La Clinical definition of Myocardial infarction involves the presence of acute myocardial injury detected by abnormal cardiac biomarkers in the context of evidence of acute myocardial ischemia (1).
Cardiac troponin I (cTnI) and T (cTnT) are components of the contractile apparatus of myocardial cells and are expressed almost exclusively in the heart. cTnI and cTnT are the preferred biomarkers for the assessment of myocardial damage and the high-sensitivity (hs)-cTn test is recommended for routine clinical use (1).
The presence of myocardial damage is defined when blood levels of cardiac troponin are increased above the upper reference limit (URL) of the 99th percentile (1)
Unfortunately, cardiac troponin concentrations are strongly influenced by age and the use of a uniform cutoff for the hs-cTnT test can lead to an overdiagnosis of myocardial infarction, in particular in elderly male subjects (2)
The relationship between age and cardiac troponin was observed for both troponin I and T doses, with the 99th percentile URL observed in the elderly for cardiac troponin I by twice the reference value and for troponin T by 3 times the value of the general normal population (1).
Cardiac troponin and age
The High-STEACS study (High-Sensitivity Troponin in the Evaluation of Patients with Suspected Acute Coronary Syndrome) is a randomized controlled trial evaluating the implementation of a high-sensitivity cardiac troponin I test in consecutive patients presenting with PS with suspected coronary syndrome (3)
46435 patients aged between 18 and 108 years.Compared to younger people the age population> 75 years old had the following characteristics: they were more often women; were less likely to present with chest pain or ischemia on the 12-lead ECG; had a higher prevalence of cardiovascular comorbidities, including ischemic heart disease, heart failure, diabetes, and chronic kidney disease. More than half had 2 or more chronic cardiovascular conditions compared to one-third of subjects aged 50 to 74 years (56% vs 32%, respectively, P<0.001).
Stratified patients by age<50, 50 to 74 and ≥75 years, the sensitivity of the threshold recommended by the guidelines was similar and 79.2%, 80.6% and 81.6%, respectively. Specificity decreased with advancing age from 98.3% to 95.5% and 82.6%. The use of age-adjusted 99th percentile thresholds improved specificity (91.3% vs. 82.6%) and positive predictive value (59.3% vs. 51.5%) for myocardial infarction in patients ≥75 years. This strategy failed to prevent the decrease in both parameters with increasing age and induced a marked reduction in sensitivity compared to the use of the threshold recommended by the guidelines (55.9 vs 81.6%).
Points of focus on clinical practice
- Cases of cardiac troponin elevation, in older patients presenting with suspected myocardial infarction, is motivated by acute myocardial damage, or chronic myocardial infarction or myocardial infarction type 2.
- The specificity and positive predictive value of high-sensitivity cardiac troponin to identify myocardial infarction decrease with age and are observed by applying sex-specific or age-adjusted 99th percentile diagnostic thresholds or a rule-in threshold in triage of patients with high probability of myocardial infarction.
- Serial tests of troponin showing an absolute change in its concentration increase discrimination for myocardial infarction in older patients.
- It is not advisable to interpret a single troponin measurement in elderly patients with suspected myocardial infarction.
- Serial measurements of cardiac troponin should be performed regularly, and absolute changes in troponin concentration should be evaluated to identify those older patients with elevated troponin concentrations who are more likely to have myocardial infarction.
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