The former Championship side currently sit in ninth in the league table, four points away from a Champions League position.
"At the start of season, we had a few meetings where we talked about where we would want to be after eight games or so and we are very happy to have surpassed that," McCartney told the club's official website.
"We have started off really well. We have picked up some really good results which has resulted in us sitting in the top half of the table, but there is a long way to go yet in the season and we must make sure we continue as much as we can what we have started."
The Hammers are preparing to take on Manchester City this weekend.