Warning : Use the following information at your own risk. While accuracy is one my goals, there is always the possibility that some of the information could be wrong. There could be typos. I could also be severely mistaken in some of my knowledge. This site is meant to help clarify certain concepts of ECG and at no point should any life-or-death decision be made based upon the information contained within. Remember, this is just some page on the internet. (If you do find errors, please notify me by feedback.)
The word artifact is similar to artificial in the sense that it is often used to indicate something that is not natural (i.e. man-made). In electrocardiography, an ECG artifact is used to indicate something that is not "heart-made." These include (but are not limited to) electrical interference by outside sources, electrical noise from elsewhere in the body, poor contact, and machine malfunction. Artifacts are extremely common, and knowledge of them is necessary to prevent misinterpretation of a heart's rhythm.
These are seen in someone whose implanted pacemaker is firing.
The sharp, thin spike seen in figure x-x is an electrical signal produced by an artificial pacemaker. The wide QRS complex that follows it represents the ventricles depolarizing. We say that the "(artificial) pacemaker captures" when it is able to successfully depolarize its intended target. If a pacing spike is not followed by its intended response, we say that it has failed to capture.
The wide QRS suggests that the pacemaker was implanted in the ventricles.
Reversed leads / misplaced electrodes
Electrode/lead placement is very important. If one were to accidentally confuse the red and white lead cables (i.e. place the white one where the red one should go, vice versa), he might get an ECG that looks like figure 12-2. In this ECG, we can make out a normal sinus rhythm with all of the waves upside-down. When this happens, you are essentially viewing the rhythm in a completely different lead.
One must also make sure that the lead wires are actually plugged into the machine. If your talkative patient shows asystole, you should suspect this. Many machines are "smart" in that they can sense common errors of this nature, but many such errors aren't always readily apparent.
Alternating current (AC) describes the type of electricity that we get from the wall. In the United States, the electricity "changes direction" 60 times per second (i.e. 60 hertz). (Many places in Europe use 50 Hz AC electricity.) When an ECG machine is poorly grounded or not equipped to filter out this interference, you can get a thick looking ECG line (as shown in figure 12-3). If one were to look at this ECG line closely, he would see 60 up-and-down wave pattern in a given second (25 squares).
Muscle tremor / noise
The heart is not the only thing in the body that produces measurable electricity. When your skeletal muscles undergo tremors, the ECG is bombarded with seemingly random activity. The term noise does not refer to sound but rather to electrical interference.
Low amplitude muscle tremor noise can mimic the baseline seen in atrial fibrillation. Muscle tremors are often a lot more subtle than that shown in figure 12-4.
In wandering baseline, the isoelectric line changes position. One possible cause is the cables moving during the reading. Patient movement, dirty lead wires/electrodes, loose electrodes, and a variety of other things can cause this as well.
Absolute heart block
Absolute heart block (or 4th degree heart block) results from over-exposure to imported-liquor advertisements in magazines. QRS complexes are wide and bottle-shaped and show no relationship with the P wave. It occurs very rarely, and even then, only in fictional settings. This should not be confused with the real arrhythmia complete heart block.