Avoiding STEMI and NSTEMI Misdiagnoses with Fast, Accurate ECG Interpretation

Emergency providers roll a patient on a gurney through the ED.

In the case of a cardiac event, every minute that passes is precious, and any amount of time that's wasted—whether due to a delayed diagnostic workup or faulty ECG interpretation—can risk lasting damage to muscles and organs.

Yet many cardiologists spend those initial minutes pursuing diagnoses that end up being wrong, according to a cohort study conducted by the Myocardial Ischemia National Audit Project using data from more than half a million patients. In the Editor's Choice study, published in the European Heart Journal: Acute Cardiovascular Care, investigators found that nearly a third of all patients with acute myocardial infarction had their diagnoses changed during their care.1

The changes included shifts from non-ST-elevation myocardial infarction (NSTEMI) to STEMI and vice versa, as well as adjustments to STEMI and NSTEMI from angina of unknown causes. Due to those initial NSTEMI and STEMI misdiagnoses, patients were less likely to receive guideline-based care and experienced elevated mortality rates. According to the study's authors, if STEMI and NSTEMI patients had received correct diagnoses from the outset, 251 lives could have been saved annually.1

The Importance of Taking Faster ECGs

It is not difficult to imagine how prompt use of ECG could have affected these numbers, yet only 24.3% and 21.5% of patients received a prehospital ECG for diagnoses that turned out to be STEMI and NSTEMI, respectively.1 These rates are concerning, given that suspected ACS in any setting—hospital or not—should be evaluated within ten minutes of first medical contact with a 12-lead ECG, as the U.S. chest pain guidelines recommend.2

That ten-minute mark matters due to the urgency of the intervention windows. American College of Cardiology/American Heart Association (ACC/AHA) guidelines dictate that patients with STEMI should receive treatment via thrombolytic or emergency cath within thirty and ninety minutes, respectively.3

Still, some settings facilitate timely diagnostics better than others. Notably, emergency departments (EDs) commonly struggle with obtaining prompt ECG readings, given all the registration, triage, and other administrative matters involved in an emergency room check-in. One study from the Journal of the American Heart Association found that nearly 13% of STEMI patients did not receive an ECG within fifteen minutes, and one case even involved an eighty-minute wait.4

Researchers attribute these variances to complexities in ECG screening criteria and have called for more widespread and actionable recommendations for ECG evaluation of suspected acute coronary syndrome (ACS). In the meantime, physicians in any setting should remember the recommendations in the chest pain guidelines: if a patient experiences acute chest pain, run the ECG to check for STEMI within ten minutes of arrival. It's fast, easy, and widely accessible at the point-of-care, so there's no reason not to do so.

It's important to note that respiratory distress can affect ECG quality, with increased breathing rate and retractions potentially creating artifacts and sweating possibly causing the electrodes to slide or fall off. To get a high-quality recording, practice good skin preparation, take care to place electrodes in the proper locations, and check filter settings. Also, aim to get the patient to remain as still as possible and pay attention to the signal quality indicator if your device has one.

To learn more about ECG Matters, watch this webinar presentation by Dr. Anthony Kashou, "The ECG: What Is Normal?"

Ensuring Accurate ECG Interpretation

Even with prompt ECGs, providers need to interpret the results correctly. Ensuring proper and adequate training for all practitioners on the waveforms most indicative of NSTEMI and STEMI can help significantly.

Many ECG platforms now feature computerized components that can support diagnostic decision-making at rates on par with, or even exceeding, human electrocardiographer capabilities. One such program, GE Healthcare's Marquette 12SL, was found to have an adequate predictive value in STEMI diagnoses, according to a study in the Canadian Journal of Emergency Medicine.5 By employing computer-assisted ECG interpretation, clinicians could minimize analysis time by up to 28%, as a study in the Journal of the American College of Cardiology found, which would better position them to meet that critical ten-minute window in high-volume times, such as during the COVID-19 pandemic.6

Understanding the Full Picture

Though advanced solutions can augment human capabilities, it's important to underscore that they cannot replace them. An ACS diagnosis should factor in ECG findings, but it should not entirely depend on them, as not all cases of MI will present with an abnormal ECG. One study in Cureus, for example, showed that in a group of patients who presented with symptoms suggestive of ACS but had unremarkable initial ECGs, 22.8% ultimately received a diagnosis of NSTEMI.7

Diagnoses should be informed by technologies and other clinical indications, including personal history, family history, presentation of symptoms, access to previous ECG readings, and—with certain caveats—the results of laboratory testing advised by the care team, such as high-sensitivity troponin testing.

Together, these tools can support a broader picture of underlying mechanisms behind cardiac events and inform correct diagnoses the first time around. After all, every minute risks precious blood flow and tissue viability, so time is not just muscle; it's life. We cannot waste one bit of it.


1. Wu J, Gale CP, West RM, et al. Editor's choice – impact of initial hospital diagnosis on mortality for acute myocardial infarction: a national cohort study. European Heart Journal: Acute Cardiovascular Care. March 2018; 7(2): 139-148. https://academic.oup.com/ehjacc/article/7/2/139/5932651

2. Gulati M, Levy PD Mukherjee D, et al. 2021 AHA/ACC/ASE/CHEST/SAEM/SCCT/SCMR guideline for the evaluation and diagnosis of chest pain: a report of the American College of Cardiology/American Heart Association joint committee on clinical practice guidelines. Journal of the American College of Cardiology. November 2021; 78(22): e187-e285. https://www.jacc.org/doi/10.1016/j.jacc.2021.07.053

3. O'Gara PT, Kushner FG, Ascheim DD, et al. 2013 ACCF/AHA guideline for the management of ST-elevation myocardial infarction: a report of the American College of Cardiology Foundation/American Heart Association task force on practice guidelines. Journal of the American College of Cardiology. January 2013; 61(4): e78-e140. https://www.jacc.org/doi/10.1016/j.jacc.2012.11.019

4. Yiadom MYAB, Baugh CW, McWade CM, et al. Performance of emergency department screening criteria for an early ECG to identify ST-segment elevation myocardial infarction. Journal of the American Heart Association. February 2017; 6(3): e003528. https://www.ahajournals.org/doi/full/10.1161/jaha.116.003528

5. De Champlain F, Boothroyd LJ, Vadeboncoeur A, et al. Computerized interpretation of the prehospital electrocardiogram: predictive value for ST segment elevation myocardial infarction and impact on on-scene time. Canadian Journal of Emergency Medicine. March 2014; 16(2): 94-105. https://www.cambridge.org/core/journals/canadian-journal-of-emergency-medicine/article/computerized-interpretation-of-the-prehospital-electrocardiogram-predictive-value-for-st-segment-elevation-myocardial-infarction-and-impact-on-onscene-time/3343435B5954B6CB87AA383F30525B50

6. Schläpfer J, Wellens HJ. Computer-interpreted electrocardiograms: benefits and limitations. Journal of the American College of Cardiology. August 2017; 70(9): 1183-1192. https://www.jacc.org/doi/abs/10.1016/j.jacc.2017.07.723

7. Khan R, Akhter J, Munir U, et al. Frequency of non-ST segment elevation myocardial infarction (NSTEMI) in acute coronary syndrome with normal electrocardiogram (ECG): insights from a cardiology hospital in Pakistan. Cureus. June 2020; 12(6): e8758. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7377671/