Run "show slave status" with PHP PDO

I am trying to get the slave status of my MySQL server using PHP's PDO implementation. Running fetchAll() returns an empty array.

// DB IP, name, username, and password are fake here. I can connect.
$db = new PDO('mysql:host=192.168.0.0;dbname=production', 'username', 'password');
$result = $db->query("SHOW SLAVE STATUS");
$result->execute();

if ($result != false)
{
    $slave = $result->fetchAll(PDO::FETCH_ASSOC);
}

I have also tried removing the ->execute() call, but it's the same result. Is there something completely obvious that I'm missing here? I've looked up and down the PDO::query documentation and it's not helping much.