Adding annotations synchronously

I have a method that adds a marker line to my chart. The issue I have it that calling this method results in a non-blocking async call but in other code where I call this, I want to access the markers immediately after adding the marker. Is there a way to call Annotations.Add synchronously?

public void CreateNewMarker(DateTime markerDate, Color color)
{
try
{
MainChart.Annotations.Add(new VerticalLineAnnotation()
{
Stroke = new SolidColorBrush(color),
StrokeThickness = 1,
X1 = markerDate,
StrokeDashArray = new DoubleCollection(new List { 6, 3 }),
IsEditable = false
});
}
catch (Exception ex)
{
Tracing.TraceError(piuModule, className + “.CreateNewMarker()”, “Error during the CreateNewMarker() method”, ex);
}
}

Other Method
{
calls CreateNewMarker(0
Access new marker Annotations by index, MainChart.Annotations[markerIndex].X1

}