that the CT scans for calcium in the coronary vessels is not really an accurate measure to predict
heart attacks.

For females, the other risks are larger. Most people do not know that you can have a spasm in a coronary vessel that kills, without plaque. Females can have this...but usually they have unstable angina symptoms before the event. These spasms can be triggered by severe stress.

I cannot comment on your question completely. But I think the soft plaque is deep in the layers of the vessel walls, instead of directly inside the lumen itself.

Arrhythmias are more common. Some are induced by drugs, and are called QT events. Some are genetic and some mixtures of both. Low potassium and low magnesium are serious causes of these as well.

Once damage occurs to the heart, conduction can be affected.
Also high homocysteine levels damage blood vessels, so taking folate/B12 and B6 can help. Viruses damage heart muscles and also high blood pressure that is untreated.
Some people have genetic errors in folate chemistry (there are 25 known polymorphisms for this) and using special folate called methylfolate can correct this. It is a silent killer.