Electrical alternans

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Electrical alternans is an electrocardiographic phenomenon of alternation of QRS complex amplitude or axis between beats. Also a wandering baseline may be seen. It is seen in cardiac tamponade and is thought to be related to changes in the ventricular electrical axis due to fluid in the pericardium.

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The majority of factors that cause A-V blocks can result in blockage of the peripheral ventricular Purkinje system. This often result in a block of every other heart beat. The electrical alternans can be attributed to tachycardia as in this condition it is impossible for all the Purkinje fibres to recover from their previous refractory period to conduct the new impulse and as such a few heart beats are lost resulting in electrical alternans pattern which can be illustrated by an ECG. Also many other conditions such as ischemia, myocarditis, and digitalis toxicity can cause incomplete intraventricular block and thus result in electrical alternans.