Table 4.2 Interpretation of an ECG

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1. Assess the quality of ECG. Check the calibration of the amplitude of deflection, the paper speed and whether the filter was on or off. Look for artefacts.
2. Calculate the heart rate. Establish whether it is fast, slow or normal, and whether it is variable.
3. Assess the overall rhythm. Establish whether changes in rhythm are intermittent or persistent and whether they are induced or terminated by excitement or any procedures such as a vagal manoeuvre (e.g. ocular pressure or carotid sinus massage).
4. Assess each wave/complex in turn. Measure the duration and amplitude of the P wave and QRS complex and the duration of the intervals. Establish whether all the complexes are similar or not.
5. Examine the relationship between the complexes. Check whether each P wave is followed by a QRS complex, and whether there is a P wave before each QRS complex.
6. Define the heart rhythm and a plan for further diagnostic investigations and treatment if necessary.