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ECG

The Anesthesia Guide » Topics » ECG

Author:
Kai Knudsen



Updated:
17 May, 2025

With ECG, one monitors pulse, heart rhythm, conduction abnormalities and ischemic events. ECG can also reflect changes in electrolyte balance with changes in potassium, magnesium, and calcium. ECG is standard monitoring during anesthesia and intensive care and provides a reliable measure of heart function. ECG can be momentary, continuous as during anesthesia, or "collected" over a longer period, known as "Holter ECG." Disturbances in the ECG are common during anesthesia, but it remains a basic safety measure in monitoring. ECG is typically interpreted using 3, 5, or 12 leads. During anesthesia, 3-lead ECG is standard, but if ST changes also need to be interpreted, a 5-lead ECG is used. Below are instructional images of ECG.

Content:
  1. Electrocardiogram
  2. Electrolyte abnormalities reflected in ECG
  3. Regional circulatory detektion by ECG

Electrocardiogram

The ECG shows the electrophysiological process of the heartbeat. The different waves in the heartbeat are labeled P, Q, R, S, and T.

  • P wave: This shows atrial depolarization, meaning the electrical activity that triggers the contraction of the atria (the upper chambers of the heart).
  • QRS complex: This represents ventricular depolarization, which triggers the contraction of the ventricles (the lower chambers).
    • The Q wave is the initial downward deflection.
    • The R wave is the next upward deflection.
    • The S wave is the following downward deflection.
  • T wave: This indicates ventricular repolarization, the process of the ventricles recovering electrically in preparation for the next contraction.

Each of these waves gives important information about the heart’s rhythm and function.

Electrolyte abnormalities reflected in ECG

Regional circulatory detektion by ECG

 

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