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(Circulation. 2000;101:2870.)
© 2000 American Heart Association, Inc.

Images in Cardiovascular Medicine

"Switched" Precordial Leads

J. Willis Hurst, MD

From the Department of Medicine, Emory University School of Medicine, Atlanta, Ga.

Correspondence to J. Willis Hurst, MD, 1462 Clifton Rd, NE, Suite 301, Atlanta, GA 30322. E-mail jhurst{at}emory.edu

Most physicians and technicians have, at one time or another, inadvertently "switched" the extremity leads in preparation for the recording of an ECG. This is so common that some modern ECG machines advise the operator that he or she has switched the leads.

Misplacement of the electrode positions is the most common error related to recording the chest leads. The next most common cause of error is probably switching the V₁ and V₂ electrode positions on the chest. This error is easy to make because the wires attached to the lead selector box are adjacent to each other.

During our cardiology morning report, I was shown several ECGs. Two of them were quite unusual. I could not construct the spatial direction of the mean QRS vectors; the frontal plan calculation was easily diagrammed, but the anterior-posterior direction could not be constructed. One of these tracings is shown in Figure 1. There was a tall R wave in lead V₁, a small R wave in lead V₃, and tall R waves in leads V₄ through V₆. The resultantly negative QRS complex at position V₃ was out of place. It appeared that the QRS complex in lead V₃ was more likely recorded from the V₁ position and the QRS complex in lead V₁ was recorded from the V₃ position. If this was true, how did it happen?

View larger version (110K): [in this window] [in a new window]   Figure 1. ECG showing switched chest leads V1 and V3.

I inspected the ECG machine that was used by the new night technician. Inspection of the lead selection box yielded the explanation. The lead wire that was labeled at its end as V₁ was plugged into the V₃ receptacle of the lead selector box and the lead wire labeled V₃ was plugged into the V₁ receptacle of the lead selector box. The new night technician had undoubtedly looked only at the labeling at the end of wires. The corrected ECG is shown in Figure 2.

View larger version (111K): [in this window] [in a new window]   Figure 2. ECG showing corrected chest leads.

How could this happen? The wire that connects the lead selector box to the electrode placed on the chest may occasionally break near the clamp used to attach the wire to the electrode. When this happens, the wire must be replaced. In this case, it appears that 2 wires were replaced. The individual who made the replacement plugged lead V₁ into the V₃ position on the box and plugged V₃ into the V₁ position on the box (see Figure 3).

View larger version (31K): [in this window] [in a new window]   Figure 3. Source of error. Note that lead V1 is attached to position V3 on the lead selector box and that lead V3 is attached to position V1 on the box.

There are other abnormalities in the tracing. They are not discussed here because the purpose of this communication is to point out what must be an uncommon type of "switched" chest leads. The computer, of course, failed to recognize the error.

Footnotes

The editor of Images in Cardiovascular Medicine is Hugh A. McAllister, Jr, MD, Chief, Department of Pathology, St Luke’s Episcopal Hospital and Texas Heart Institute, and Clinical Professor of Pathology, University of Texas Medical School and Baylor College of Medicine.

Circulation encourages readers to submit cardiovascular images to the Circulation Editorial Office, St Luke’s Episcopal Hospital/Texas Heart Institute, 6720 Bertner Ave, MC1-267, Houston, TX 77030.

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