New Ground for Ancient Artifacts

Dear Readers,

Anyone who has reviewed a cardiac rhythm strip is well aware that electrocardiographic artifact can mimic an arrhythmia. The literature is full of case reports, common sources, and various categorizations of artifact. However, new technologies that are capable of generating a recording of the electrical activity of the heart are continually being developed. Therefore, it is important to include this old problem of artifact in one’s differential diagnosis when interpreting tracings generated by even these new and improved technologies.

Why is it so important to recognize a case of artifact? It is critical that artifact not be misinterpreted as an arrhythmia, because of the profound implications that an incorrect diagnosis of a heart rhythm problem can have for a patient. A report in 1999 described 12 patients with artifact who, after being misdiagnosed as having ventricular tachycardia (VT), were treated unnecessarily with cardiac medications including amiodarone and lidocaine, transferred to another hospital or to an intensive care unit, subjected to invasive procedures including invasive electrophysiology testing and cardiac catheterization, and underwent device implantation including pacemakers and defibrillators.¹ In a subsequent survey of physicians, a rhythm strip that showed an artifact mimicking monomorphic nonsustained VT was misinterpreted as VT by 82% of internists, 57% of cardiologists, and 36% of electrophysiologists.²

Electrocardiographic artifact can simulate a variety of arrhythmias including monomorphic VT, polymorphic VT, atrial flutter, and bradycardia. Clues that a recording that appears to be a wide complex tachycardia actually represents artifact include:

• Patient or electrode movement during the recording.
• QRS complexes, or portions of the QRS complexes and sometimes T-waves, visible at expected intervals within the artifact.
• Unstable recording baseline before or after the episode.
• Presence of a QRS complex at a time that would not be physiologic, such as immediately after a QRS complex when the ventricles would be expected to be refractory.
• Absence of expected QT prolongation on the first recorded beat after an apparent long pause.

Artifact can also mimic non-arrhythmic cardiac abnormalities including acute myocardial infarction³ and pseudo-pacemaker stimuli.⁴

An example of a relatively new cardiac recording technology that is not immune to artifact is the implantable loop recorder. This device is highly effective in the evaluation of patients with recurrent unexplained syncope, and is able to determine the burden of atrial fibrillation in patients over a prolonged period of monitoring. However, it is important to recognize that although the technology is new, it is still vulnerable to the same pitfalls of conventional surface recordings. An example of apparent asystole that was retrieved from an implantable loop recorder on the day after implantation is shown below:

Note that there is an apparent absence of signal suspicious for a long pause and that the device “detects” asystole. However, also note the abrupt upstroke and decay in the baseline immediately before the flat line, and the abrupt downstroke and decay immediately before sinus rhythm is recorded. This is consistent with loss of electrode contact, not sinus arrest. Even though an implantable loop recorder is totally subcutaneous, the electrode can come out of contact with the subcutaneous tissue when there is a small amount of air in the pocket. It is not uncommon for a small amount of air to be present in the pocket after placement of any cardiac rhythm device shortly after implantation. Failure to recognize that this recorded episode is artifact could easily lead to unnecessary implantation of a pacemaker.

Sometimes it is important to periodically hit the refresh button and remind ourselves of well-known problems such as electrocardiographic artifact when evaluating patients with lesser known newer devices that record and display the cardiac rhythm. If artifact is not considered, it will not be diagnosed.

References

1. Knight BP, Pelosi F, Michaud GF, et al. Clinical consequences of electrocardiographic artifact mimicking ventricular tachycardia. N Engl J Med 1999;341:1270–1274.
2. Knight BP, Pelosi F, Michaud GF, et al. Physician interpretation of electrocardiographic artifact that mimics ventricular tachycardia. Am J Med 2001;110:335–338.
3. Hall BW, Knight BP. An abnormal electrocardiogram in a young man: What is the etiology? Pacing Clin Electrophysiol 2002;25:1510–1512.
4. Smelly MP, Childers R, Knight BP. Pseudo-pacemaker stimuli. Pacing and Cardiac Electrophysiol 2008;31:513–516.