Predictive value of cardiac troponin-I compared to creatine kinase-myocardial band for the assessment of infarct size as measured by cardiac magnetic resonance.

Background: The estimation of infarct size by biochemical myocardial necrosis markers is used in current clinical practice, rather than the more expensive and not always available imaging techniques. However, for this purpose, the peak value of serum biomarkers can overestimate the necrotic area, especially after reperfusion.

Objective: We investigated whether late release cardiac troponin I (cTnI) values could predict more precisely infarct volume measured by delayed-enhancement cardiac magnetic resonance (DE-CMR) in patients with acute myocardial infarction [ST-elevation myocardial infarction (STEMI) and non-STEMI (NSTEMI)] independently of reperfusion (spontaneous and provoked).

Methods: Sixty patients with a first acute myocardial infarction (55 STEMI and five NSTEMI) and normal function were enrolled. Among STEMI patients, 52 underwent reperfusion. cTnI and creatine kinase-myocardial band were assessed at admission and at 6, 12, 24, 48, 72 and 96 h (+/-1 h) from symptom onset. DE-CMR (Siemens Avanto 1.5T) was performed before discharge (4 +/- 2 days). Infarct size was determined by manual delineation of the areas of delayed enhancement. Infarct volume was calculated as the sum of each slice of infarct size area multiplied by thickness.

Results: Peak cTnI was 55 +/- 59 ng/ml (range 0.3-347). The area under the curve of cTnI was 1916 +/- 2224 ng/ml. The volume of infarcted myocardium assessed by DE-CMR was 27 +/- 25 ml (range 0-134). The single value of cTnI at 72 h after symptom onset provided the most accurate estimation of predischarge infarct volume (r = 0.84, 95% confidence interval 0.75-0.91) and was significantly more accurate than creatine kinase-myocardial band value assessed at any time during the same period (r = 0.42, 95% confidence interval 0.19-0.62; P < 0.002).

Conclusion: In patients with a first acute myocardial infarction, cTnI value assessed at 72 h from symptom onset shows the best correlation with predischarge infarct volume as assessed by DE-CMR and is superior to cTnI and creatine kinase-myocardial band peak and total values.