peculiar leg pain after cardiac ablation for atrial.fib

I am almost 3 weeks post-procedure and have a slowly-healing large painful hematoma in my left thigh. But I also have this wierd pain syndrome: when I change the position of my knee from flexion to extension or vice versa (e.g.if I'm sitting in a chair or my car awhile and then stand up) nothing happens for a few seconds, but then there is a slow crescendo of squeezing or intense  aching pain in the lower thigh and down into the knee that builds over maybe 30-45 seconds and then tapers off. Is this familiar to anyone?

[Cleveland Clinic]

The most concerning event is that your hematoma is placing pressure over the femoral nerve and then causing the pain you are referring to. Another possibility is that you have a deep venous thrombosis causing these symptoms in the calf, relating to venous hypertension. I would suggest an ultrasound of the legs in both cases to determine whether or not you have any of these. I am assuming the operation was performed on coumadin, but if not then the risk of the second complication is greater.