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 eiectrical or mechanical alfernans during tachycardia until propranolol was adminislered, 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.