EDITORIALS

Electrocardiography Artifact: What You Do NotKnow, You Do Not Recognize

William G. Stevenson, MD, William H. Maisel, MD

“Wat je niet kent, herken je niet” (1). (“Whatyou do not know, you do not recog-nize.”) Reminder to students of electro-

cardiography inscribed in the lecture hall of ProfessorHein J.J. Wellens, MD.

Measurement of the heart’s electrical activity by thesurface electrocardiogram (ECG) was a breakthrough inthe evaluation of cardiac arrhythmias. The ECG is criticalto the safety and care of hospitalized patients with heartdisease. Accurate and timely recognition of life-threaten-ing cardiac arrhythmias is required of all physicianswho work in acute care settings. Of equal importance isthe distinction of arrhythmias from artifact due to dis-connected leads, motion, electromagnetic interference,or equipment failure.

The ECG records electrical activity from cardiac depo-larization and repolarization detected by electrodes onthe skin. The resulting electrical potentials are small (sev-eral millivolts, at most) and occur over a frequency rangeof 0.05 to 100 Hz (cycles per second) (2,3). Signals ofsimilar frequency and of similar or larger amplitude gen-erated by noncardiac sources cause ECG artifact. Thesesignals can be classified as nonphysiologic or physiologic(2). Nonphysiologic artifact is usually caused by poorelectrode contact, electromagnetic interference, or defec-tive ECG equipment. Physiologic artifact can be pro-duced by muscle activitity (electromyographic poten-tials) or skin. Because muscle electrical signals are highfrequency and dissimilar from cardiac electrical activity,they can usually be filtered from the ECG. Skin electricalsignals are produced by movement and stretching of theskin and are the primary source of ECG motion artifact.

Because the potential for ECG artifact is widely recog-nized, the results of the survey conducted by Knight andcoworkers (4) published in this issue of the AmericanJournal of Medicine are surprising. Of 766 physicians whoreviewed an ECG rhythm strip of artifact that mimicked awide QRS tachycardia, only 6% of internists, 42% of car-diologists, and 62% of cardiac electrophysiologists recog-

nized the ECG abnormality. These concerning misdiag-noses occurred despite visible sinus rhythm QRS com-plexes that marched independently through the tracingand were clearly dissociated from the artifact.

The clinical implications of such a misdiagnosis areimportant. Electrophysiologic testing is appropriate forpatients with nonsustained ventricular tachycardia anddepressed left ventricular function after myocardial in-farction because implantable defibrillators (ICD) im-prove survival for those patients found to have inducibleventricular tachycardia. Thus a misdiagnosis of nonsus-tained ventricular tachycardia may extend the hospitalstay or lead to unnecessary cardiac testing. In fact, a ret-rospective review of patients referred for arrhythmiamanagement documented these misdiagnoses (5).

The distinction of artifact from fact is not always easy.Artifact may mimic tachycardia, bradyarrhythmia, orpacemaker malfunction. The reliable hallmarks of eitherundisturbed true QRS complexes marching unimpededthrough the tracing or nonphysiologic rapid or “prema-ture” electrical activity may be absent. When simulta-neous recordings of blood pressure or pulmonary arterypressure are available, as is common in intensive careunits, dissociation of systolic pressure waveforms fromthe surface electrocardiogram may provide clues to thediagnosis of artifact. Occasionally artifact cannot be un-equivocally distinguished from an arrhythmia, and fur-ther assessment guided by concern for the patient’s safetyis appropriate.

Although the findings of this study are concerning, theincidence of clinically relevant misdiagnoses is unknownand may be less than implied by the present study. Sur-veys have important limitations and, by nature, invitebias. The response rate was low; only 16% of internistsand fewer than half of the cardiologists and electrophysi-ologists responded. Perhaps the nonrespondents did notanswer because they felt the ECG was obviously artifact.The inability of the respondents to interview the patientto clarify the clinical context may result in an overestima-tion of the incidence of the problem. Finding that an al-leged 19-beat run of rapid heart action was asymptomaticwould hopefully prompt a more careful review of thetracing with attention to the possibility that artifact is thecause. Despite these limitations, the findings are provoc-ative. Even if the rate of misdiagnosis were reduced by

Am J Med. 2001;110:402– 403.From the Cardiovascular Division, Brigham and Women’s Hospital,Boston, Massachusetts.

Requests for reprints should be addressed to William G. Stevenson,MD, Cardiovascular Division, Brigham and Women’s Hospital, 75Francis Street, Boston, Massachusetts 02115.

402 q2001 by Excerpta Medica, Inc. 0002-9343/01/$–see front matterAll rights reserved. PII S0002-9343(00)00637-4

half, the results of this study would be concerning. It isclear that a substantial number of physicians have diffi-culty recognizing ECG artifact.

The reasons for the high rate of misdiagnosis of ECGartifact are unclear. The ECG is a diagnostic test capableof yielding false negative or false positive results, but it isso routine that it is perhaps taken for granted. PerhapsECG artifact is such a common occurrence that it is nowlargely neglected in formal teaching. A review of six majorclinical cardiology and electrocardiography textbooksdiscloses no discussion of the topic. Apparently, manyphysicians have forgotten how closely ECG artifact canmimic an arrhythmia. We agree with the suggestion byKnight and colleagues that artifact should always beconsidered in the differential diagnosis of an ab-normal ECG. Dr. Wellens advises us that “what you donot know, you do not recognize.” Dr. Knight and col-

leagues remind us that “what you do not look for, you willnot recognize.”

REFERENCES1. Bar FWHM. Main stem stenosis. In: Smeets J, Doevendans P, Jo-

sephson M, et al, eds. Professor Hein J. J. Wellens. 33 Years of Cardi-ology and Arrhythmology. Norwell, Mass: Kluwer AcademicPublishers; 2000:495.

2. Smith M. Rx for ECG monitoring artifact. Crit Care Nurse. 1984;4:64 –56.

3. Bailey JJ, Berson AS, Garson A Jr, et al. Recommendations for stan-dardization and specifications in automated electrocardiography:bandwidth and digital signal processing. Circulation. 1990;81:730 –739.

4. Knight BP, Pelosi F, Michaud GF, et al. Physician interpretation ofelectrocardiographic artifact that mimics ventricular tachycardia.Am J Med. 2001:110:335–338.

5. Knight BP, Pelosi F, Michaud GF, et al. Clinical consequences ofelectrocardiographic artifact mimicking ventricular tachycardia.N Engl J Med. 1999;341:1270 –1274.

Electrocardiography Artifact/Stevenson and Maisel

April 1, 2001 THE AMERICAN JOURNAL OF MEDICINEt Volume 110 403