Middle of breasts skin (cleavage area) lifted up why? Tenting? (Photos)

Synmastia is the appearance of your both breast as coming together too closely.  - Often called a "Uni Boob".   The cause is often over release of the sternal attachments or if submuscular - over resection of the medial segment of the pectoralis muscle.  I would review your results with your plastic surgeon.You have a really narrow chest wall, and relatively large implants for your chest wall.   But they do look like they are medially placed.  More lateral dissection maybe helpful.

Thank you for your pictures and questions. I would say that you are developing some early symmastia. From the appearance in the picture, I would bet that pre-op, you had a very wide sternum and widely spaced nipples. In an effort to create medial cleavage and fullness, your surgeon medialized the implants pockets and this led to the lateralized appearance of the nipples and the symmastia. This would likely require surgery to repair. If your original surgeon was not board certified by the American Board of Plastic Surgery or well experienced with augmentation surgery, I would suggest now would be a great time for a second opinion by someone who is. Best of luck!

Hello, if the attachments of the skin over the breast bone (sternum) are disrupted, sometimes a tented look can result which is called synmastia.  Your surgeon will be able to examine you and determine if this is the issue.

and the tented skin re-secured to your chest wall.  This would position your nipples more over the center of the mound (right now they point outwards) and allow the tenting to be fixed.  It will not get better on its own so you should be discussing your options with your surgeon and have it repaired when your surgeon decides its the right time.

You may have a degree of synmastia which may occur when using large implants, and when the operative dissection is carried too far towards the midline. From your front view it seems as if the pockets have been somewhat over-dissected inferiorly and medially (downwards and inwards) such that too much of the implant is seated below the breast meridian, and too close together. See your surgeon and perhaps get a first hand opinion.

Tenting of the skin between the breasts is usually called synmastia or symmastia. If the implants are large compared with the amount of skin or the stretch of the skin then the skin will tend to lift off the sternum.
If you are concerned about the appearance you should speak to your PS

Your results are suboptimal because your implants were not centered on you nipple and areolas. Were you trying to change breast gender as your nipple seem very lateralized; sometimes it is necessary to have a lift to try and center your nipples on your chest; you need a physical examination before making any recommendations; try to find a board certified plastic surgeon in your area.

As others have stated tenting like this can indicate at the medial edge of your implant pockets are too close together which in its worst form can be symmastia.  This can be corrected with a revision which you should discuss with your plastic surgeon.