to determine the value of alternation of qrs morphology in determining the site of origin of sustained narrow qrs supraventricular tachycardia ( svt ) , we retrospectively studied 163 distinct tachycardias in 161 patients ( ages 4 to 91 years ) in whom the site of origin of svt was proven by intracardiac electrophysiologic study .
C0039231
tachycardias
C0039240
svt