Electrical Alternans - What Is It? QRS of Varying Size

Author: V. Dimov, M.D.
Reviewer: A. Aneja, M.D.

A 78-year-old African American male (AAM) with a past medical history (PMH) of diabetes type 2 (DM2), chronic renal insufficiency (CRI), and hypertension (HTN) is admitted to the hospital with a chief complaint (CC) of confusion for several hours. The blood glucose was 40 mg/dL.

He was given one ampule of D50 by the EMS and was admitted for a D10W IV drip and evaluation.


Lasix (furosemide), glyburide, rosiglitazone (Avandia), aspirin (ASA), famotidine (Pepcid).

Physical examination

VS 36.5-80-14-153/83.
Chest, CVS, abdomen: WNL.
Neuro: AAO x 3, nonfocal.

Laboratory results

At baseline, BUN 25 mg/dL, Cr 2.3 mg/dL.

Final diagnosis

Hypoglycemia due to the combination of oral DM medications and CRI (low creatinine clearance).

What happened?

The patient had no further symptoms, his blood glucose was stable, his PO meds were adjusted (glyburide was stopped), and he was discharged (D/C'd) home within 24 hours.

Why are we presenting this case?

During his hospital stay, the nurse noted some changes on the monitor - the QRS complex was changing its size. See the telemetry strip (click to enlarge the image).

Electrical alternans (click to enlarge the image).

This ECG phenomenon is called electrical alternans and can be caused by the variety of conditions.

The classic example is a pericardial effusion with the heart "swinging" in it and changing its location and proximity to the chest wall (where the electrodes are) from beat to beat. See the 2D Echo video from Texas Heart Institute.

Our patient did not have any serious condition and was discharged home.


Cardiac Tamponade and Electrical Alternans. Texas Heart Institute, video.
Electrical Alternans. eMedicine.
Electrical Alternans. NEJM Images.
Pericardial effusion with electrical alternans. ECG Library.
Swinging of the heart and electrical alternans due to a large pericardial effusion. NEJM, 10/2009.

Published: 04/12/2006
Updated: 09/29/2010


  1. The upper tracing shows a cyclical variation in the QRS amplitude every 4 cycles. This is respiratory variation in the QRS amiplitude and is a common observation in intensive care units. If could be either due to changes in thoracic impedance with the respiratory cycle or due to the change in the distance of the heart from the recording electrodes. The 4:1 ratio also suggests that it is a respiratory cycle, being the usual pulse to respiration ratio.

  2. Well,We do see this sort of activity in a few patients as they come off bypass.
    Tends to resolve quite quickly.There we do not see any impact of the respiratory excursions.
    Also I agree with Francis

  3. The term "Electrical Alternans" should be used only when there is an ECG abnormality (amplitude or morphology) affecting every other beat, i.e., one beat to the next beat. It is not so in this case. Therefore,title and the caption for ECG image are incorrect.

    1. get a life and a clinical practice!

    2. That "get a life" is a little harsh, especially because 1) you don't know who the person is, and 2) you are wrong. According to Wellens HJJ, "QRS alternans during narrow QRS tachycardia has been demonstrated to have a high degree of specificity for orthodromic circus movement tachycardia [sometimes called AV reentry} and is therefore helpful in differentiating this type of tachycardia from other types of tachycardia."
      NOTE: CMT is the AV reentry type seen in WPW syndrome. The circuit is anterograde in the Nodal-His axis and retrograde in the accessory pathway, thus the narrow QRS.
      In QRS alternans the pattern is EXACTLY as pointed out by the first "Anonymous".