Tension has been increasing within the team in recent months, according to eight people familiar with the situation.
The early-stage study took place over 12 weeks and included an 82-person healthy control group and 31 individuals with varying stages of cognitive decline.
New capabilities include women cycle tracking, Noise app, Activity Trends and App Store right on the wrist; also, there are new watch faces.
The Cupertino-based company has a few key advantages over its technology rivals, including privacy and the huge base of iPhone and Apple Watch users.
Such technology would enable owners of future iPhones and Apple Watches to detect things like spoiled food, body odor and perhaps even blood sugar levels.
Part of the watchOS 5.2 update, the ECG app can capture heart rhythm in a moment when users experience symptoms such as a rapid or skipped heart beat.
The largest study ever of its kind enrolled over 400,000 participants from all 50 states in a span of only eight months.
Once ready, it will let American veterans receiving care through the Veterans Health Administration view their aggregated health records on their iPhone.
The first Apple-branded sleep tracking device may be around the corner; it will likely be an incremental update, mind you.
Announced as one of key features of Apple Watch Series 4, the ECG functionality will be released by the end of the year as part of the next software update.