From the Guidelines
Occlusive myocardial infarction (MI) is characterized by specific ECG patterns, including ST-segment elevation of at least 1 mm in two or more contiguous leads, with the specific leads affected indicating the location of the infarct, as recommended by the 2018 European Society of Cardiology guidelines 1. The ECG patterns of an occlusive MI can be broken down into several key findings:
- ST-segment elevation: This is the hallmark finding of an occlusive MI, with the specific leads affected indicating the location of the infarct. For example, anterior MI shows elevation in V1-V4, inferior MI in leads II, III, and aVF, and lateral MI in leads I, aVL, V5, and V6.
- Pathological Q waves: These develop within hours to days and represent myocardial necrosis. They are defined as Q waves that are ≥0.04 seconds wide and ≥25% of the R wave amplitude.
- Reciprocal ST depression: This often accompanies ST elevation and is seen in leads opposite to the infarct area.
- T wave inversions: These typically follow ST elevation as the infarct evolves. Other findings may include:
- Hyperacute T waves: These are tall, peaked T waves that are seen in early MI.
- Loss of R wave progression: This is seen in precordial leads and can indicate an occlusive MI.
- Bundle branch blocks: These can mask typical ST changes and make diagnosis more challenging. It's worth noting that the ECG criteria for diagnosing an occlusive MI are based on changes of electrical currents of the heart, measured in millivolts, with standard calibration of the ECG being 10mm/mV, as stated in the 2018 European Society of Cardiology guidelines 1. In the proper clinical context, ST-segment elevation is considered suggestive of ongoing coronary artery acute occlusion, with specific criteria for the degree of elevation required in different leads, as outlined in the 2018 European Society of Cardiology guidelines 1. The 2000 joint European Society of Cardiology/American College of Cardiology committee for the redefinition of myocardial infarction also provides guidance on ECG changes indicative of myocardial ischemia that may progress to MI, including ST segment elevation, ST segment depression, and T wave abnormalities 1. However, the most recent and highest quality study, the 2018 European Society of Cardiology guidelines, should be prioritized when making a definitive recommendation 1.
From the Research
ECG Patterns of Occlusive Myocardial Infarction (MI)
The ECG patterns of an occlusive myocardial infarction (MI) can be identified through various studies, including:
- ST-segment elevation myocardial infarction (STEMI) is caused by complete coronary artery occlusion and is characterized by ST-segment elevation on electrocardiography 2
- Non-ST-segment elevation ACS (NSTE-ACS) is caused by partial or intermittent occlusion of the artery and is associated with ST-segment depressions, T-wave inversions, or neither 2
- Occlusion MI (OMI) is based on the presence or absence of acute coronary occlusion (ACO) in the patient, rather than STE on ECG, and can be identified through advanced ECG interpretation aided by artificial intelligence, complementary bedside echocardiography, and advanced imaging 3
Characteristics of Occlusive MI
The characteristics of occlusive MI include:
- Higher mortality rates compared to non-occlusive MI 4
- Fewer comorbidities, but no difference in cerebrovascular disease 4
- Delays to treatment, such as immediate reperfusion therapy 4
- Similar features to STEMI, but no reliable characteristics to identify OMI versus non-OMI 4
Diagnosis and Treatment
The diagnosis and treatment of occlusive MI involve:
- Immediate electrocardiography to distinguish between STEMI and non-ST-segment elevation ACS (NSTE-ACS) 2
- Rapid reperfusion with primary percutaneous coronary intervention (PCI) within 120 minutes for STEMI 2
- Fibrinolytic therapy for patients without access to immediate PCI 2
- High-sensitivity troponin measurements to evaluate for NSTEMI 2
- Prompt invasive coronary angiography and percutaneous or surgical revascularization within 24 to 48 hours for high-risk patients with NSTE-ACS 2