I am not sure about how to interface to Max MSP specifically, but it is completely possible to sync live ANT+ HRM data to a program you have written on your computer. You'll need an ANT USB Stick, and you'll need to download one of our Platform SDKs (Windows, Mac). From there, you'll be able to write a program that pulls HR data from an ANT+ HRM. You can now pipe this data to wherever you need to, as APIs allow.
Hope this helps.