Electrical alternans is an

electrocardiographic Electrocardiography is the process of producing an electrocardiogram (ECG or EKG), a recording of the heart's electrical activity. It is an electrogram of the heart which is a graph of voltage versus time of the electrical activity of the hear ...

phenomenon of alternation of

QRS complex The QRS complex is the combination of three of the graphical deflections seen on a typical electrocardiogram (ECG or EKG). It is usually the central and most visually obvious part of the tracing. It corresponds to the depolarization of the ri ...

amplitude or

axis An axis (plural ''axes'') is an imaginary line around which an object rotates or is symmetrical. Axis may also refer to: Mathematics * Axis of rotation: see rotation around a fixed axis * Axis (mathematics), a designator for a Cartesian-coordinat ...

between beats and a possible wandering base-line. It is seen in

cardiac tamponade Cardiac tamponade, also known as pericardial tamponade (), is the buildup of fluid in the pericardium (the sac around the heart), resulting in compression of the heart. Onset may be rapid or gradual. Symptoms typically include those of obstructi ...

and severe

pericardial effusion A pericardial effusion is an abnormal accumulation of fluid in the pericardial cavity. The pericardium is a two-part membrane surrounding the heart: the outer fibrous connective membrane and an inner two-layered serous membrane. The two layers of t ...

and is thought to be related to changes in the ventricular electrical axis due to fluid in the

pericardium The pericardium, also called pericardial sac, is a double-walled sac containing the heart and the roots of the great vessels. It has two layers, an outer layer made of strong connective tissue (fibrous pericardium), and an inner layer made o ...

, as the heart essentially wobbles in the fluid filled pericardial sac. The echocardiogram of the heart demonstrated the characteristic swinging along with alternating voltage on the ECG.Electrical Alternans with Pericardial Tamponade
New England Journal of Medicine, 20 August 2015, Generally electrical alternans can be seen with tamponade, and narrow AV junctional reentrant

tachycardia Tachycardia, also called tachyarrhythmia, is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 100 beats per minute is accepted as tachycardia in adults. Heart rates above the resting rate may be normal ( ...

with an accessory pathway (such as WPW syndrome). A similar phenomenon, pseudo-alternans, can be seen in bigeminal (premature ventricular contraction) PVC in the PR interval, alternans pre-excitation, and alternans

bundle branch block A bundle branch block is a defect in one the bundle branches in the electrical conduction system of the heart. Anatomy and physiology The heart's electrical activity begins in the sinoatrial node (the heart's natural pacemaker), which is situat ...

. For the most part however, the most serious condition to rule out is tamponade. Electrical alternans with

sinus tachycardia Sinus tachycardia is an elevated sinus rhythm characterized by an increase in the rate of electrical impulses arising from the sinoatrial node. In adults, sinus tachycardia is defined as a heart rate greater than 100 beats per minute (bpm). The ...

is a highly specific sign for large pericardial effusion. This is due to the swinging motion of the heart in the pericardial cavity causing a beat-to-beat variation in QRS axis and amplitude. Patients with cardiac tamponade and hemodynamic compromise should have emergency pericardiocentesis.

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Cardiac arrhythmia {{circulatory-disease-stub

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