Getting the electrodes well positioned is critical for recording a good quality ECG. Here are some common problems that you might encounter when you are recording a 12-lead ECG.
The Evil Bunny Ears: V1/2 Too High
It is very common to place the first two chest electrodes too high. If this has happened, the QRS complex may have developed ‘evil bunny ears’ that can be easily mistaken for an incomplete right bundle branch block. The T waves in these leads may also become inverted and mimic a heart attack. This will all go back to normal if the ECG is repeated with the V1 and V2 electrodes in the 4th intercostal space.
Shave That Hairy Chest: Poor Skin Contact
If the patient is sweaty, hairy or moving around, the electrodes may not be in good contact with the skin. If you see artefact like this, check the electrodes are in good contact with the skin. This is even more likely if only some of the leads are affected as some electrodes may be in better contact than others.
The Mirror Image: Switched Arm Leads
Some electrode swaps are hard to pick, but if you notice that Lead I has become a complete upside-down mirror image of normal then check the left and right arm electrodes. This pattern can be caused by accidentally putting the left arm electrode (LA) on the right arm, and vice versa. If in doubt, repeat the ECG and double check that RA is on the right arm and LA on the left arm.
If the baseline looks like it has become a thick marker pen, it may be due to interference from electrical devices. Nerve stimulators can also create a similar artefact with lots of spikes close together. If possible, eliminate the source of the artefact, or adjust the filters on your ECG machine.
Oops, he flatlined: Electrodes falling off
If you see a flatline on the ECG it is more likely to be an electrode falling off (or a faulty wire) than a cardiac arrest – especially if only some leads are affected. If in doubt, check the patient!
Electrodes on Limbs vs Torso: Does it Matter?
Traditionally the limb electrodes are placed on the arms and legs. There is some evidence that placing these electrodes more proximally (i.e. on the trunk) can affect the ECG and can even obscure some signs of infarction. However, it might also reduce artefact from limb tremors. Consider marking the electrode placement the ECG if you do use a non-standard position.
A wandering baseline can be a frustrating occurrence that makes interpreting the ST segments very difficult. Try to get the patient to relax (stop moving around), breathe calmly (if possible) and check the electrodes are in good contact with the skin. Sweaty patients are a challenge!