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.
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!