EKG
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The classic STEMI presentation is now understood to be just one manifestation of a broader spectrum of acute coronary occlusion. While the "tombstone" ST elevation is the most widely recognized ECG finding, it is far from the only one. The 2025 Australian Clinical Guideline for Diagnosing and Managing Acute Coronary Syndromes has formally introduced the terminology of Acute Coronary Occlusion Myocardial Infarction (ACOMI), recommending broader recognition of ECG patterns beyond ST-segment elevation alone.

Understanding which leads show ST elevation also tells you which coronary artery is likely blocked. Inferior STEMI (leads II, III, aVF) typically involves the right coronary artery or left circumflex. Anterior STEMI (leads V1–V4) usually indicates left anterior descending artery occlusion—the so-called "widowmaker." Lateral STEMI (leads I, aVL, V5, V6) often involves the left circumflex artery. Recognizing these patterns helps anticipate complications and guides emergent management decisions. But as the next chapter explains, not every dangerous occlusion announces itself with ST elevation.

The traditional approach to heart attacks has long been to classify them as either STEMI (with clear ST elevation on an ECG, presumed to be a complete blockage) or NSTEMI (without such elevation, often considered a partial blockage). However, cardiology is now undergoing a major shift because many patients with a completely occluded coronary artery—and ongoing, extensive heart muscle death—never show classic ST elevation on their ECG. Research has shown that more than half of patients with an occluded artery will not show ST-segment elevation, and this can lead to delays in care and worse outcomes.

This realization has given rise to the concept of Occlusion MI (OMI), which asks not "Does the ECG have ST elevation?" but rather "Is there an acutely occluded artery?" The OMI paradigm shifts the focus from rigid ECG thresholds to a pathophysiology-based strategy that integrates clinical assessment, ECG interpretation, and adjunct diagnostic modalities to actively seek evidence of acute coronary occlusion. As Stephen Smith, MD, a leading proponent of this paradigm, has stated: "We think we should get rid of the term ST-elevation MI, because it focuses on ST-elevation and makes you think that ST-elevation is all that matters—when what matters is acute coronary occlusion without collateral circulation leading to imminent myocardial necrosis or death."

Several so-called STEMI equivalents can indicate a dangerous occlusion even when the ST segment is not elevated. These patterns require the same urgency as classic STEMI because they signify the same underlying pathology: an acutely occluded coronary artery causing ongoing myocardial necrosis. Missing these patterns leads to delays in reopening the artery, which directly costs heart muscle. Studies confirm that STEMI criteria are a poor surrogate marker for acute coronary occlusion, and that OMI signs have approximately double the sensitivity with preserved high specificity. The key STEMI equivalents include:

Posterior MI. When the back wall of the heart is infarcted, the standard 12-lead ECG may show only ST depression in leads V1–V3 rather than elevation anywhere. Deep, horizontal ST depression in V1–V3, often accompanied by tall R waves and upright T waves, should raise immediate suspicion. Posterior leads (V7–V9) can confirm the diagnosis by revealing ST elevation ≥0.5 mm, but treatment should not be delayed.

De Winter Pattern. First described in 2008 in the New England Journal of Medicine, this pattern is associated with proximal LAD occlusion. It is characterized by 1–3 mm of upsloping ST depression at the J-point in precordial leads (typically V1–V4), which continues into tall, symmetric T waves. There is often 1–2 mm of ST elevation in lead aVR. This is considered a STEMI equivalent requiring emergent catheterization.

Wellens Syndrome. This pattern is associated with critical stenosis of the proximal LAD, characterized by deeply inverted or biphasic T waves in V2–V3, which may extend to V1–V6. Critically, these changes typically appear when the patient is pain-free. Wellens syndrome carries up to 99% specificity for significant LAD stenosis.

Sgarbossa Criteria for Left Bundle Branch Block. Diagnosing acute MI in the presence of LBBB is notoriously difficult. The Sgarbossa criteria and the Smith-modified Sgarbossa criteria (using the ST/S ratio) provide validated methods for detecting acute occlusion in patients with LBBB or ventricular paced rhythms.

To help address the challenge of detecting these subtle patterns, artificial intelligence tools such as PMcardio are being developed. The PMcardio AI-ECG model (also known as the "Queen of Hearts") has been trained on millions of ECGs to detect occlusive myocardial infarction patterns that may be missed by conventional STEMI criteria. In one study, the AI model outperformed STEMI criteria in terms of accuracy (90.9% vs 83.6%) and sensitivity (80.6% vs 32.5%), with similar specificity (93.7% vs 97.7%).

Some experts express concern about false positives and unnecessary cath lab activations, but the goal is to augment clinical judgment, not replace it. As Smith notes, "It can see these waveform differences, just like it can recognize a face. It can recognize OMI on an EKG."

Practical Takeaway: A normal-looking ST segment does not rule out a major heart attack. If a patient has concerning symptoms and the ECG shows any of these higher-risk patterns, do not wait for textbook ST elevation. Emergently consult cardiology, consider activating the cath lab, and treat the patient as having a possible occlusion MI.

The ECG patterns covered in this preview represent a foundation. Continued education and exposure to tracings are essential for developing the pattern-recognition skills that distinguish expert interpreters. The following resources offer case-based learning, detailed explanations, and additional practice with both classic STEMI presentations and the more subtle STEMI equivalents.

Recommended External Resources

The complete book provides dozens more resources, video tutorials, and interactive ECG quizzes.