Quality Issues and Artefact

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.

Electrical interference

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.

Wandering Baseline

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!

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ECG Library (165)

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In the ECGquest archives, this ECG has been tagged with: - 12-Lead Incorrect Machine Interpretation Anterior ST elevation Hyperacute T waves Acute Anterior MI Dr Smith's ECG Blog CC BY-NC
Acute Chest pain in a 50-something, and a “Normal” ECG

This ECG is from a man in his 50s who presented with acute chest pain.

This ECG shows anterior ST elevation with hyperacute T waves. The cause was a 100% proximal LAD occlusion.

In the ECGquest archives, this ECG has been tagged with: - 12-Lead Electrical interference artefact Dr Smith's ECG Blog CC BY-NC
What are all these little spikes?

This ECG is from an elderly woman who presented after a fall.

This ECG shows frequent artefact spikes due to a bladder stimulator implanted for her neurogenic bladder.

In the ECGquest archives, this ECG has been tagged with: - 12-Lead Nonspecific baseline artefact Dr Smith's ECG Blog CC BY-NC
A Text Message in the Middle of the night. Do you give thrombolytics? Repeat ECG

This ECG is from a man in his 60s who presented with chest pain.

This ECG shows baseline artefact obscuring most features of the ECG.

In the ECGquest archives, this ECG has been tagged with: - 12-Lead Incorrect Machine Interpretation Delta wave Wide QRS Wolff Parkinson White syndrome Dr Smith's ECG Blog CC BY-NC
What do you think about this Left Bundle Branch Block?

This ECG is from a man with recurrent episodes of tachycardia.

This ECG shows short PR interval with delta waves due to Wolff Parkinson White syndrome.

In the ECGquest archives, this ECG has been tagged with: - Chest pain 12-Lead Incorrect Machine Interpretation Inferior ST elevation Reciprocal ST depression Acute Inferior MI Dr Smith's ECG Blog CC BY-NC
Chest pain resolved, and a “Normal” ED ECG

This ECG is from a middle aged male who presented with chest pain. He was pain free at the time of this initial ECG.

This ECG shows subtle inferior ST elevation with reciprocal change in aVL. The cause was a large inferior infarct.

In the ECGquest archives, this ECG has been tagged with: - 12-Lead Nonspecific baseline artefact Atrial fibrillation Ventricular pacemaker Dr Smith's ECG Blog CC BY-NC
Computer often fails to diagnose atrial fibrillation in ventricular paced rhythm, and that can be catastrophic

This ECG is from an elderly patient who presented with a massive hemiplegic ischemic stroke due to MCA thrombus.

This ECG shows atrial fibrillation with ventricular pacemaker and significant artefact. The AF went undiagnosed.

In the ECGquest archives, this ECG has been tagged with: - 12-Lead Electrode misplacement Lead misplacement ECG of the Week CC-BY-NC-SA
ECG of the Week – 11th February 2019 – Interpretation

This ECG is from a woman in her 70s who presented after an episode of chest pain.

This ECG shows flat lead II and reversal of III and aVF due to complex lead reversals. These changes resolved with correct lead position.

In the ECGquest archives, this ECG has been tagged with: - 12-Lead Incorrect Machine Interpretation Inverted P waves Narrow QRS Retrograde P waves Short PR Accelerated junctional rhythm Dr Smith's ECG Blog CC BY-NC
What is going on here?? (The computer called it “STEMI” and “Intraventricular Conduction Delay”!!)
In the ECGquest archives, this ECG has been tagged with: - Hypotension 12-Lead Nonspecific baseline artefact Bradycardia Extra P waves Irregular Peaked T waves Wide QRS Second degree AV block Hyperkalemia Dr Smith's ECG Blog CC BY-NC
What will you do for this altered and bradycardic patient?

This ECG is from a woman in her 60s who presented from a nursing home with altered mental status, hypotension, hypoxia and bradycardia.

This ECG shows an irregular rhythm due to second degree AV block with wide QRS and peaked T waves. The cause was hyperkalemia.

In the ECGquest archives, this ECG has been tagged with: - Chronic kidney disease 12-Lead Incorrect Machine Interpretation Flat ST segment Peaked T waves Hyperkalemia Dr Smith's ECG Blog CC BY-NC
I saw this computer “normal” ECG in a stack of ECGs I was reading

This ECG is from a woman of unknown age who presented with a clotted dialysis shunt.

This ECG shows peaked T waves and flattened ST segments caused by hyperkalemia.

In the ECGquest archives, this ECG has been tagged with: - 12-Lead Incorrect Machine Interpretation Inferior ST elevation Reciprocal ST depression Acute Inferior MI Dr Smith's ECG Blog CC BY-NC
The computer calls this a “normal ECG”. We’ll just keep making this point.

This ECG is from a middle aged woman who presented with chest pain and dyspnoea that improved after nitrogylcerin.

This ECG shows subtle ST elevation in inferior leads with reciprocal changes in aVL. Troponins were positive. The computer misinterpreted the ECG as normal.

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