Yes, that was what I was told when I had to get mine. I think that is a good rule especially following a MI like mine. When you have idiopathic cardiomyopathy many times the heart might recover. I once had that and a EF of about 35% but they of course didn't rush me to get an ICD. After about 11 months my heart was back up to 55% or so.
The strangest thing was that after my heart attack they did an echo about 4 days after and my ejection fraction came back 40%. They then sent me home without an ICD. Then about 4 weeks later I had another echo and it came back below 20%. I was feeling much better by then too, symptoms were a lot better. I never did get a good answer for the discrepancy. It almost ended up killing me because I was doing squats and went into VT. We called the paramedics and they had only been here maybe 2 minutes and I went into cardiac arrest. They had to shock me 2x to get my heart going again.
I should have had an ICD when I left the hospital. I think something was wrong with that first Echo. I was either still on dopamine or just gotten off of it. Maybe that had my EF artificially raised?
Oh, sorry to hijack your thread!