I am sorry it took me so long to get back to you. I have been away for a few days. I looked at the links you posted, and I really think rodenticide poisoning is pretty unlikely. Unless you had rat poison set out somewhere in your house, there really is no way Tiger would have had access to it. I can't imagine the food was a major factor either.
Certainly, heart disease and saddle thrombus is a possibility. I would, however, have thought that they would have found an enlarged heart if that was the case. You can also visualize a clot in a vessel on the autopsy if you are looking for it.
A clotting problem is still a possibility, even though there was no free blood in any body cavity. They can get something called immune mediated thrombocytopenia, and you might not actually be able to prove it on autopsy. There usually isn't free blood in the chest or abdomen. Usually you see bruises, pinpoint bleeds in the eyes and in the mouth. Here is a link about this problem.
This can actually come on fairly quickly in some cases, and might have presented as sudden death, like you witnessed.
Electrical cord burn is not impossible, even though it may seem unlikely. Truthfully, I think it is more possible than a rodenticide poisoning. They don't have to be near the chewed cord, as some of the effects build-up and death can be delayed. If a cat were chewing a particular cord, the shock could cause small hemorrhages, frank bleeding and severe consequences for the respiratory and circulatory system. They may not occur or even be immediately apparent.
I wish I could give you some definitive answers, but unfortunately, you may never know exactly what happened. If you have more questions, just reply and I'll get back to you as soon as possible.