You are confused about the difference between an array and an arrayref and a "$" and an "@". "@row->[0]" doesn't mean anything, that's not how either arrays or arrayrefs are referenced. You need something like this, but this is only a guess since you don't really tell us what you want to do.

my $m_dbh = DBI->connect("DBI:mysql:...);
my $a_dbh = DBI->connect('dbi:AnyData(RaiseError=>1):');
$a_dbh->func( 'cars', 'CSV', 'testperl.csv', 'ad_catalog');
my $pats = $m_dbh->selectcol_arrayref("
    SELECT PAT FROM patentes
");
my $pats_str = join ',',@$pats;
my $a_sth = $a_dbh->prepare("
    SELECT * FROM cars WHERE PAT IN ($pats_str)
");
$a_sth->execute();
while(my $row = $a_sth->fetch){
    print "@$row\n";
}
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