ECG warning signs of impending TdeP VT other than prolongation of the QT interval include T-wave and U-wave fusion (sometimes with giant TU waves) Post-extrasystolic changes in repolarization pattern Macroscopic T-wave alternans (visible alternation of two different appearing T-waves) Frequent polymorphic ventricular premature beats representing single beats of TdeP (often in bigeminy) Repetitive short runs of polymorphic ventricular tachycardia The TdeP VT itself is a rapid, polymorphic VT that tends to self-terminate.