Moving Annotations by Code

Hi guys, i have a question regarding Annotations in WPF.
I use Oxyplot to show an overview of values over a span of time while i play them back. Thus, i need an indicator for where the current time of the playback is.
is this possible?
i thought i would use a VerticalLine and move it to CurrentTime at every call, but i can't get it to run, it just freezes.

I also want to avoid redrawing the entire plot each time (~20 times a second) if possible, because i only need to move the one annotation.
I would be thankful for any pointers, thanks.