This is because each lead is recording the heart’s electrical activity from a different direction (a.k.a viewpoint). Inferior view (calculated by analysing activity between RA+LA -> LL)Įach lead’s ECG recording is slightly different in shape. Lateral view (calculated by analysing activity between RA+LL -> LA) Lateral view (calculated by analysing activity between LA+LL -> RA) Inferior view (calculated by analysing activity between the LA and LL electrodes) Inferior view (calculated by analysing activity between the RA and LL electrodes) Lateral view (calculated by analysing activity between the RA and LA electrodes) Medial or lateral malleolus of the right legĪn ECG lead is a graphical representation of the heart’s electrical activity calculated by analysing data from several ECG electrodes. Medial or lateral malleolus of the left leg The limb electrodes and their placement Electrode Left mid-axillary line at the same horizontal level as V4 and V5Ĭhest electrode positions Limb electrodes Left anterior axillary line at the same horizontal level as V4 ElectrodeĤth intercostal space at the right sternal edgeĤth intercostal space at the left sternal edgeĥth intercostal space in the midclavicular line The chest electrodes and their placement. The electrodes used to generate a 12-lead ECG are described below. lead I is calculated using data from the electrodes on both the right and left arm). The data gathered from these electrodes allows the 12 leads of the ECG to be calculated (e.g. ElectrodesĪn ECG electrode is a conductive pad attached to the skin to record electrical activity. Only 10 physical electrodes are attached to the patient to generate the 12 leads. An ECG lead is a graphical representation of the heart’s electrical activity which is calculated by analysing data from several ECG electrodes.Ī 12-lead ECG records 12 leads, producing 12 separate graphs on a piece of ECG paper.An ECG electrode is a conductive pad attached to the skin to record electrical activity.Understanding the difference between an ECG electrode and an ECG lead is important: Each large square represents 0.2 seconds.Each small square represents 0.04 seconds.The paper used to record ECGs is standardised across most hospitals and has the following characteristics: The components of an ECG How to read ECG paper It represents the time taken for the ventricles to depolarise and then repolarise. The QT interval begins at the start of the QRS complex and finishes at the end of the T wave. It represents the time between two QRS complexes. The RR interval begins at the peak of one R wave and ends at the peak of the next R wave. It appears as a small wave after the QRS complex. The T wave represents ventricular repolarisation. The ST segment is an isoelectric line representing the time between depolarisation and repolarisation of the ventricles (i.e. The ST segment starts at the end of the S wave and ends at the beginning of the T wave. It appears as three closely related waves on the ECG (the Q, R and S wave). The QRS complex represents the depolarisation of the ventricles. It represents the time for electrical activity to move between the atria and the ventricles. The PR interval begins at the star t of the P wave and ends at the beginning of the Q wave. In healthy individuals, there should be a P wave preceding each QRS complex. You may also be interested in our ECG interpretation OSCE stations available as part of our collection of 800+ ready-made OSCE stations.
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