Blood levels of the enzyme creatine kinase-MB (CK-MB) rise after a heart attack, indicating injury to the heart muscle. Measuring CK-MB is a standard diagnostic test for heart attacks. Several studies have shown that elevated CK-MB is a marker for minor heart attacks and an increased risk of cardiac death after angioplasty and other catheter-based procedures. However, the nature of the relationship between CK-MB and adverse outcomes after angioplasty remains controversial.
Researchers in this study found that people with CK-MB levels more than five times higher than normal after angioplasty or stenting have a "clinically significant" increased risk of death for three to four months after the procedure. This was particularly true for those with other risk factors such as advanced age, heart failure or kidney failure.
Study author Stephen Ellis, M.D., a study author and professor and director of invasive cardiology at the Cleveland Clinic Foundation in Ohio, says the study is one of the largest of its kind. It produced several new findings: (1) a clinically significant risk of death is associated with CK-MB levels greater than five times normal; (2) there is an early period of risk, which appears to extend three to four months after the procedure; (3) the risk is greatest for patients with the highest CK-MB levels, kidney failure, heart failure, incomplete revascularization, advanced age, and high post-procedural C-reactive protein; and (4) treatment with a statin drug may lower the risk of death after a procedure.
"From the clinician's perspective, a major question has been what to do with patients who have an increase in CK-MB after angioplasty," says Ellis. "Our data show pretty clearly that if the CK-MB elevation is less than five times the upper limits of normal, particularly if the rise is not associated with any other risk factors, then it is quite safe to discharge the patient in the usual fashion, which is the day after the procedure," he says.
"In addition, patients who have higher than five times normal CK-MB levels should probably only be considered for longer hospital stays if they are in a high-risk group," says Ellis. "These patients should also be strongly considered for statin therapy."
Investigators evaluated data on 8,409 patients (average age 65) who had successful catheterization procedures and didn't have heart attacks or require emergency surgery. CK-MB was routinely measured six to eight hours after angioplasty and the morning after angioplasty. About 17 percent of the patients (1,446) had CK-MB levels above normal after their procedures, and they were separated into two groups according to their CK-MB levels: one to five times the upper limit of normal or greater than five times the upper limit of normal.
Ellis and his associates found that no patient with CK-MB levels elevated less than five times normal died during the first week after catheterization. Most of the early deaths occurred during the first three to four months after the procedures. Patients whose CK-MB levels exceeded five times the upper limit had a mortality risk of 8.9 percent at four months. This was significantly greater than the 1.9 percent risk for patients who had CK-MB levels one to five times the upper limit, and the 1.2 percent for patients who had normal CK-MB levels.
The investigators compared patients who had CK-MB elevation after a catheter procedure and who died within four months to other groups of patients with and without elevated CK-MB. They identified several factors associated with an increased risk of early death: incomplete restoration of blood flow through a blocked vessel, heart failure, older age, impaired kidney function, and absence of statin therapy at discharge from the hospital. One of the comparisons also showed that the mortality risk was higher in patients who had elevated levels of C-reactive protein, a marker of inflammation.
Co-authors are Derek Chew, MBBS; Albert Chan, M.D.; Patrick L. Whitlow, M.D.; Jakob P. Schneider, R.N.; and Eric J. Topol, M.D.
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