Heart palpitations can often be a sign of food allergies. I recently had allergy sensitivity testing and one of the signs of an allergic response to foods is palpitations. I have headaches from aspartame and palpitations with other foods. I'd say that you corresponded the response to the cause very well!
It is conceivable that certain foods trigger PVCs in certain individuals. It is also possibly a coincidence. If the aspartame had been the cause, I would not have expected it to take two days for the palpitations to go away, as your body would have excreted the aspartame much sooner than that. However, I would say to go with whatever works for you.