Understanding the ECG Part 2: ECG basics

In this second article, we take a more detailed look at the 12-lead ECG. Our aim is to familiarise you with the layout of the 12-lead ECG, and to help you to understand the relationship between ECG leads and the different areas of the heart. We also consider common factors that affect the accuracy of recording, and offer the reader a method of interpretation that we believe facilitates systematic analysis of the ECG. Finally, we describe the first step in this system of interpretation: the assessment of heart rate, rhythm and intervals. Leads I remember once being approached by a junior member of staff in the Emergency Department who informed me that the ECG machine was broken. ‘There are only 10 leads,’ she told me, ‘instead of the 12 that there should be’. After a simple explanation of what lead means in ECG terms, she realised that she had a fully functioning piece of equipment.

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