cause of dcm

Recently diagnosed with dcm, with ef in the 40s. Found during angiogram.  Arteries clear, with no blockage.  Bradycardia, low pulse, very low chlosterol (140 total), but very high hdl (90).  Two days before had ex stress/sonagram, with af after raising pulse on treadmill from 47 to 154. 70 years old , 73 inches, 200 pounds. Lots of cv exercise for decades.  Bradycardia for at least 30 years.  one known incident of fast pulse (to 80) three weeks bef ex stress test.
What is best way to det cause of DCM?  Can af be likely cause of DCM? (Very little alcohol, no drugs, fair amount of stress, ex diet)  What about resveratrol(400mgs)?  Virtual "groupie" in Sinclair Harvard resvetrol studies.  If not af-caused, what is best way, if any, to det likely cause?  Completely in the dark, and would appreciate any--any--advice.  Thanks!

[Cleveland Clinic]

There is often no way to determine the cause of the diminished EF, or DCM as you call it. But it really does not matter because, unless in rare instances where it is caused by an acute inflammatory myocarditis ( gialt cell) it is treated using the same medications regardless of etiology. You should be on a beta blocker, ace inhibitor, possibly a baby aspirin and if symptoms of heart failure develop possibly an aldosterone blocker. Additionally, you may need protection from sudden cardiac death from a defibrillator.