Heart Protein Predicts Future Attack
High levels of troponin call for aggressive therapy, says study
WEDNESDAY, Nov. 14, 2001 (HealthDayNews) -- Raised levels of a protein that helps the heart contract indicate you've had a heart attack and that you're likely to have another one within the next 30 days, says a new study.
The finding clears up some confusion over the significance of elevated levels of the protein troponin and whether doctors should take dramatic measures for a patient with the symptom. The level of troponin is a reliable indicator of heart muscle damage, and, more importantly, it indicates a patient's risk of a future heart attack, says the study by researchers at Duke University Medical Center, in Durham, N.C.
The findings were presented yesterday at the American Heart Association Scientific Sessions 2001 in Anaheim, Calif.
Every year, roughly 1.1 million Americans have a heart attack. About 650,000 will be first-time attacks, and 450,000 will be recurrent attacks. More than 40 percent of the attacks will be fatal, making coronary heart disease the leading cause of death in the United States.
The research grew out of confusion among doctors over how best to treat cardiac patients with various levels of troponin and creatine kinase-MB, proteins released into the blood when heart muscle cells are damaged or die. While doctors knew that positive tests for both proteins meant they should treat the symptoms aggressively, raised levels of only one protein were less helpful.
Lead study author Dr. Sunil Rao, a cardiology fellow at Duke, wanted to know if the blood tests could be used to determine whether patients were at a higher risk for another, larger heart attack or death.
Rao and his colleagues compared data from three large-scale trials, dividing patients into groups: those with high troponin and CK-MB levels and those with high levels of only one of the proteins.
Regardless of whether patients had acute or mild coronary symptoms, the researchers found that troponin levels alone pointed to an increased risk of another heart attack or death 30 days after the first attack.
"If you have an elevated troponin but a normal CK-MB, we should probably treat you as if you're having a heart attack," says Rao. This involves putting patients in cardiac intensive care and using aggressive treatments, such as cardiac catheterization, to determine whether they should have surgery.
Other studies suggest that aggressive therapies may reduce the rate of recurrent heart attacks and death, says Rao.
Dr. Sidney Smith, chief scientific officer of the American Heart Association, says there is growing recognition of the value of troponin levels in identifying patients who may be at risk.
"CK-MB was the old standard, and this trial showed that when troponin was up, the 30-day mortality in patients that came in with acute coronary syndromes was the same regardless of what CK showed," says Smith.
"The data in this study and others provide a growing base of evidence that troponin should be used to risk-stratify patients with acute coronary syndromes. When troponin is up, irrespective of other markers, we should consider these patients at high risk," says Smith.
All patients with coronary symptoms should be tested for troponin levels, Smith says.
Rao says troponin is released into the bloodstream within six hours of damage to the heart muscle.
"The other advantage of it is that it lasts in the bloodstream for seven to 10 days," he says. If a patient has chest pain but doesn't go to a doctor for several days, Rao says a positive troponin test can still point to heart damage. CK-MB levels peak roughly 12 hours after a heart attack and disappear within a day of the event.
However, Smith says because troponin stays in the blood for so long, it can be hard to figure out if there's been more than one coronary problem.
Rao notes that troponin also is released if the heart muscle is damaged by trauma, such as a car accident, but he says a patient's history can rule out whether trauma is a factor.
What To Do
The American Heart Association provides information on blood tests for heart attacks.