With youngish people, it's congenital heart defects that cause the heart to stop. Happens all the time, mostly during endurance exercise, e.g.

https://www.theguardian.com/sport/2018/apr/09/michael-goolae...

I guess it's scary, but people do drop dead. I was working at a startup once, and in my monitor reflection, I see the guy behind me drop to the floor. He started convulsing, and then was still. We called the paramedics, but the next morning we learned he had died. That was it. No warning. An otherwise healthy guy. You never know when it's going to be your day.

Don't know, I think it could mean a lot of things. You usually read about it when healthy young persons drops dead on a football field in the middle of practice. Saw some numbers about it recently, happens a lot.

I believe the medical term is "cardiac arrest". It is different than a heart attack. Something caused the heart to stop beating.

They coded my brother as SCA (sudden cardiac arrest).

This happens all the time. It happened to my dad, who was healthy and exercised regularly. After a bike ride he collapsed and died.

Often there are warnings, like arythmias which I guess can be signs the electrical functions aren't great. Those sorts of congenital defects are hard to detect, acknowledge and treat seriously as a condition.

Wolf-Parkinsons-White

aka "sudden death syndrome"

Some people have heart defects that leave them susceptible to instant surprise heart failure.

A notable case is a college basketball player a few years ago who literally just died running across the court.

My wife has this!

cardiac arrest, it's pretty rare but still scary. Over 400k Americans die from it every year.

400k doesn't sound so rare. The entire population of Tulsa OK, Wichita KS, or New Orleans, LA just drops dead every year?

ROC – Resuscitation Outcomes Consortium datum were gathered between June 1, 2014 and May 31, 2015 and includes EMS-assessed and EMS-treated out-of-hospital cardiac arrest from multiple regions of the US.

According to the ROC:

Approximately 356,461 people in the US experienced an out-of-hospital cardiac arrest (347,922 adults, 7,037 children under age 18)

22,520 of those 356,461 were witnessed by bystanders

12.4% survived to hospital discharge

Of the EMS patients who experienced non-traumatic cardiac arrest outside a hospital, and did not have bystander intervention, 10.8% survived until hospital discharge

[999] - https://www.aedsuperstore.com/resources/sudden-cardiac-arres...

It's rare in young healthy-acting people.

For example, http://www.sca-aware.org/sca-news/aha-releases-2015-heart-an... says that the incidence is 0.24 per 100k annually for high school athletes in Minnesota. Extrapolating that rate to the whole US population would give ~800 deaths per year. The observed 400k number includes quite a lot of people who suffer cardiac arrest after a history of heart disease.

If this is a topic you'd like to know more about or donate to, consider: https://viaheartproject.org