public MainWindow()
{
    InitializeComponent();
    gcSpread.PreviewMouseWheel += GcSpread_PreviewMouseWheel;
}

private void GcSpread_PreviewMouseWheel(object sender, System.Windows.Input.MouseWheelEventArgs e)
{
    if (Control.ModifierKeys == Keys.Shift)
    {
        GcSpreadSheet gcSpreadsheet = sender as GcSpreadSheet;
        gcSpreadsheet.SetViewportLeftColumn(0, gcSpreadsheet.GetViewportLeftColumn(0) - (e.Delta / 120));
        e.Handled = true;
    }
}