The diagnosis of ST-Elevation Myocardial Infarction (STEMI) is a time-sensitive clinical challenge with critical implications for morbidity and mortality1. However, identifying a true STEMI based solely on ECG changes is not always straightforward, as a number of other conditions, collectively termed STEMI mimics, can produce ST-segment elevations without underlying myocardial infarction2. Misinterpreting these mimics as true STEMI can lead to unnecessary cath lab activations, resulting in invasive procedures that carry inherent risks3.
While the ECG is a crucial rule-in test for STEMI diagnosis, it is not a reliable rule-out test. This means that while significant ST-elevation on an ECG strongly suggests myocardial infarction and warrants urgent action, the absence of these findings does not necessarily exclude acute coronary syndromes (ACS)4. It is critical to correlate ECG findings with the patient’s clinical presentation, symptoms, and additional diagnostic markers, such as troponin levels, to ensure an accurate diagnosis5.
In this article, we explore the most common STEMI mimics, their clinical and ECG characteristics, and the role of advanced diagnostic tools, including AI-driven solutions, in aiding accurate and timely diagnosis.
What Are STEMI Mimics?
STEMI mimics are conditions that cause ST-segment elevation on an ECG but are not due to acute coronary occlusion. These may be cardiac or non-cardiac in origin, and each presents a unique challenge to the clinician2.
Unnecessary cath lab activations due to STEMI mimics are relatively common, with studies estimating that approximately 10-36% of patients presenting with ST-segment elevation on ECGs do not have an acute coronary occlusion upon angiography6,7. Misdiagnosing these conditions as STEMI can lead to inappropriate interventions, exposing the patient to potential complications of invasive procedures, such as contrast-induced nephropathy, radiation exposure, bleeding, and others6,7.
The ability to distinguish these mimics is essential for patient safety and resource optimization in busy emergency settings7.
Common STEMI Mimics and Their Diagnostic Pitfalls
Some of the most notable conditions mimicking STEMI include subarachnoid hemorrhage, Left Bundle Branch Block (LBBB), pericarditis, spontaneous coronary artery dissection (SCAD), hyperkalemia, ventricular paced rhythm, Brugada syndrome, hypothermia, Prinzmetal’s/Variant angina, pulmonary embolism, Takotsubo cardiomyopathy, ventricular aneurysm, left ventricular hypertrophy, early repolarization, and thoracic aortic dissection. Each of these conditions can present with ECG changes that resemble STEMI, yet they require different treatment approaches, underscoring the importance of careful clinical evaluation8.
Below, we examine several STEMI mimics, focusing on their ECG characteristics, the mechanisms behind their resemblance to STEMI, and some of the key clinical clues that help differentiate them.
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Pericarditis
Pericarditis is an inflammatory condition affecting the pericardium, which can be of infectious (often viral) or non-infectious origin, including autoimmune diseases, cancer, post-cardiac injury syndromes, post-myocardial infarction syndromes, Dressler’s syndrome and others9,11.
ECG Features of Pericarditis
- Diffuse ST-segment elevation across multiple leads, typically concave (upward-sloping).
- PR-segment depression in leads with ST-elevation, particularly in the inferior leads.
- Absence of reciprocal changes typically seen in STEMI10.
Clinical Clues
- Sharp, pleuritic chest pain that worsens with inspiration or lying down and improves when sitting upright.
- Pericardial friction rub on auscultation.
- Absence of elevated troponin levels, or mild elevation if myocarditis is also present10.
How Pericarditis Mimics STEMI
Pericarditis can lead to localized ST elevation, but unlike STEMI, it typically lacks reciprocal ST depression, except in leads aVR and V1. Both conditions can produce concave ST elevation, but only STEMI typically results in convex or horizontal ST elevation. Additionally, if the ST elevation is greater in lead III than in lead II, this is a strong indicator of STEMI. PR-segment depression is mostly associated with viral pericarditis and tends to be a transient, early feature, lasting only a few hours12.
Left Ventricular Hypertrophy (LVH)
LVH results from chronic pressure overload, often due to long-standing hypertension or aortic stenosis. The hypertrophied myocardium alters the electrical conduction patterns, leading to ST-segment abnormalities on the ECG13.
ECG Features of Left Ventricular Hypertrophy:
- High-voltage QRS complexes, especially in the precordial leads (V1-V6).
- ST-segment elevation in the anterior leads (V1-V3), often with T-wave inversions.
Strain pattern with ST-depression and T-wave inversions in the lateral leads14.
Clinical Clues:
- History of hypertension or aortic valve disease.
- Echocardiographic evidence of hypertrophy.
Why LVH Mimics STEMI
The elevated voltage in the anterior leads and associated strain pattern can mimic an anteroseptal infarction. LVH-induced repolarization abnormalities can lead to confusion, especially in the absence of a clear clinical picture of acute coronary syndrome15.
Early Repolarization
Early repolarization is a benign ECG variant most commonly seen in young, healthy individuals, particularly athletes. It represents a variation in the electrical activity of the heart’s repolarization phase16.
ECG Features of Early Repolarization:
- ST-segment elevation, typically concave, in the precordial and inferior leads.
- Notching or slurring of the J-point, especially in the lateral leads.
- No reciprocal ST-segment depression or evolving ECG changes17.
Clinical Clues:
- Asymptomatic or discovered incidentally.
- No associated chest pain or cardiac risk factors16,18.
Why Early Repolarization Mimics STEMI
Early repolarization can closely mimic the ST-elevations seen in anterior or inferior STEMI, especially when J-point notching or slurring is present. Differentiation relies on the absence of clinical symptoms, reciprocal changes, and the stability of the ECG over time16.
Previously Diagnosed Left Bundle Branch Block (LBBB)
LBBB is a conduction abnormality that affects the left ventricle, causing delayed depolarization and abnormal repolarization patterns. While an old, previously diagnosed LBBB is generally not concerning and often reflects underlying structural heart disease or chronic conditions, a new or presumed new LBBB may raise suspicion for an acute myocardial infarction (OMI), especially in the context of other clinical signs of ischemia19,20.
This can be particularly challenging when interpreting the ECG, as LBBB alters the ST-segment, potentially masking or mimicking ischemic changes. In patients with suspected acute coronary syndrome, the presence of new or presumed new LBBB may raise concern for an underlying ischemic event20.
ECG Features of Previously Diagnosed LBBB:
- Wide QRS complexes (>120ms).
- Discordant ST-segments (ST-segment elevation in leads with a predominantly negative QRS and depression in leads with positive QRS complexes).
- Absence of normal septal Q-waves in leads I, aVL, V5, and V621.
Clinical Clues:
- Often seen in patients with underlying cardiomyopathy or ischemic heart disease.
- Symptomatology may range from asymptomatic to severe heart failure19.
How It Mimics STEMI
LBBB creates significant abnormalities in both the depolarization and repolarization of the ventricles, making it difficult to interpret ST-segments. This necessitates the use of additional diagnostic tools, such as coronary angiography, or more sophisticated AI-powered ECG interpretation models, like PMcardio, which can accurately interpret complex conduction abnormalities in LBBB and paced rhythms22.
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Brugada Syndrome
Brugada syndrome is a genetic condition affecting the sodium channels of the cardiomyocytes, specifically through mutations in the SCN5A gene, predisposing individuals to ventricular arrhythmias and sudden cardiac death23,24.
ECG Features of Brugada Syndrome
- ST-segment elevation in the right precordial leads (V1-V3) with a coved or saddleback pattern25.
- T-wave inversion in the right precordial leads.
- Right bundle branch block (RBBB) pattern may also be present26.
Clinical Clues:
- Typically presents in young men with a history of syncope, palpitations, or sudden cardiac arrest23.
- Family history of sudden cardiac death or arrhythmias24.
- Typically presents without chest pain and can be exacerbated by fever, which increases the risk of arrhythmias due to the temperature sensitivity of sodium channels27.
How Brugada Syndrome Mimics STEMI
Brugada syndrome can present with ST-segment elevation in the anterior leads, mimicking a STEMI involving the LAD territory. The absence of reciprocal changes and the coved morphology of the ST-elevation are key distinguishing features25.
Hyperkalemia
Hyperkalemia alters cardiac depolarization and repolarization due to elevated extracellular potassium levels, affecting the resting membrane potential of cardiac myocytes28.
ECG Features of Hyperkalemia:
- Peaked T-waves, particularly in the precordial leads.
- Flattening or absence of P-waves.
- Wide QRS complexes that can merge with ST-segments, creating a sine-wave appearance in severe cases29.
Clinical Clues:
- History of renal failure, potassium-sparing diuretic use, or other causes of hyperkalemia.
- Symptoms of muscle weakness, fatigue, or arrhythmias28,30.
How Hyperkalemia Mimics STEMI
Severe hyperkalemia can cause broad ST-elevation and wide QRS complexes that may resemble ischemic changes on the ECG. The absence of reciprocal changes, the clinical context, and rapid normalization of the ECG after correcting potassium levels are important clues31.
The Role of Advanced Diagnostics in Identifying STEMI Mimics
In the high-pressure environment of emergency care, where minutes matter, distinguishing between true STEMI and STEMI mimics can be a daunting task. While clinical context, patient history, and laboratory findings (such as troponin levels) are essential, the ECG remains the cornerstone of diagnosis. However, traditional ECG interpretation can be challenging in the presence of conduction abnormalities, hypertrophic changes, or benign variants.
This is where PMcardio offers a distinct advantage. By utilizing advanced deep learning algorithms trained on extensive datasets of ECGs, our AI is capable of distinguishing true myocardial infarction from common STEMI mimics with high precision22. The tool analyzes patterns that may be difficult to detect with the naked eye, reducing unnecessary cath lab activations and invasive procedures.
Conclusion
STEMI mimics pose a significant challenge to emergency care providers, with the potential for both over- and under-treatment of patients presenting with chest pain and ST-segment elevation. Careful ECG interpretation, clinical context, and advanced diagnostic tools are essential in differentiating these conditions from true STEMI. PMcardio, the AI-powered ECG platform offers clinicians an invaluable tool in making these critical decisions, ensuring that patients receive the right diagnosis and treatment32,33.
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