Are TENS nipple electrodes safe??

I touched on this in a previous post, but is anyone reading this knowledgeable about whether TENS type electrical play can be done safely on nipples?

I have done TENS play below the waist and LOVED it, and I adore attention to my nipples. However, there are a lot of cautions out there about not playing above the waist for fear of stopping the heart.

This article concludes that it is safe, at least with a typical TENS unit:

http://rurubound.wordpress.com/2012/...ove-the-waist/

Anyone care to weigh in authoritatively on whether this is safe or not? Or safe if done only on one nipple? Unipolar vs bipolar electrodes? Etc., etc.

Oh, and if TENS isn't safe for nipple play, why is it safe in a non-sexual context to use TENS to stimulate lactation in new mothers, muscle pain in the chest in back, and even angina (chest pain from coronary artery disease)? The devices appear to be exactly the same.

I don't use them above the waist.