[GAMEPLAY] Tryndamere Ult Activating but not actually working

While in a game (late game), an enemy Warwick ulted on me while an Ashe was also autoing me. Now of course, I'm frantically smashing my 'r' button in hopes that when I am released from his ult, I can make an attempted escape/revenge, but no. Unfortunately, I died. I accepted the fact that maybe, I didn't have enough health. Now up until this point you're probably wondering "Where's the problem, dude?" Well here is the problem. If I can't ult while he is ulting me and I drop to zero, then I'm dead. But, if I am out of his ult, and I ult, I should have at least 5 more seconds to live, right? Not the case. In the flurry of my spamming 'r' and his and Ashe's wailing on me, I died. But what confused me is that I heard the sound of Tryn ulting and my ult went on cooldown, which means that I was alive and out of his ult long enough to ult, but I was still dead. So if anyone could please explain this to me. Maybe he has a millisecond from activation to casting time, and they killed me then or something like that? Idk. Anyways, thanks!