You were incredibly unlucky with your 1st heroic, both Ahn'kahet dungeons have some tricky details that you rarely worry about as dps but can become paramount as the tank. In Old Kingdom heroic, for example, the Ahn'kahar Spell Flinger casts a spell that reduces your health to 20% per cast; whether your max health is 60k or 24k, it is potential wipe inducer.
Part of great tanking is learning, and preparing, in advance potential perils. As you continue tanking, you'll pick up on these details and hopefully carry on into Cataclysm with greater confidence.
And oh yes... welcome to the tanking corps