[Calavar]

Personal history.

"Many" is relative. We are talking about a fraction of a percent of the general population, but if you are looking specifically at the population of people who have some form of long standing heart disease, it's not terribly rare. I don't work in cardiology specifically, and even so I encounter one or two patients a year who have had an ICD placed for reason #3.

Persistent risk factors include things like or overgrowth of muscular heart tissue (which has dozens of causes, but the most common is severe, long standing coronary artery disease) or scarring of the heart after a heart attack.

Persistent risk factors are not rare at all. The thing is that most people who fall into bucket 3 also fall into buckets 1 or 2. So in an ideal world they would have already seen a cardiologist and had an ICD placed before they ever had an episode of SCD. And of course many of those who do have SCD don't survive long enough to have an ICD placed.

If you are interested in reading more, you can search for "secondary prevention of sudden cardiac death" or "secondary prophylaxis of sudden cardisc death." There are some good review articles available online.