Baseline ECG normal or maybe slightly long QTc
During (symptomatic)<unk>  episodes
Increased HR leads to progressive ventricular ectopy --> isolated PVCs--> bigeminy--> runs of nonsustained vtach--> sustained Vtach/polymorphic ventricular tachycardia
Echocardiography will show normal heart
Increased HR leads to progressive ventricular ectopy --> isolated PVCs--> bigeminy--> runs of nonsustained vtach--> sustained Vtach/polymorphic ventricular tachycardia
Catecholaminergic polymorphic ventricular tachycardia
Seizure
Idiopathic fascicular left ventricular tachycardia
Toxicologic exposure 
Wandering atrial pacemaker
CO poisoning 
Polymorphic ventricular tachycardia
Breath-holding spell