Run the first 200m as your slowest.
Staying still before the gun, your heartrate drops, no matter how much jumping about you did just before you were told to toe the line. Then the gun goes off, and your heart rate jumps up again as you sprint off to a 69 second 400. You pay the price for that on the second lap (apparently), and by the third you are running more efficiently.
Slow down.
Let your heart work for you--don't work against it: you need it more than anything else you've got. Let it start to pump faster gradually--it will be ready by the time you need it around laps three and four.
Going out in 74/75 is what you want, but, honestly, going out in 72 would be a strong improvement. If you run out of juice on your first two laps, you're toast. The goal should be to float through the first half of your race as effortlessly as possible, taking no more than 51% of your total expected time to cover that distance (and no less than 49% of your total time--this part is your problem). Then you need to attack the third quarter to avoid slowing down. Unless you run yourself into a hole, you will always have something for the last lap.
Calm down and keep breathing.