Hey there, I have had several episodes where I get very cold and shivery. I associate them with a release of adrenaline prior to and during a panic attack. I also have heart issues. Not sure if the two are related though.
It sounds like you may be having PVC's or PAC's like the doctor mentioned. I used to have the "skipped" heartbeats all the time and then started taking Omega 3, 6, and 9 Fatty Acids. Since then, I only have them several times a day. I take 1 capsule three times a day...it is a gift from Above. I buy Rexall's Flax, Fish, and Borage Oil, availible in one capsule and sold at Wal-Mart. The stuff is amazing; I suggest you try it, but ask your doctor first. It has saved my life.
Omega 3 Fatty Acids are proven to stabilize cardiac cells, thus making them less excitable. This in turn can lead to a reduction in PVC's.
I am not sure what to say about the shivering. The cardiac symptoms you describe are consistent with a premature atrial beat or premature ventricular beat. The only way to know for sure is capture your heart rhythm on monitor when you have symptoms. Symptoms like this are almost always benign but if someone comes to clinic with concerns I will still do a full workup with a monitor, EKG, and echocardiogram. If they come back normal beside PVCs/PACs, your prognosis is normal. You will still have them, but there is no great cure to decrease PACs/PVCs.
I hope this helps, thanks for posting.