The key, per published reports, is where you acquired your Watch. If you bought it in the US, you will be able to use the ECG app now. If not, you can’t.
No amount of playing with regions, either in your phone or your iTunes account will change this. This is very locked down, and for a good reason: if Apple allowed such easy methods of gaining access to this in countries where it has not been approved, Apple could face fines, lawsuits and could even be barred from selling the Watch or even the iPhone.
Don’t be angry at Apple about this: it’s just following the law. Ask your governments to fast track approval if you want this soon.