Abnormal ECG
I think that Homunculus has already given you a good overview, and I would agree that a 1mm. change in the ST segment is hardly proof of any major problems with your heart, particularly given your age, height, weight and non-smoking history. In giving advice about this, I always try to put myself in the same dilemma and ask myself what I would do. In this case, I would go ahead with the renewal. Your ECG will then be sent to Gatwick where it will be scrutinised by a cardiologist with wide experience of Aviation Cardiology. If he is happy with it, then that's all that will happen. If he has doubts, you will be asked to have an effort ECG, and if there is a problem, then the ST shift will become more marked, and further investigations could be called for. ECG changes are not uncommon, and most of them turn out to be completely benign, so stay cool!