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Before COVID-19, using troponin was a debatable "gold standard" for detecting acute coronary syndrome (ACS), specifically myocardial infarction, but this may no longer be the best diagnostic strategy.
As a recent Circulation paper opines, the idea that this method ever was a panacea is a fallacy: Troponin—or any other biomarker, for that matter—cannot single-handedly identify a blocked artery. That kind of diagnosis is informed by the lab, but it's confirmed by waveforms and imaging, including ACS-related ECG findings.
Cardiologists have long argued that fact, but now with the known cardiac effects of COVID-19, there is more empirical evidence to make the case that troponin isn't as effective of a barometer for ACS as was once believed.
Diagnostic Challenges of Troponin Testing
SARS-CoV-2 invades the heart muscle, contributes to cellular rupture, and leads to elevated troponin in as many as 27.8% of infected patients, according to a white paper published in the Journal of the American Heart Association. Notably, in one early study preprinted in medRxiv, autopsies of COVID-19 patients revealed scattered areas due to cellular rupture, as opposed to isolated damage indicative of ischemic myocardial injury.
Indeed, patients with elevated troponin may have underlying ischemic damage, but they could also be experiencing cardiac issues that can be attributed solely to the virus or some other factor, such as chronic heart failure. This difference is important because while the latter may raise the risk for cardiac events in the future, as the Circulation paper notes, it doesn't require immediate intervention, such as coronary angiography.
This complicates the cardiovascular picture and shifts diagnostic confidence from the lab back to the bedside. By examining known ACS ECG findings, providers can more accurately diagnose occlusions and advance the correct care pathways as quickly as possible.
ACS-Related ECG Findings That Support Diagnosis
In combination with a symptom assessment, a multitude of ECG abnormalities can help inform diagnoses of STEMI and non-ST elevation ACS (such as unstable angina and non-ST elevation MI, or NSTEMI).
- STEMI: As illustrated in a Healio chart guide, ECG abnormalities indicative of STEMI can present through anterior, inferior, or posterior ST segment elevations, as well as MI with a right bundle branch block (as indicated by an RSR' on V1) or a new left bundle branch block (marked by a QS or rS on V1 and V2 with ST elevation).
- Unstable Angina or NSTEMI: In the absence of ST elevation, NSTEMI and unstable angina have typically relied on troponin testing: Troponin historically indicated NSTEMI, while a lack of it marked unstable angina. Still, there are other ECG findings that can inform diagnosis. Healio points out that both can include ST depression (sloping down or laterally) or T-wave inversions (often symmetrical).
Comparisons to prior ECGs and awareness of serial STT changes are also critical to making informed diagnoses.
One Tool in a Broad Toolkit
Some COVID-19 patients may have elevated levels of troponin due to preexisting cardiac damage, while for others, those biomarkers may link back to the virus' rampaging effects on the body. In any case, the role of ECG as a first-line solution is reaffirmed for ACS.
Even so, waveforms are just one tool within a broad diagnostic toolkit that includes symptom assessments, medical history, and (still debatably) also troponin, as the Circulation authors argue. While high-sensitivity biomarker testing may be less reliable in singling out ACS, it may still have utility in assessing the extent of myocardial injuries and organ dysfunction caused by COVID-19.
Knowing this could help clinicians more quickly deploy treatments, improve outcomes, make informed triage decisions for critical care, and fill in the many knowledge gaps around the virus.
However, given the nonspecific nature of elevated troponin levels among COVID-19 patients, the American College of Cardiology (ACC) has recommended against more widespread testing for troponin. As an ACC guidance document that partly prompted the subsequent Circulation opinion advises, biomarker testing should only be indicated for those with suspected acute MI.
Regardless of the potential utility, indication, and appropriateness of a troponin test, ECG still provides accurate insights at the point-of-care. In an era when bandwidth and capacity are stretched, having that kind of fast and reliable decision support can make all the difference.