Could Russert's Death Have Been Prevented?

It's the question of the day: How can somebody pass a stress test and then, weeks later, drop dead of a heart attack?

During a stress test, a patient exercises to raise their heart rate. They flunk when a clogged artery prevents adequate blood flow from reaching the heart muscle. But it takes a large blockage to do that, CBS News medical correspondent Dr. Jon LaPook reports.

"But the risk of heart attack actually relates to smaller blockages that don't limit blood flow but are at risk for breaking open and having a blood clot suddenly block off the artery, as was the case here for Tim Russert," said Dr. Christopher Cannon.

In Russert's case, cholesterol built up in the linings of his arteries - not enough to affect the stress test, but enough to leave a fatty deposit that eventually burst, causing a clot that blocked the artery. About 850 Americans each day die from this condition, many without even making it to the ER. That comes to over 300,000 a year.

Clearly, a normal stress test doesn't mean you won't have a heart attack. So why do it at all?

"Well, stress tests are important to look if someone has significant limitations of blood flow to heart - if they do, then they need angiography, stenting or bypass surgery," Cannon said.

But it's not all about finding blockages after they've occurred. It's about preventing them from occurring in the first place. That's why it's key to lower risk factors such as: