NEW YORK (Reuters Health) – A new generation of sensitive assays for measuring cardiac troponin I could enhance the diagnostic accuracy for acute myocardial infarction (MI), even early after chest pain onset.

These findings, from two prospective, multicenter studies published in the New England Journal of Medicine for August 27, augur well for earlier, more effective care of patients with acute coronary syndrome, particularly those without ST-segment deviation on ECG, the authors maintain.

Standard cardiac troponin assays require repeated blood sampling over 6 to 12 hours, due both to the assays’ low sensitivity and to delayed increases in circulating troponin after MI, Dr. Christian Mueller, from University Hospital Basel, Switzerland and associates explain. Delayed diagnosis contributes to increased complications and overcrowded emergency rooms.

In the Advantageous Predictors of Acute Coronary Syndromes Evaluation study, Dr. Mueller and his colleagues measured cardiac troponin levels in emergency department patients using four sensitive assays (Abbott-Architect Troponin I, Roche High-Sensitive Troponin T, Roche Troponin I, and Siemens Troponin I Ultra) along with a standard assay (Roche Troponin T).

Among 718 patients who presented with symptoms of MI from April 2006 through April 2008 (median age 64 years), the final diagnosis was acute MI in 17%, unstable angina in 16%, cardiac symptoms from causes other than coronary artery disease in 13%, noncardiac causes in 46%, and symptoms of unknown origin in 8%.

When areas under the receiver-operating characteristic curves (AUC) were compared, diagnostic accuracy for acute MI was significantly higher with the four sensitive assays (AUCs 0.94-0.96) than with the standard assay (0.90).

The superiority of the sensitive assays was most pronounced in patients presenting within 3 hours of pain onset, with AUCs of 0.92 to 0.94 for the sensitive assays versus 0.76 for the standard assay. The four sensitive assays were also significantly more accurate than the MB fraction of creatine kinase and myoglobin.

Diagnostic performance of the four sensitive assays was similar for ST and non-ST segment-elevation acute MI, for both genders, for patients older and younger than 70 years of age, and for patients with normal or reduced renal function.

Dr. Mueller’s team cautions, however, that sensitive cardiac troponin assays for early diagnosis of acute MI “should be used only in conjunction with a detailed clinical assessment” to rule out other conditions.

In a similar study, Dr. Stefan Blankenberg at the Johannes Gutenberg University in Mainz, Germany, and co-investigators compared the Siemens Troponin I Ultra with conventional troponin assays in 1818 patients, 413 (22.7%) of whom were diagnosed with acute MI.

Again, the diagnostic accuracy was highest with the sensitive assay (AUC 0.96 vs 0.85). Using a cutoff value of 0.04 ng/mL on admission, the clinical sensitivity at presentation was 91%, and specificity was 90%.

“Future studies,” Dr. Blankenberg’s team concludes, “will be needed to determine whether the early diagnosis of myocardial infarction facilitates rapid use of invasive strategies and thus improves the outcome in patients with myocardial infarction.”

Reference:
N Engl J Med 2009;361:858-867,868-877.