A recent report has said that Apple would bring "a killer device" to market in 2017, but plans for the future can change at any time. And even when evidence is presented that "confirms" a claim, initial evidence needs further evidence before it can be deemed probably credible. Apple's claims to bring a new device to market in 2017, though, may have some new evidence to give credence to the statement.
A new patent discovered by Patently Apple shows a wearable device that can be worn on the wrist or ankle and measures electrocardiographic (ECG) activity. Apple's wearable is unique, not because it measures heart rate activity (this nothing new for wearable devices) but because it can correct an inverted electrocardiographic measurement if a device is worn on a limb that's further away from the heart than a limb that's closer to it. Before wearing the device constantly, the new Apple patent would mandate users to place the ECG device on a few body locations so as to give the device time to properly calibrate measurements. You can see patent drawings below.
Apple has filed a patent for a curved wearable display, and a fitness wearable that would measure heart rate seems to be a good use for a curved wearable (after all, wearing a device on the wrist should induce comfort, not discomfort, and curved wrist wearables tend to win the war on comfort). Apple has said that the device could be something similar to a smartwatch but the fruit company doesn't want to do battle with the FDA over a smartwatch. This device could indeed be a heart rate monitor, fitness-tracking device of some sort (something akin to "Apple Fit" as a working moniker for the upcoming device).