Can a thread lift be used to treat tear troughs that go completely across the cheeks? (photo)

The kind of elongated tear trough you show in the photo is something that experienced injectors see practically every day and can easily improve by the use of an injectable volumizer, such as Voluma XC for the malar (cheek) region and which, when injected properly, secondarily improves the tear trough (often without any need to inject the tear troughs directly with filler).  The results of this treatment typically result in an immediate "Wow!" reaction.  So, why not threadlifts. Well, in a recent February, 2019 issue of Aesthetic Surgery Journal, examining threadlifts, researchers found that not only did the results of the threadlift not last significantly more than six months (and were gone by one year), but that complications, such as infection, facial stiffiness, skin dimpling, etc. were experienced by more than one third of the subjects studied. The authors of the study concluded, therefore, ""Given the transient benefit and the complication rate of 34%, we recommend limiting this procedure..." Make sure that you consult with an experienced board certified aesthetic physician and ask to see his/her personal before and after photos before agreeing to proceed. Best of luck. 

In your age it is best to treat these small deficiencies with fillers. Tread  lift is not procedure for that. Consultation with a board certified plastic surgeon is recommended. Good luck.

You look to be a really good case for the use of fillers . You can use a combination of lifting threads and smooth threads to treat this area but frankly you are going to get a much better result with fillers. 
Find an experienced injector and talk with them about your options in treating this area. Don't be surprised if they suggest filler not only in the tear trough but midface and cheeks as well.