Why is ACS a working term?
The term "acute coronary syndrome" is used at the initial stage of care before a definitive diagnosis can be made.
This is due to the challenges of early diagnosis:
- Symptoms of unstable angina and early myocardial infarction are identical.
- The pain episode can last for more than 30 minutes in both cases.
- Specific electrocardiographic changes (ST-segment elevation, Q-wave appearance) and elevated blood levels of cardiospecific enzymes do not appear immediately.
Pathogenesis and classification
The development of ACS is based on atherosclerotic plaque disruption (rupture or erosion). A thrombus forms at the site of injury, partially or completely occluding the lumen of the coronary artery. This causes a severe oxygen deficit in the myocardium.
Depending on the duration and severity of the vascular occlusion, the following develop:
- Reversible ischemia: unstable angina.
- Irreversible injury (necrosis): myocardial infarction.
To determine emergency management tactics, patients are categorized based on the initial ECG results into:
- STEMI (STEMI).
- NSTEMI (NSTEMI).
Diagnostics and differential diagnosis
Initial assessment is based on pain analysis (pressure-like, retrosternal), medical history (previous myocardial infarctions, coronary artery disease), and risk factors (diabetes, hypertension).
An ECG must be recorded within 10 minutes of the first medical contact. If the diagnosis is doubtful, telemedicine is used. If symptoms change, a repeat ECG is performed.
The definitive diagnosis is established within a few hours or days by evaluating ECG dynamics and the levels of cardiac markers (troponins, CK-MB, myoglobin):
- Transmural infarction: Q-wave appears, ST segment shifts upward.
- Non-Q-wave infarction: no ST and Q changes on the ECG, but cardiac enzymes exceed the upper limit of normal by more than 2-fold.
- Unstable angina: ECG remains unchanged, enzymes stay within normal limits.
Important to remember: chest pain may be non-coronagenic (e.g., neuromuscular), and prior ECG abnormalities can complicate diagnosis.
Class and exam questions
What is the difference between ACS and myocardial infarction?
ACS is a provisional diagnosis prior to receiving laboratory results and serial ECGs. Myocardial infarction is a confirmed definitive diagnosis with proven myocardial necrosis.
Why divide ACS into ST-elevation and non-ST-elevation types?
This is essential for rapid decision-making regarding emergency management. ST-elevation indicates total occlusion of a major artery and requires immediate restoration of blood flow.
What to do if the initial ECG shows no changes, but the pain is typical?
Keep the diagnosis of ACS, as electrocardiographic changes may be delayed. It is necessary to monitor the patient, repeat the ECG, and test blood for cardiospecific enzymes.
What else to study on this topic
- Mechanisms of ECG pattern formation in ACS
- Drugs for antiplatelet and anticoagulant therapy
- Dynamics of cardiospecific biomarker levels
- Clinical criteria for unstable angina
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