The ECG feature on Apple Watch Series 4 is now accessible outside of the US. This feature uses electrodes (available on the rear of the smartwatch) to read your heat rate and identify any abnormal patterns. You can present the reading to your doctor as a downloadable PDF.
Though Apple has not officially confirmed that the feature is available outside the US, there are sensors to enable it. All you need to do is change your region to the US and the ECG feature will work. The change in region will of course impact other settings such date/time formats, units of measurements and so on. It has to be noted that the ECG feature on the Watch Series 4 has FDA approval but it has not received thumbs up from appropriate regulatory bodies in other countries.
This approval may take a while to come. So, if you want to see how the ECG feature works, you can give it a try but if you are living outside of the US, please be aware that it has not been cleared to help detect serious health issues yet.