There are a couple of ways to handle the ANT+ situation.
Apple does not support ANT+ on the iOS or tvOS platforms. In order to use ANT+ devices in the Apple world, you will need an additional device to bridge the ANT+ signals and convert/rebroadcast them as Bluetooth LE. Such bridge devices are the 4iiii Viiiiva heart monitor and the NPE CABLE.
The bridge device can convert/rebroadcast the ANT+ signals of several devices, such as heart monitor, cadence sensor, etc. The BLE connection from the bridge to iOS is a single BLE connection but with multiple services (one for each ANT+ device being bridged).
There’s some info with some links in this article:
Scroll down to the “ANT+/BLE Bridge or Receiver” section.
Another option would be to buy a new heart monitor which supports both ANT+ and BLE. An example would be the Wahoo Tickr HRM’s which are dual-band. The Viiiva also is dual-band, in addition to being a bridge.
I have an older Garmin HRM which is ANT+ only [and also have a Garmin cadence sensor]. I’ve been using the NPE CABLE for well over a year with no issues. It has worked great with both my iPad and AppleTV to convert the ANT+ signals to Bluetooth.
Best of luck! And ride on!