (V1, V2, V3, V4, V5, and V6): These leads record the electrical activity in the horizontal plane, which is the plane that runs parallel to the patient's chest. Precordial leads are obtained by placing electrodes at specific locations on the chest.

Interpreting an ECG[edit | edit source]

An ECG tracing consists of several waves and intervals, each representing a specific part of the cardiac cycle:

  • P wave: The first wave in the ECG tracing, representing the depolarization of the atria.
  • QRS complex: A group of three waves (Q, R, and S) that represent the depolarization of the ventricles.
  • T wave: The final wave in the ECG tracing, representing the repolarization of the ventricles.
  • PR interval: The time from the beginning of the P wave to the beginning of the QRS complex, representing the time it takes for the electrical impulse to travel from the sinoatrial (SA) node to the ventricles.

QT interval: The time from the beginning of the QRS complex to the end of the T wave, representing the duration of ventricular depolarization and repolarization.

By examining the different waves and intervals on an ECG tracing, physicians can assess the heart's rate, rhythm, and electrical conduction, as well as identify any abnormalities that may indicate underlying heart conditions.

Common ECG Abnormalities[edit | edit source]

ST_elevation_myocardial_infarction_ECG

Some common ECG abnormalities include:

  • Arrhythmias: Irregular heart rhythms, such as atrial fibrillation, ventricular tachycardia, or bradycardia, can be detected through abnormal ECG tracings.
  • Myocardial infarctions (heart attacks): An ECG can help identify myocardial infarctions by showing abnormal Q waves, ST-segment elevations or depressions, and inverted T waves.
  • Cardiac hypertrophy: Enlargement of the heart's chambers, such as left ventricular hypertrophy or right atrial enlargement, can be detected through changes in the size and duration of specific waves on the ECG tracing.
  • Conduction abnormalities: ECG can reveal problems with the heart's electrical conduction system, such as bundle branch blocks or atrioventricular (AV) blocks.

Limitations of Electrocardiography[edit | edit source]

While electrocardiography is a valuable diagnostic tool, it has some limitations:

  • An ECG only provides a snapshot of the heart's electrical activity during the time the test is performed. Some heart conditions may not be detected if they do not cause abnormalities during the ECG recording.
  • ECGs can sometimes show false positives, where the tracing appears abnormal even in the absence of any heart conditions.
  • ECGs may not provide enough information to diagnose certain heart conditions, necessitating additional tests such as echocardiography or cardiac stress testing.
  • Despite these limitations, electrocardiography remains a crucial tool in the diagnosis and management of a wide range of heart conditions.
Electrocardiography Resources

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