Help using meta_value in a category__and array

I have been trying to replace ’66’ with “meta_value=issue_num” which is currently set to ’66’. It is not working. Is there a way to go about this?

I have tried: (meta_value=issue_num) and ‘meta_value’=>’value’ and still no joy. I have also tried creating global $issue=(meta_value=issue_num) and using that but still no progress.

<?php query_posts(array('category__and' => array(20,66),'posts_per_page'=>-1)); ?>