Plaques that kill without warning
Every year, some half a million patients die of a heart attack, and while many had known heart disease, an alarming number may have just received a cardiovascular clean bill of health from their doctors.
“About half the victims die suddenly, without previous symptoms,” said Peter Libby, chief of cardiovascular medicine at Brigham and Women’s Hospital in Boston.
Researchers have come to realize that most sudden heart attack victims harbor a stealth danger -- “vulnerable plaques” embedded in the arterial wall that largely defy detection.
These are not the plaques most of us are familiar with from discussions of blocked arteries. Those are stable, fibrous plaques -- made of fat, cholesterol and other substances -- that turn the shiny white surface of a healthy artery milky white. Like the hard-scale buildup in pipes, fibrous plaques can restrict blood flow and harden the arteries. But they usually don’t dislodge to form a life-threatening clot.
Vulnerable plaques, on the other hand, appear yellow and squishy. They consist of a pool of lipids in the artery wall covered with a thin fibrous cap made of smooth muscle cells and collagen. The cap and surrounding vessel wall also contain macrophages, the immune cells drawn to damaged cells that cause inflammation.
It’s these plaques that are often the ticking time bombs of heart disease.
“When the thin protective cap cracks open, like a pimple popping, it exposes a core that is crammed with cholesterol and inflammatory cells, and those inflammatory cells contain triggers for blood clotting,” Libby explained. “It’s counterintuitive, but tight narrowings of arteries do not cause most heart attacks. Clots cause heart attacks.”
Said Dr. Gregg Stone, director of research and education at the Center for Interventional Vascular Therapy at New York-Presbyterian Hospital/Columbia University Medical Center: “If we could identify patients that have the vulnerable plaques and could tell which ones are likely to rupture, and design therapies to prevent it, we could save hundreds of thousands of lives.”
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Researchers are exploring ways to distinguish vulnerable plaques from less dangerous fibrous ones -- which might eventually lead to better prevention strategies. Also, what we know so far about how to prevent the plaques.
