VO2 kinetics and HR aren’t connected (not really). There are lots of parts that go into a VO2max interval, I do my best to keep it as simple as possible. HR is used only as a pseudo-proxy for the process as it (>90% HRmax) correlates somewhat well for most people.
Not sure what it means if your HR is reacting that fast, and rising at threshold power to a level similar to VO2max power. I suspect neither scenario is a perfect one. 