Sandoval, Yader

Abstract Background Type 2 myocardial infarction (T2MI) is frequently encountered in clinical practice and associated with adverse outcomes. Content T2MI occurs most frequently due to noncoronary etiologies that alter myocardial oxygen supply and/or demand. The diagnosis of T2MI is often confused with acute nonischemic myocardial injury, in part because of difficulties in delineating the nature of symptoms and misunderstandings about disease categorization. The use of objective features of myocardial ischemia using electrocardiographic (ECG) or imaging abnormalities may facilitate more precise T2MI diagnosis. High-sensitivity cardiac troponin (hs-cTn) assays allow rapid MI diagnosis and risk stratification, yet neither maximum nor delta values facilitate differentiation of T2MI from T1MI. Several investigational biomarkers have been evaluated for T2MI, but none have robust data. There is interest in evaluating risk profiles among patients with T2MI. Clinically, the magnitude of maximum and delta cTn values as well as the presence and magnitude of ischemia on ECG or imaging is used to indicate disease severity. Scoring systems such as GRACE, TIMI, and TARRACO have been evaluated, but all have limited to modest performance, with substantial variation in time intervals used for risk-assessment and endpoints used. Summary The diagnosis of T2MI requires biomarker evidence of acute myocardial injury and clear clinical evidence of acute myocardial ischemia without atherothrombosis. T2MIs are most often caused by noncoronary etiologies that alter myocardial oxygen supply and/or demand. They are increasingly encountered in clinical practice and associated with poor short- and long-term outcomes. Clinicians require novel biomarker or imaging approaches to facilitate diagnosis and risk-stratification.

Abstract Background Concerns exist regarding how the 99th percentile upper reference limit (URL) of cardiac troponin (cTn) is determined and whether it should be derived from normal healthy individuals. Content The 99th percentile URL of cTn is an important criterion to standardize the diagnosis of myocardial infarction (MI) for clinical, research, and regulatory purposes. Statistical heterogeneity in its calculation exists but recommendations have been proposed. Some negativity has resulted from the fact that with some high-sensitivity (hs) cTn assays, a greater number of increases above the 99th percentile are observed when transitioning from a contemporary assay. Increases reflect acute or chronic myocardial injury and provide valuable diagnostic and prognostic information. The etiology of increases can sometimes be difficult to determine, making a specific treatment approach challenging. For those reasons, some advocate higher cutoff concentrations. This approach can contribute to missed diagnoses. Contrary to claims, neither clinical or laboratory guidelines have shifted away from the 99th percentile. To support the diagnosis of acute MI, the 99th percentile URL remains the best-established approach given the absence of cTn assay standardization. Importantly, risk stratification algorithms using hs-cTn assays predict the possibility of MI diagnoses established using the 99th percentile. Summary The 99th percentile of cTn remains the best-established criterion for the diagnosis of acute MI. While not perfect, it is analytically and clinically evidence-based. Until there are robust data to suggest some other approach, staying with the 99th percentile, a threshold that has served the field well for the past 20 years, appears prudent.

Background: Type 2 myocardial infarction (T2MI) occurs because of an acute imbalance in myocardial oxygen supply and demand in the absence of atherothrombosis. Despite being frequently encountered in clinical practice, the population-based incidence and trends remain unknown, and the long-term outcomes are incompletely characterized. Methods: We prospectively recruited residents of Olmsted County, Minnesota, who experienced an event associated with a cardiac troponin T >99th percentile of a normal reference population (≥0.01 ng/mL) between January 1, 2003, and December 31, 2012. Events were retrospectively classified into type 1 myocardial infarction (T1MI, atherothombotic event), T2MI, or myocardial injury (troponin rise not meeting criteria for myocardial infarction [MI]) using the universal definition. Outcomes were long-term all-cause and cardiovascular mortality and recurrent MI. T2MI was further subclassified by the inciting event for supply/demand mismatch. Results: A total of 5460 patients had at least one cardiac troponin T ≥0.01 ng/mL; 1365 of these patients were classified as index T1MI (age, 68.5±14.8 years; 63% male) and 1054 were classified as T2MI (age, 73.7±15.8 years; 46% male). The annual incidence of T1MI decreased markedly from 202 to 84 per 100 000 persons between 2003 and 2012 ( P <0.001), whereas the incidence of T2MI declined from 130 to 78 per 100 000 persons ( P =0.02). In comparison with patients with T1MI, patients with T2MI had higher long-term all-cause mortality after adjustment for age and sex, driven by early and noncardiovascular death. Rates of cardiovascular death were similar after either type of MI (hazard ratio, 0.8 [95% CI, 0.7–1.0], P =0.11). Subclassification of T2MI by cause demonstrated a more favorable prognosis when the principal provoking mechanism was arrhythmia, in comparison with postoperative status, hypotension, anemia, and hypoxia. After index T2MI, the most common MI during follow-up was a recurrent T2MI, whereas the occurrence of a new T1MI was relatively rare (estimated rates at 5 years, 9.7% and 1.7%). Conclusions: There has been an evolution in the type of MI occurring in the community over a decade, with the incidence of T2MI now being similar to T1MI. Mortality after T2MI is higher and driven by early and noncardiovascular death. The provoking mechanism of supply/demand mismatch affects long-term survival. These findings underscore the healthcare burden of T2MI and provide benchmarks for clinical trial design.

Abstract Background How to select healthy reference subjects in deriving 99th percentiles for cardiac troponin assays still needs to be clarified. To assist with global implementation of high sensitivity (hs)-cardiac troponin (cTn) I and hs-cTnT assays in clinical practice, we determined overall and sex-specific 99th percentiles in 9 hs-cTnI and 3 hs-cTnT assays using a universal sample bank (USB). Methods The Universal Sample Bank (USB) comprised healthy subjects, 426 men and 417 women, screened using a health questionnaire. Hemoglobin A1c (&gt;URL 6.5%), NT-proBNP (&gt;URL 125 ng/L) and eGFR (&lt;60 mL/min), were used as surrogate biomarker exclusion criteria along with statin use. 99th percentiles were determined by nonparametric, Harrell--Davis bootstrap, and robust methods. Results Subjects were ages 19 to 91 years, Caucasian 58%, African American 27%, Pacific Islander/Asian 11%, other 4%, Hispanic 8%, and non-Hispanic 92%. The overall and sex-specific 99th percentiles for all assays, before and after exclusions (n = 694), were influenced by the statistical method used, with substantial differences noted between and within both hs-cTnI and hs-cTnT assays. Men had higher 99th percentiles (ng/L) than women. The Roche cTnT and Beckman and Abbott cTnI assays (after exclusions) did not measure cTn values at ≥ the limit of detection in ≥50% women. Conclusions Our findings have important clinical implications in that sex-specific 99th percentiles varied according to the statistical method and hs-cTn assay used, not all assays provided a high enough percentage of measurable concentrations in women to qualify as a hs-assay, and the surrogate exclusion criteria used to define normality tended to lower the 99th percentiles.