Since the introduction of the Apple Watch Series 4, the ECG feature is available only for Apple Watches purchased in the United States. Users from other regions only have access to the feature to purchase them in the US, but recent changes to the software have made even this workaround impossible.
It seems like this will change with the introduction of watchOS 5.2. The iOS 12.2 documentation released today, which describes the regulatory information for the ECG function, mentions that the "Apple Watch Series 4 with watchOS 5.1.2 or later" feature is available for US regions, as well as " for non-US regions "The ECG app is available on the Apple Watch Series 4 with watchOS 5.2, paired with iPhone 5s or higher with iOS 1
The addition of this mention of non-US regions with the requirement from watchOS 5.2 suggests that this is the case, with the introduction of watchOS 5.2 likely to be opened later this week for other countries.
Another extension to the iOS 12.2 update is a CE Mark, the is specific to the ECG function, indicating that the new region will be made up of countries of the European Economic Area (EEA) that accept this specific certification applies to all EU countries as well as Iceland, Liechtenstein and Norway.
The Apple Availability Features page has not yet been updated to reflect this change, but we expect it to be updated as soon as watchOS 5.2 becomes available to all customers later this week.