Wireless sensor and actuator networks bring many benefits to industrial automation systems. However, unreliable wireless and multihop communications among sensors and actuators cause challenges in designing such systems. Wireless HART is the first standard for wireless real-time industrial applications. However, current Wireless HART standard does not provide services for efficient usage of actuators, which are an essential part of automation. In this paper we focus on Wireless HART and propose a periodic and deterministic downlink transmission functionality which enables efficient usage of actuators and control applications. Furthermore, we define new HART commands extending the interface, without affecting available services, to support the integration of actuators. This can be achieved with minor changes in the current standard.