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Creatine Kinase-MB Wins at Predicting Cardiac Outcomes

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Myocardium specific creatine kinase levels appear to provide a better prognosis of long-term outcomes for elective heart surgery patients than do measures of troponin, according to a prospective study.

The study of more than 200 elective cardiac surgery patients followed for a mean of 7.6 years found that the incidence of cardiac events was 41.2% among those with high creatine kinase-MB levels after surgery compared with 21.8% of controls (P=0.004) — and the event incidence was 33.1% for patients with high cardiac troponin tests versus 21.8% of controls (P=0.075), researchers reported online in the American Journal of Cardiology.

At the same time, the incidence of cardiac events was 27% among those patients who had high cardiac troponin I post-surgery, compared with 34.6% of controls (P=0.237), according to Kjell Vikenes, MD, PhD, consultant in cardiology at Haukeland University Hospital, Bergen, Norway, and colleagues.

“To our knowledge, the present study is the first to report on the long-term prognostic value comparing cardiac troponin, cardiac troponin I and creatine kinase-MB mass in low-risk, stable patients in the same study population,” wrote Vikenes and co-authors.

For their study, Vikenes and colleagues followed 204 consecutive patients who underwent elective cardiac surgery — either coronary artery bypass grafting and/or valve surgery — for a mean of 92 months.

All the patients in the study had stable cardiac symptoms for at least one month prior to treatment.

The mean age of the study patients was 70.9 years and 77% were men. Around 78% had elective coronary artery bypass graft procedures.

About 76% of the study patients had high cholesterol levels and 28% were hypertensive. Some 57% had ever smoked and around 24% were current smokers.

All of the patients had creatine kinase-MB, cardiac troponin, and cardiac troponin I measured twice within eight hours after surgery, and then daily for three days post-surgery.

Patients were judged to have high levels of creatine kinase-MB or troponins if their test results were ≥5 times the reference values.

The endpoint event was the composite of all-cause mortality, readmission for acute coronary syndromes, and target vessel revascularization.

“Creatine kinase-MB was superior to the cardiac troponins in predicting long-term event-free survival after elective cardiac surgery in low-risk patients with stable symptoms undergoing coronary artery bypass grafting and/or valve surgery,” Vikenes and colleagues reported in their paper.

“The recent guidelines for diagnosing perioperative infarcts have advocated the use of similar thresholds for creatine kinase-MB and the cardiac troponins,” the researchers wrote. “However, few previous data are available comparing these biomarkers after cardiac surgery, and it is not clear whether postoperative elevations of the troponins can be treated the same as elevations of creatine kinase-MB.”

“Creatine-kinase-MB might be a more robust biomarker in this setting, because its release might to a larger degree represent cell death compared to cardiac troponin and, in particular, compared to cardiac troponin I, which might leak more easily through a damaged cell membrane,” Vikenes and his group suggested.

“Possibly, it is the degree of micronecrosis that predicts subsequent adverse events during follow-up in these stable patients,” they added.

It could be argued that higher thresholds of the troponins would have performed better, the researchers suggested.

“For that reason, we did compare the upper and the lower quartiles, as well as the upper and lower tertiles. The upper tertile reflected somewhat greater thresholds of the troponins but was quite similar to the five-fold threshold of creatine kinase-MB,” they wrote.

“Only creatine kinase-MB demonstrated a significant difference between the upper and lower tertiles, further supporting the better prognostic value of creatine kinase-MB compared to the troponins in low-risk patients undergoing routine heart surgery,” the authors concluded.

Source: MedPage Today