True vs. pseudo-electrical ventricular alternans sustained by ventricular premature complexes.

This report describes a form of electrical ventricular alternans sustained by ventricular premature complexes (VPC). Alternans was associated with a constant heart rate (RR interval) and was therefore considered to be either a form of classic or true alternans or a mimic of the configuration seen in true alternans from other causes. In contrast, VPC-induced pseudo-alternans is characterized by an inconstant heart rate (RR interval). It is surprising that the incidence of true VPC-induced alternans is unappreciated and virtually unreported, most probably since the measurement of the RR intervals involving late VPCs is ignored.