During the last few years, the number and types of instruments used for noninvasive and invasive (electrical and nonelectrical) study of cardiac functions have multiplied. Naturally, physicians and hospital administrators have concentrated their attention on them. Technicians have been more interested in working in these more lucrative services. Such factors, and others, have downgraded the importance of recording 12-lead ECGs, relegating them to less qualified personnel. Not surprisingly, the quality of technicians and of the ECG that they record has deteriorated in many centers. Optimal quality can only be achieved if the parties involved understand what is happening. The following are some of the artifacts commonly seen in current routine 12-lead ECGs. They are important because they can confound the interpreter and, worse, the computer program.

Muscle Tremor and Alternating-Current Interference

These are the most frequently encountered artifacts because some patients will continue to have disease processes producing tremor and because the amount of electronic equipment causing interference in a hospital environment has increased.

Improper Limb-Lead Positioning

This has become more frequent after relaxation of quality control, especially in hospitals with inadequate standards for hiring technicians and with poor on-site training. Mixing up the cables from the ECG machine has gone beyond switching the right arm and left arm cables.!! Various types of misplacements of only one cable are illustrated in Fig. 11-38. The method depicted in this illustration, based on the use of unipolar extremity leads only, is simpler than those incorporating the analysis of bipolar standard leads.!! Not frequently recognized in ECG textbooks is the incontrovertible fact that in some centers even the "sanctity" of the attachment of the right leg (ground) cable to the right leg has been violated136 (Fig. 11-39). In our experience, this error is usually identified as improper lead placement, but determination of the cables involved is usually not made correctly.136

Coble connection to electrodes

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