Format: 

In-text only: (A. Author, personal communication, Date of lecture)

Author, A. A., & Author, B. B. (Date of lecture). Title of lecture [PowerPoint Slides]. Retrieved from URL

Examples: 

Horowicz, K. & Nicosia, L. (2015). ARTstor: More than just art! [PowerPoint slides]. Retrieved from http://mycourses.rit.edu

In-text: (Horowicz & Nicosia, 2015, slide 3)

Notes: 

Note: PowerPoint slides are not usually retrievable by others outside of the class so do not need to be included in the References list. Instead, include an in-text citation for personal communication and provide context within the body of the paper. If your professor requires that you cite class PowerPoint slides posted to MyCourses or if your PowerPoint is posted online outside of MyCourses, use the format in the second example.

Source:
APA (ER) - p. 31