Novel Biomarkers for Acute Myocardial Infarction: Is MicroRNA the New Kid on the Block?

Early detection of acute myocardial infarction (AMI)9 is crucial for deciding the course of treatment to preserve and prevent further damage to the myocardial tissue. Guidelines from the American College of Cardiology give the criteria for AMI as an increase or decrease in troponin with at least one value >99% percentile of a healthy population (with an imprecision of <10%) accompanied by either symptoms of ischemia or evidence of MI based on imaging or electrocardiography modalities. Over the last several years, creatine kinase MB testing has been replaced by newer generations of troponin assays. High-sensitivity assays are now considered the gold-standard marker for myocardial necrosis. Indeed, the improved analytical sensitivity of high-sensitivity troponin assays has lowered the threshold for myocardial injury, making it easier to detect baseline values in the picogram-per-milliliter range and thus expediting early diagnosis. The gains in diagnostic sensitivity have come at the cost of decreases in diagnostic specificity, however. A major challenge is that high-sensitivity assays quantify troponin in a greater proportion of healthy individuals. These assays also detect myocardial cell death associated with other pathophysiological conditions, such as cardiomyopathies, myocarditis, renal failure, congestive heart failure, and pulmonary embolism, and do not distinguish between mechanisms of tissue injury, thus limiting the ability to differentiate on the basis of MI severity [e.g., ST-segment elevation myocardial infarction (STEMI) vs. non-STEMI]. Consequently, the introduction of high-sensitivity troponin assays into clinical practice has caused confusion for physicians treating patients with acute chest pain. Therefore, the ideal biomarker to rule in and rule out AMI rapidly and reliably is still lacking. During the last several years, there has been a burgeoning interest in circulating microRNAs (miRNAs) as potential novel biomarkers for AMI. miRNA is a type of single-stranded, noncoding small ribonucleic acid (about 22 nucleotides in length) located within introns …