Propranolol induced electrical and mechanical alternans in orthodromic reciprocating tachycardia

During an electrophysiological study in a patient with a concealed accessory connection, there was no evidence of electrical or mechanical alternans during tachycardia until propranolol was administered, but both forms of alternans developed with tachycardia of a slower rate following propranolol. Echocardiographic, arterial pressure, and electrocardiographic data obtained prior to and following propranolol administration are presented.