array_shift but preserve keys

array_shift but preserve keys

My array looks like this:
$arValues = array( 345 => "jhdrfr", 534 => "jhdrffr", 673 => "jhrffr", 234
=> "jfrhfr" );
How can I remove the first element of an array, but preserve the numeric
keys? Since array_shift changes my integer key values to 0, 1, 2, ....
I tried using unset( $arValues[ $first ] ); reset( $arValues ); to
continue using the second element (now first), but it returns false.
How can I achieve this?