Thankyou , I have not had the ECG or IEKG. I will be talking to my Cardiologist .
You mention a heart doctor (cardiologist?) and a stress test. My understanding of a stress test, I've had several, most nuclear stress tests, is to check on how well the blood is getting to heart muscles. Given you got good results on the stress test (here stress refers to physical stress on the body/heart, not mental stress) it is unlikely that you have any blockage - that's good.
You didn't mention EKG, but you did have a holter monitor. THe holter is good for catching irregular heart activity, but the EKG is better at taking a "snap shot" of the heart's electrical makeup. Have you had an electrocardio gram IEKG/ECG)? If not, I think you should discuss this with your heart doctor.
I understand that difficulties in dealing with emotion stress, anxiety, depression can cause heart palpatations. Has you doctor suggest trying any medications to reduce any of these conditions? If treating one or more of those problems returns you heart to normal rhythm, then you know what the problem is, otherwise it seems to me such causes are conjecture.