Assuming you're using an up-to-date compiler:
if (dgvMenu.Rows[_selectedIndex].Cells[3] is DataGridViewLinkCell linkCell)
{
bool linkVisited = linkCell.LinkVisited;
...
}
For older compiler versions:
var linkCell = dgvMenu.Rows[_selectedIndex].Cells[3] as DataGridViewLinkCell;
if (linkCell != null)
{
bool linkVisited = linkCell.LinkVisited;
...
}