Get Item/Product Attribute in WooCommerce Order

I'm trying to get Item or Product Attribute in WooCoomerce Order.

How can I get it?

$order  = new WC_Order( $order_id );
$items  = $order->get_items();

foreach ( $items as $item ) {
        $pid    = $item['product_id'];
        $patt   = $pid->get_attribute( 'pa_myattrname' );
        echo $patt;
}

Later, I want to insert autoresponder link on attribute, so that after user complete payment, they will automatically subscribed into my autoresponder.

Thank you

via Chebli Mohamed