Pseudoalternans

Report:

Sinus tachycardia 111/min

VEBs in bigeminy

Fusion beats

Comment:

The first fusion beat appears at the end of the top strip. The middle strips show VEBs in bigeminy, without fusion; the bottom strip shows later-coupled VEBs in fusion, mimicking alternans.

The PR intervals in the bottom strip are identical and the trace would be indistinguishable from true electrical alternans if one did not know of the preceding bigeminy. True alternans cannot be ruled out completely, but remains quite unlikely. All medical diagnoses depend on their context.

VEBs can actually cause a transient alternans, but did not do so here (top strip, when bigeminy stops). The VEBs participating in fusion are probably not the same ones seen during obvious bigeminy - there is a major increase in the coupling interval that permits fusion to occur.

Below is a strip from a 49 year old woman gasping for breath in cardiogenic shock, for some reason on a mirror-image V1 lead. She has a movement artefact helpfully placed in front of all the larger complexes. Tachypnœa is another cause of pseudoalternans. She also suffers from chronotropic incompetence.