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Info bulb.pngMany pages or sub-pages on conditions make some mention of ECGs, these actually link here

An electrocardiogram (ECG or in the US commonly EKG) is a recording of the electrical activity of the heart with respect to time. The ECG can be recorded on paper or presented visually on a screen.

Usually the recording is made at the body surface (surface ECG). More rarely an electrocardiogram can be measured at the heart surface by direct contact with electrodes and in some electrophysiological studies via an oesophageal probe.

The best way to learn how to interpret an Electrocardiogram is to look at a lot and keep looking at a lot more, correlating the findings on the ECG with the history and findings from the patient. Follow a regular and logical pattern of analysis. There are books and websites which can help [1] but they are no substitute to experience in pattern recognition. If you need revision to acute physician level try Dr Smith's ECG blog as it brings multiple internet resources together. Many modern machines will produce an electronic report. Such reports are not infallible and you know enough when you start picking up a machines mistakes for something like QTc interval when other rare pathology causes a wave form issue.

Invention of a workable electrocardiograph is credited to Willem Einthoven[2][3]


Normal ECG

  • How a 12-lead ECG is performed
  • How to interpret an ECG
  • Normal intervals
  • Normal variants


  • Adopt a methodical approach to analysing ECG to avoid missing things
  • Treat the patient, not ECG.
  • Conversely, a normal ECG does not exclude pathology
LogoKeyPointsBox.pngA normal ECG does not exclude serious pathology including a current MI

Conduction Abnormalities

Left bundle branch block
Right bundle branch block


Reverse ticking seen in patient on digoxin

Ischaemic Heart Disease

Lateral ischaemia

Ischaemic heart disease can cause several different types of ECG abnormalities. That this was the case was first demonstrated in experiments in dogs published in 1918. Previous infarcts can give rise to Q-waves, which signify previous full-thickness infarction. Other non-specific findings include T-wave inversion and conduction abnormalities.

In the setting of acute chest pain, an ECG is performed immediately to look for evidence of myocardial infarction or ischaemia. This is of particular importance as thrombolysis is indicated if certain criteria are met.

Hypertensive heart disease

Left ventricular hypertrophy

The ECG in chest disease

Metabolic and others

Congenital heart disease


Resources for learning about ECG