How would you go about getting and ECG in England?

You would have to go through your GP or health visitor. It is possible to do these on a child of this age but it isn't easy because the patient needs to sit very sit while the reading is being taken. It is only for a few seconds but show a child of this age that will sit still at all, without the stress of having stickers all over and being in a clinical environment. I wouldn't worry about this. If your husband has a history they would keep an eye on any symptoms that show, and if there isn't any then all is well.