Wednesday, April 11, 2012

When risk scores for heart attack really suck!

When risk scores really suck.

If you are a man aged 55 or younger, or a woman aged 65 or younger and have had your risk for heart attack and stroke profiled recently, chances are your doctor told you that you have a low risk. So you probably walked out of her clinic, seeing no reason to change your lifestyle. Now here I am, the party pooper, who is going to rain on your parade. How so?
Well, first off, those risk scores, like the Framingham score used in the US and the PROCAM score used here in Germany, typically look at things like cholesterol, blood pressure, blood sugar, smoking status, age and gender. From these values the scores determine your 10-year forward risk. Conventionally, if your chances of suffering a heart attack, stroke or any other of the cardiovascular diseases endpoints is less than 10% for that 10-year period, yours is categorized as low-risk. If it was in excess of 20%, you would be considered a high-risk person, and anything in between is called moderate risk. Now here is the problem: of the women who are hospitalized for their first heart attack at an age younger than 65, typically none would have scored as high-risk even a day before the event [1].  In fact, 95% of these women would have flown under the risk radar in the low-risk altitude.
How come, you may ask. To understand the reason you need to know how heart attacks and strokes happen. Most of them are the result of a blood clot being formed at the site of a ruptured plaque (those fatty streaks) in one of your arteries. Traveling downstream these clots may be dissolved or they may be not. If they get stuck some place downstream, blocking the supply of blood, and thereby of oxygen, to your heart or brain tissue, a heart attack or stroke occurs. But most plaque ruptures do not cause a heart attack or stroke. There is a large element of chance involved. Fact of the matter is, we can't really predict which plaques will cause a heart attack or stroke. We can't even say whether a stable or a so-called vulnerable plaque will still be stable or vulnerable in a few months down the line. They can change their status. Which means, even if your doctor was able to map all the plaques in all the arteries throughout your body, he still wouldn't be able to tell you exactly your risk. How much less accurate will his risk prediction be when he uses risk factors which just correlate somewhat with plaque burden, such as cholesterol? There you go.  
Which is why you should not look at 10-year risk, but at lifetime risk. For a woman that risk stands at roughly 40% once she has reached the age of 50 [2]. Men, by the way have a 52% risk at that age. But here is the kicker: being free of any of the risk factors (those of the Framingham or PROCAM variety) at that age, means a dramatically lower lifetime risk of 8% and 5% for women and men respectively.
So here you are. Your doctor has just sent you off with a low-risk assurance for the next 10 years, even though 2 of your risk factors are elevated. You walk out of his clinic with a strong sense of invulnerability and no real motivation to change your lifestyle and to get those two risk factors back into the green zone. That's why risk scores really suck. When they rain on your parade later on it's a lot worse than if I, the party pooper, do it right now. Don't you think?

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