What is Unstable Angina?

Dr. William Davis Health Pro
  • Hang around a hospital coronary care unit, and you will hear the phrase "unstable angina" used a lot.


    "Mr. Smith was admitted last evening with unstable angina."

    "Mrs. Jones has unstable angina and is going to the cath lab today."


    Just what does "unstable angina" mean? And what makes it so "unstable"?


    The term "unstable" suggests a condition teetering on the edge. And, indeed, unstable angina refers to a condition in a coronary artery that is on the verge of leading to heart attack.


    The American Heart Association lumps both heart attack and unstable angina together under the broader label, "acute coronary syndrome." Of the 1,400,000 hospitalizations in the U.S. every year for an acute coronary syndrome, 810 000 are for heart attack, and 537,000 for unstable angina. (The remainder is due to a combination of the two.)

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    Heart attack, or more properly, acute myocardial infarction, occurs when an artery of the heart closes off completely, leading to damage to a portion of the heart muscle. The process begins with an atherosclerotic plaque in the artery, regardless of whether it is "only" a 20%, 30%, 40%, or 90% blockage, that "ruptures" like a little volcano. However, lava doesn't erupt, but the internal contents of the plaque - cholesterol and fat, inflammatory cells, structural tissue, calcium - are exposed to flowing blood. Exposure of plaque contents triggers blood clot formation. The blood clot quickly grows and can completely close off the artery: heart attack.


    Unstable angina arises from an identical process. But, rather than completely closing off the artery, the artery is only partially closed to, say, 90%. Blood still manages to squeak by. Though the remaining opening may be 10% or less, the blood clot is still there, along with the ruptured plaque underneath it. The artery can close off at any moment, depending on the balance between clot formation and dissolution, a balance that differs based on many factors. It is therefore an "unstable" situation that, if the scale tips in favor of extending the blood clot, could proceed to heart attack.


    Unstable angina is bad news. It means that you have coronary artery disease and you are on the edge of having a heart attack. However, the "advantage" of unstable angina versus a heart attack is that no heart muscle damage has yet occurred. It means that there is still time to institute medicines and other treatments that can keep the unstable ruptured plaque from closing and ending in heart attack. 


    So the difference between unstable angina and heart attack is literally a millimeter or less, the amount of artery flow remaining through the area of ruptured plaque.


    What factors keep the unstable ruptured plaque from closing? Mostly factors that affect the ability of blood to clot. This is why strategies that thin the blood can be helpful to prevent heart attack, strategies that include aspirin (that blocks clumping of platelets, cells in blood that make clots grow); omega-3 fatty acids from fish oil (that promote  blood thinning by a number of avenues, including blocking platelet clumping); hydration (keeps blood viscosity low); exercise and healthy eating (that reduce unhealthy blood clotting proteins, such as fibrinogen).


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    Let's unwind the process one step further: What keeps the plaque from rupturing in the first place? That's yet another topic for a future post.


Published On: February 18, 2009