Well not sure what version you are running but you can do this in InnODB as well with MySQL 5.6.
If you run Explain EXTENDED SELECT ueberschrift ......
you will then see the filtered column.
More on that can be found here
http://dev.mysql.com/doc/refman/5.1/en/explain-output.html#explain_filtered
You can add a key to the table for kat.
KEY `kat` (`kat`)
You can force that index FROM artikel_Mode FORCE INDEX(kat) WHERE
You of course would have to run explains on those to see if it actually helped compared to your original.
But first... Why is kat varchar if you have all INT in it?
`kat` varchar(12) NOT NULL, why not `kat` int(10) DEFAULT 0,
ALTER TABLE artikel_Mode CHANGE kat `kat` int(10) DEFAULT 0;
Just trying to help....
http://anothermysqldba.blogspot.com