CVS Health CEO Karen Lynch has stepped down with company shares down 19% this year and the national drugstore chain struggling. Lynch will be replaced by David Joyner, who will attempt to steer the health care giant through a worsening environment of rising medical costs. CVS cut its financial expectations for the third time in August with all major pharmacy chains attempting to navigate a drastically changed landscape, facing competition online and elsewhere. Joyner, who will also join the company’s board, most recently served as executive vice president of CVS Health, and president of CVS Caremark.