flash actionscript: Hi I have this code:

var myvar = new LoadVars();
myvar.action = "getSlides";

my problem is that I need to set variables for the LoadVars object
dinamically, like for example

var mytestvar = "action";
var myvar = new LoadVars();
myvar["mytestvar"] = "getSlides";

I thougth the above code should work, but not, anyone knows how I can set the
variables dinamically

thanks for any help

var mytestvar = "getSlides";
var myvar = new LoadVars();
myvar.action= mytestvar;