Been a while
Hi [First name],
It has been about a year since your last visit with us. No pitch in this one. I just wanted to check in and say the door is open whenever you want to come back.
If you would rather not hear from us, unsubscribe below and we will leave you alone.
[Clinic name]
Why it opens with nothing. The first message after a year of silence is not the place to sell. It re-establishes that a person works here, and it gives an easy way out, which is what keeps the next two out of the spam folder.