Is Unstable Coronary Artery Disease More Common Than We Thought?

As part of a research study, investigators measured blood troponin levels in over 7500 consecutive patients just before they had elective angioplasty and stenting for clinically stable coronary artery disease (CAD). To the investigators' surprise, over 6% of these apparently stable patients had elevated levels of troponin, indicating cardiac muscle damage. And in addition, those with elevated troponin levels had twice the risk of heart attack or death over the next year.

Troponin is an enzyme that is released into the bloodstream when cardiac muscle cells are dying. Elevated troponin levels usually mean that blood clots are forming in the coronary arteries at the site of a plaque. Blood clots that form and then dissolve quickly usually produce unstable angina, whereas blood clots that form and do not dissolve cause myocardial infarctions, or heart attacks.

The findings of this new study, reported in the journal Circulation this week, strongly suggest that some patients with apparently stable CAD actually are quite unstable. That is, they have "vulnerable plaques" which are generating transient blood clots that are causing heart cell damage. Furthermore, those who have these vulnerable plaques are far more likely to have heart attacks or to die than patients whose CAD is actually stable.

The next step will be to conduct larger studies to confirm that this finding is true. If so, researchers will then look for methods to screen more routinely for patients who apparently have stable CAD but who actually have a much more dangerous condition. Read more about unstable CAD here.

_Sources:

Jeremias A, Kleiman NS, Nassif D. Prevalence and prognostic significance of preprocedural cardiac troponin elevation among patients with stable coronary artery disease undergoing percutaneous coronary intervention. Results from the evaluation of drug eluting stents and ischemic events registry. Circulation 2008; DOI: 10.1161/CIRCULATIONAHA.107.752428.