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Although troponin is a reliable cardiac biomarker in some contexts, it doesn't always indicate that a heart attack is happening.
This has been emphasized amid the COVID-19 pandemic, as researchers have identified noncardiac causes of elevated troponin levels in SARS-CoV-2 positive patients who experience multifactorial heart damage, as opposed to cardiac injury from myocardial infarction, or MI.1 Because of this, the American College of Cardiology in 2020 recommended troponin testing only if other clinical indicators, such as relevant symptoms and ECG evidence, were present in COVID-19 patients.2
However, the cardiac community had been questioning troponin's role in the definitive diagnosis of MI even before the pandemic.3 These perspectives are important to consider given the invasiveness of diagnostic pathways that will follow suspected occlusion, including coronary angiography. Getting the diagnosis right is imperative.
So, is elevated troponin still a reliable biomarker for acute cardiac injury—particularly in patients not infected with SARS-CoV-2? Evidence is divided: Laboratory values can support diagnostic decision-making, but not unilaterally as a single gold standard. Other tools, including ECG readings in conjunction with a full clinical workup, often provide more context.
Using ECG to Diagnose Acute Cardiac Injury
Assessment of ECG waveforms, particularly ST elevation and depression, can inform and differentiate MI from other cardiac diagnoses, including those caused by damage from SARS-CoV-2 infection. Indications of STEMI (ST-elevation MI) will generally include anterior, inferior, or posterior elevations in the ST segment. Other STEMI indicators may consist of a new right bundle branch block or a left bundle branch block.4
ST depression in leads recorded from the opposite side of the infarct site can also present in STEMI patients. This is known as reciprocal ST-segment depression, or RSTD, and has been reported historically in as many as 100% of inferior infarctions and 70% of anterior infarctions.5
RSTD may be particularly helpful in differentiating ST-elevated ischemic damage from other diagnoses that also present with ST elevations, including those that may occur from COVID-19, such as acute pericarditis. Using data from a pre-pandemic study in the Scandinavian Cardiovascular Journal,6 for example, the following indicators have helped to differentiate STEMI from nonischemic ST-elevations in the past:
- An RSTD value equaling or exceeding .025 mV in lead II (seen in 4 in 10 anterior STEMI patients but zero with nonischemic anterior elevations in the ST segment).
- An RSTD value equaling or exceeding .025 mV in lead I (seen in 8 in 10 STEMI patients with inferior ST elevations but zero with nonischemic diagnoses).
Given the correlations between RSTD and STEMI, reciprocal depression aids in ACS decision support, as it may be an important diagnostic indicator of ST elevations associated with myocardial infarction, versus those related to other causes of cardiac damage. Indicators of noncoronary damage may include depressions in the chest-lead PR or aVR ST segment.
To learn more about the power of the ECG in today's clinical landscape, browse our Diagnostic ECG Clinical Insights Center.
Care Pathways Following Diagnosis
One of the key benefits of ECG is that it can enable care teams to deploy next steps in triage and risk assessment of a potential cardiac event quickly—which may be particularly helpful given the operational strains that COVID-19 has placed on hospitals. Importantly, with STEMI, percutaneous coronary intervention is still the standard of care as long as other causes for ST-elevation have been ruled out.
Patients presenting with electrophysiology concerns—some of whom may also have elevated troponin—will likewise benefit from the rapid assessment of ECG to initiate care planning. This is critical since more than 40% of cardiac encounters are related to arrhythmias,7 and many may require urgent or emergent procedures such as VT ablation, pacemaker insertion, or cardioversion.
Pandemic or Not, ECG Is Vital
Instances of elevated troponin values from SARS-CoV-2 infection have added to a growing chorus of practitioners who doubt the unilateral application of this biomarker for MI diagnosis.
As troponin's reliability is questioned, other diagnostic tools, including ECG, stand to lead the way in fast and accurate bedside assessment. In patients with suspected COVID-19, The New England Journal of Medicine notes, "In most instances, and especially if a medication that affects the corrected QT (QTc) interval is considered, a baseline electrocardiogram should be obtained," but even non-infected patients may benefit from an ECG workup.8
Given the propensity of both coronary and noncoronary damage to cause ECG abnormalities, providers should familiarize themselves with waveform indicators and differentiators of injury, including ST elevations and depressions.
Ultimately, pandemic or not, ECG adds diagnostic value and context in uncertain circumstances surrounding cardiac events. Its ease of use, convenience, and fast insights make it a critical part of the cardiologist's toolbox.
1. Chapman AR, Bularga A, Mills NL. High-sensitivity cardiac troponin can be an ally in the fight against COVID-19. Circulation. Published online April 6, 2020. doi:10.1161/circulationaha.120.047008
2. American College of Cardiology. Troponin and BNP use in COVID-19. ACC.org. https://www.acc.org/latest-in-cardiology/articles/2020/03/18/15/25/troponin-and-bnp-use-in-covid19. Accessed February 2, 2022.
3. Adler C, Baldus S. Troponinerhöhung – benötigt jeder Patient eine Koronarangiographie? Medizinische Klinik - Intensivmedizin und Notfallmedizin. 2019;115(8):690-698. doi:10.1007/s00063-019-0593-4.
4. Healio. Top 5 MI ECG Patterns You Must Know. Healio.com. https://www.healio.com/cardiology/learn-the-heart/ecg-review/ecg-interpretation-tutorial/stemi-mi-ecg-pattern. Accessed February 2, 2022.
5. Camara EJN, Chandra N, Ouyang P, Gottlieb SH, Shapiro EP. Reciprocal ST change in acute myocardial infarction: Assessment by electrocardiography and echocardiography. Journal of the American College of Cardiology. 1983;2(2):251-257. doi:10.1016/s0735-1097(83)80160-0.
6. Lindow T. Electrocardiographic changes in the differentiation of ischemic and non-ischemic ST elevation. Scandinavian Cardiovascular Journal. https://www.tandfonline.com/doi/full/10.1080/14017431.2019.1705383. Accessed February 2, 2022.
7. Lakkireddy DR, Chung MK, Gopinathannair R, et al. Guidance for cardiac electrophysiology during the COVID-19 pandemic from the Heart Rhythm Society COVID-19 Task Force; Electrophysiology Section of the American College of Cardiology; and the Electrocardiography and Arrhythmias Committee of the Council on Clinical Cardiology, American Heart Association. Circulation. 2020;141(21). doi:10.1161/circulationaha.120.047063.
8. Gandhi RT, Lynch JB, del Rio C. Mild or moderate Covid-19. Solomon CG, ed. New England Journal of Medicine. 2020;383(18):1757-1766. doi:10.1056/nejmcp2009249.