Tryndamere died in ult [GAMEPLAY]

In a match linked above i playd as Tryndamere against the Zyra and all other team. I play'd with Tryndamere more then 800 games total on different accounts, so I guess I know his ult timing and all other things. So I was hella frightened, when fighting Zyra in my jungle I died 0.5s after turning on my ult, I heard his rage shout ending while was dead. BTW it was first time i try new keystone (with vampiric) maybe here's the key?