Technical Problems: Difference between revisions
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* '''Arm - foot switches''' lead to a very small or 'far field' signal in leads II or III. | * '''Arm - foot switches''' lead to a very small or 'far field' signal in leads II or III. | ||
* '''Chest lead reversal''' lead to inappropiate R wave progression (increase - decrease - increase) and are often easily recognized. | * '''Chest lead reversal''' lead to inappropiate R wave progression (increase - decrease - increase) and are often easily recognized. | ||
Therefore '''any right axis or small signal in an extremity lead''' should be reason enough to check lead positioning. A previous ECG can be very helpful. | |||
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Revision as of 07:55, 15 October 2009
| Author(s) | J.S.S.G. de Jong | |
| Moderator | J.S.S.G. de Jong | |
| Supervisor | ||
| some notes about authorship | ||
Lead reversals
Lead switches are a common mistake when ECGs are made and can lead to wrong diagnoses. Common mistakes are:
- Left - right arm reversals. This leads to a negative complex in lead I with also a negative P wave in lead I. It is one of the most common causes of right axis deviation on the ECG!
- Arm - foot switches lead to a very small or 'far field' signal in leads II or III.
- Chest lead reversal lead to inappropiate R wave progression (increase - decrease - increase) and are often easily recognized.
Therefore any right axis or small signal in an extremity lead should be reason enough to check lead positioning. A previous ECG can be very helpful.
Right and left arm lead reversal can be distinguished from the (much rarer) dextrocardia by looking at the precordial R wave progression.
Right arm and left leg lead reversal. Lead II now measures the signal between the left and right leg, which is remote from the heart.
A patient with dextrocardia (and previous inferior myocardial infarction)
More specific patterns with every lead reversal:
- right leg and right arm:
- Hardly any signal in lead II.
- right and left arm electrodes;
- reversal of leads II and III
- reversal of leads aVR and aVL
- left arm and left leg:
- reversal of leads I and II
- reversal of leads aVR and aVF
- inversion of lead III
- right arm and left leg:
- inversion of leads I, II and III
- reversal of leads aVR and aVF
It is possible to distinguish lead reversal and dextrocardia by watching the precordial leads. Dextrocardia will not show any R wave progression in leads V1-V6, whereas lead reversal will.
Artifacts
Movement artifacts
Increasing movement artifacts in a Parkinson patient. The patient was in sinus rhythm! (which doesn't show on this short recording)
Baseline drift. The amplifier in the ECG machine has to re-find the 'mean'. This often occurs right after lead connection and after electric cardioversion.
Cardioversion from atrial fibrillation to sinus rhythm, with clear baseline drift.
Electrical interference from a nearby electrical appliance. A typical example is a 100 Hz background distortion from fluorescent lights. Not to be confused with atrial fibrillation.
Another example of an artefact caused by an electrical appliance. The patients rhythm is regular. This strip shows 10 QRS complexes.
An artifact that was originally diagnosed as a VT
Artifacts (disturbances) can have many causes. Common causes are:
Movement
Electrical interference