Are you showing any signs of infection - redness and persistent swelling at or around the knee, elevated fever, flu-like symptoms? Infection from a TKR is rare - 1% of cases - and I think you'd know if you had an infection at the surgical site. 59 to 62 is a very good resting HR and you're experiencing about a 25% increase.

I didn't monitor my HR after my TKRs so I'm afraid I'm not much help. Ladybug makes an excellent point that anxiety and pain can raise heart rate. The stress of PT and daily rehab could also be raising your HR.

It's been 4 weeks though so your pain levels should be a lot lower than the first two weeks. In any case, check with the doc.

All the best.