Highlight
The diagnostic utility of Cardiac Myosin-Binding Protein C (cMyC) has emerged as a significant advancement in the early detection of non-ST-segment elevation myocardial infarction (NSTEMI). Key highlights from this comprehensive analysis include:
1. cMyC demonstrated superior diagnostic discrimination compared to high-sensitivity cardiac troponin T (hs-cTnT), particularly in patients presenting within three hours of chest pain onset.
2. A novel dual-biomarker strategy, combining cMyC with hs-cTn, increased emergency department (ED) triage efficacy from 26.8% to 60.0% using a single blood draw.
3. The accelerated rule-out process did not compromise patient safety, with comparable 30-day and 5-year cardiovascular outcomes between the dual-biomarker and standard-of-care approaches.
Background: The Challenge of Early NSTEMI Diagnosis
For decades, cardiac troponins (cTn) have served as the cornerstone of myocardial infarction diagnosis. The advent of high-sensitivity assays (hs-cTnT and hs-cTnI) significantly improved sensitivity, allowing for earlier detection of myocardial injury. However, even with high-sensitivity assays, a “troponin-blind” window often persists in the first hours following symptom onset due to the time required for troponin levels to exceed the 99th percentile of the upper reference limit.
In the context of overcrowded emergency departments, the need for rapid, safe, and efficient triage is paramount. Current European Society of Cardiology (ESC) guidelines recommend 0/1-hour or 0/2-hour algorithms, which require serial blood draws. A single blood draw strategy that can reliably rule out NSTEMI at presentation would represent a major leap in operational efficiency and patient care.
The Biological Rationale for cMyC
Cardiac myosin-binding protein C (cMyC) is a cardiac-specific protein located in the thick filament of the sarcomere. It is significantly more abundant than cardiac troponin and, crucially, exhibits faster release kinetics following myocardial injury. Unlike troponin, which is partly bound to the structural elements of the cell, cMyC is rapidly released into the circulation upon loss of cell membrane integrity. This biological profile makes cMyC an ideal candidate for improving diagnostic accuracy in the hyper-acute phase of NSTEMI.
Study Design and Methodology
This study was a secondary analysis derived from the Advantageous Predictors of Acute Coronary Syndromes Evaluation (APACE) study, an international, prospective, multicenter investigation. The cohort included 4,735 adult patients presenting to the ED with symptoms suggestive of NSTEMI, such as acute chest pain or dyspnea.
Concentrations of cMyC (measured with a novel prototype automated immunoassay), hs-cTnT, and hs-cTnI were obtained at the time of ED presentation. The final diagnosis for each patient was centrally adjudicated by two independent cardiologists who were blinded to the cMyC results. The primary diagnostic endpoint was index NSTEMI, while the prognostic endpoints included cardiovascular death or MI at 30 days, 1 year, and 5 years. The findings were further validated in an independent international cohort to ensure generalizability.
Key Findings
The results of the study provide compelling evidence for the incremental value of cMyC in clinical practice.
Diagnostic Discrimination
cMyC exhibited a higher area under the curve (AUC) for NSTEMI discrimination at presentation (0.943; 95% CI: 0.936-0.95) compared to hs-cTnT (0.936; 95% CI: 0.929-0.944; P = 0.008). This advantage was most pronounced in patients presenting early—specifically those with chest pain onset within three hours. In this subset, the AUC for cMyC was 0.939, significantly outperforming hs-cTnT’s AUC of 0.921 (P < 0.001).
Triage Efficacy and Safety
The most striking finding was the impact on triage efficacy. By employing a single blood draw dual-biomarker strategy (combining hs-cTn and cMyC), clinicians could successfully triage 60.0% of patients to either “rule-out” or “rule-in” status immediately upon presentation. This is a massive improvement over the 26.8% triage efficacy achieved when using hs-cTnT alone.
Importantly, this increased speed did not come at the cost of safety. The negative predictive value (NPV) and sensitivity for ruling out NSTEMI remained high, meeting the rigorous safety standards required for clinical implementation. Even though the dual-biomarker strategy identified up to three times more patients for immediate rule-out, the incidence of major adverse cardiovascular events (MACE) remained low and comparable to the traditional ESC-endorsed strategies.
Long-term Prognostic Value
The study followed patients for up to five years, providing a robust look at long-term outcomes. The cumulative incidences of cardiovascular death or MI at 30 days, 1 year, and 5 years were similar between patients ruled out by the cMyC-inclusive strategy and those ruled out by standard high-sensitivity troponin protocols. This confirms that the rapid rule-out enabled by cMyC is prognostically sound.
Expert Commentary and Clinical Interpretation
The ability to safely rule out a myocardial infarction with a single blood test at the point of presentation is a “holy grail” in emergency medicine. The data from Lopez-Ayala et al. suggest that cMyC brings us closer to this reality. By leveraging the faster release kinetics of this sarcomeric protein, clinicians can identify low-risk patients much earlier than previously possible.
However, some considerations remain. While the automated immunoassay used in this study is a prototype, its transition to widespread clinical availability will be necessary before these findings can change global practice. Additionally, while the dual-biomarker strategy is highly effective, it does not replace the need for clinical judgment and the consideration of the patient’s overall risk profile, including ECG findings and physical examination.
Mechanistically, the superior performance of cMyC in the early hours of symptom onset reinforces the importance of understanding the molecular release of cardiac proteins. As our assays become more refined, the focus is shifting from simply “detecting” injury to “timing” and “quantifying” it with extreme precision.
Conclusion
Cardiac myosin-binding protein C provides significant incremental value to high-sensitivity cardiac troponins in the acute setting. By improving diagnostic discrimination—especially in the early window of symptom onset—and doubling the efficacy of ED triage, cMyC has the potential to transform the management of suspected NSTEMI. The single blood draw dual-biomarker strategy offers a simplified, rapid, and safe alternative to current serial testing protocols, promising to alleviate ED overcrowding and improve the patient experience.
Funding and ClinicalTrials.gov
The APACE study was supported by the Swiss National Science Foundation, the Swiss Heart Foundation, and various research grants from industry partners including Roche and Abbott. The trial is registered at ClinicalTrials.gov (NCT00470587).
References
Lopez-Ayala P, Boeddinghaus J, Koechlin L, et al. Incremental Value of Cardiac Myosin-Binding Protein C for the Early Diagnosis of Acute Myocardial Infarction. J Am Coll Cardiol. 2025 Dec 23;86(25):2616-2632. doi: 10.1016/j.jacc.2025.09.008. Epub 2025 Nov 12. PMID: 41222525.
