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Additionally, when recording an ECG, the left leg lead (which is the positive electrode for leads aVF, II and III) is always coloured Green by convention (Europe, not USA). Therefore Green is the colour for all three inferior leads (II, III, aVF). The left arm ECG lead (which is the positive electrode for aVL and lead I) is always Yellow. Hence the four lateral leads (I, aVL, V5, V6) are Yellow. Similarly the right arm ECG lead (positive electrode for aVR) is always Red, so the right-ward leads (aVR, V1) are Red. The remaining fourth primary colour, Blue, is used for the anterior Leads V2-4; especially important as this is prognostically the most significant territory for an MI. Consequently, Blue is viewed beforeRed: . ECG paper could even be printed colour-coded for clarity and understanding (Fig. 1).
Colour-coding the chest leads themselves would promote correct placement: to the right of the sternum (4th inter-costal space), running from the left of the sternum, with being more lateral (Fig. 1).
The groupings correlate broadly to the blood supply of the heart walls, hence the logic of understanding the basic anatomy of the coronary arterial supply (Fig. 1). This correlation is explained on page 26, Chapter 4, of the ALS Manual.
Which myocardial territory is involved typically determines which groupings of leads/colours are affected:
± septum: , extending to .
It is easier to detect differences by comparing and contrasting four coloured groupings – as opposed to 12 individual ECG leads, especially for ST segment changes associated with acute coronary syndrome – typically raised in infarction and depressed in ischaemia, the opposite being the case for posterior changes. Ischaemia is a frequent cause of cardiac arrest and arrhythmia requiring timely recognition. ‘Reciprocal Changes’ can develop in other leads from those demonstrating infarction, which is of help in substantiating infarction. The possible need for additional chest leads to the right of for detection of Right Ventricular Infarction, and to the left of for detection of Posterior Infarction must be remembered.
It is useful for such logical understanding to keep basic coronary anatomy in mind. The right coronary artery (RCA) and circumflex artery (horizontal division of the left coronary artery), both run in the atrio-ventricular groove, the former anteriorly, the latter posteriorly. The left anterior descending artery (LAD) (the vertical division of the left coronary artery) and the posterior descending artery (PDA) both run in the inter-ventricular groove, the former anteriorly and the latter posteriorly (Fig. 1).
As with history taking and clinical examination, pattern recognition – here of the 12-Lead ECG – is paramount. By systematically and sequentially comparing and contrasting four distinct ECG groupings – as opposed to 12 individual leads – colour by colour, we suggest detection of abnormalities is simpler. Colour-coding of the chest leads , , would also help secure correct placement.
Conflict of interest statement
No conflicts of interest to declare.
We thank Anne Wodmore and Chris Priest, Medical Illustration Unit, Imperial College Healthcare Trust, for Figure.
Advanced life support (ALS).
6th ed. Resuscitation Council UK, Tavistock House North, Tavistock Square,
London WC1H 9HR2011