SelectionPattern.InvalidatedEvent, champ

///--------------------------------------------------------------------
/// <summary>
/// Subscribe to the selection events of interest.
/// </summary>
/// <param name="selectionContainer">
/// Automation element that supports SelectionPattern
/// </param>
///--------------------------------------------------------------------
private void SetSelectionEventHandlers
    (AutomationElement selectionContainer)
{            
    AutomationEventHandler selectionInvalidatedHandler =
        new AutomationEventHandler(SelectionInvalidatedHandler);

    Automation.AddAutomationEventHandler(
        SelectionPattern.InvalidatedEvent, 
        selectionContainer, 
        TreeScope.Element, 
        SelectionInvalidatedHandler);
}

///--------------------------------------------------------------------
/// <summary>
/// Selection invalidated event handler.
/// </summary>
/// <param name="src">Object that raised the event.</param>
/// <param name="e">Event arguments.</param>
///--------------------------------------------------------------------
private void SelectionInvalidatedHandler(object src, AutomationEventArgs e)
{
    // TODO: event handling
}