Electrical alternans
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Synonyms and keywords: QRS alternans, alternans
Overview
Electrical alternans is an electrocardiographic phenomenon which describes teh beat to beat alternation in the height (ie.e amplitude), duration or direction of any of the EKG intervals (e.g. P, PR, QRS, R-R, ST, T, U alternans).
Classification
There can be alternans of any of the EKG waveforms or intervals:
P wave alternans
PR interval alternans
QRS complex alternans
R-R interval alternans
ST segment alternans
T wave alternans
U wave alternans
(of QRS complex amplitude or axis between beats.
Pathophysiology
QRS alternans can be observed in cardiac tamponade and is thought to be related to changes in the ventricular electrical axis due to fluid in the pericardium.
Causes
Differentiating Electrical Alternans form other Disorders
The electrical form of alternans should be differentiated from the mechanical form alternans in which case there is alternation of the strength of the pulse as is observed in pulsus alternans. Electrical and mechanical alternans may coexist.
Electrocardiographic Examples