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10 top tips - ECG recording

Practical advice from Dr Kathryn Griffith, secretary of the Primary Care Cardiovascular Society

Practical advice from Dr Kathryn Griffith, secretary of the Primary Care Cardiovascular Society

Make sure the ECG machine is always charged up and ready to use and ensure you always have spare electrodes. Patients who have palpitations in the surgery can't always wait to come back to have an ECG. By then the rhythm may be back to normal and a valuable chance to make a diagnosis will be lost. Make sure the team members who are recording ECGs are trained in the correct techniques to produce quality recordings. Chest hair should be removed and chest leads placed in relation to intercostal spaces and not pendulous breasts!

Always try to have a standardised technique for reporting ECG. Don't get distracted at the start by something you are not sure about. Often abnormalities fall into place during the reporting process.

Look at the rhythm strip at the bottom first. What is the heart rate? Divide the number of large squares between the qrs complexes into 300.

Then logically analyse the p wave, the pr interval and the qrs complex. What is the rhythm? Is there evidence of atrial depolarisation? Is the rhythm regular? What is the relationship between atrial (p wave), and ventricular depolarisation (qrs complex)?

When there are more p waves than qrs complexes this indicates block at the AV nodal level. This is commonly seen with atrial flutter where there are regular atrial waves at 300 beats per minute and block at the AV node giving 2:1 block and a regular ventricular rate of 150 or 3:1 block and a rate of 100 beats per minute.

Work along the trace to the pr interval. Is the timing between the start of the atrial depolarisation (p wave) and the ventricular depolarisation (qrs complex) normal? A very short time might suggest an ectopic focus such as a nodal rhythm, and a long time might be related to AV nodal block.

The next step is to look at the axis. You now can move to the other leads on the recording. This usually refers to the axis of ventricular depolarisation in the limb leads. Remember that lead 1 is at 0 degrees and aVF at 90 degrees. A normal axis lies between lead aVL (-30 degrees) and 90 degrees. The easy approach is to look at leads 1 and aVF and if the ventricular complexes are positive then the axis is normal.

Are the qrs complexes normal width? Look at the chest leads. Is there evidence of bundle branch block? Remember that right bundle branch block may be a normal variant while left bundle branch block should make you suspect underlying pathology.

Look at the T waves, which should be the same polarity as the qrs complex. Inverted T waves are common in lead III and aVL when the axis is zero and do not necessarily indicate a myocardial infarct.

Remember that the ECG is only part of the assessment of the patient. If a patient is fit and well and the ECG report suggests ventricular fibrillation, check the leads first and make sure there is no electrical interference in the room.

The integrated computers in modern ECG machines tend to over-diagnose abnormalities. Always try to report the ECG yourself first without looking at the report and if necessary have one GP in the practice who is confident at looking over all the ECGs done in the practice. The more you look at the better you will get.

You might be able to get some back-up from a local GPSI in cardiology or a cardiac physiologist or cardiologist at the local hospital. Some specialists are unhappy to look at an ECG alone without being able to assess the patient.

Dr Kathryn Griffith is a GP in York and secretary of the Primary Care Cardiovascular Society
Competing interests None declared


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