Myocardial infarction is death of cardiac myocytes (necrosis) caused by prolonged ischemia. The term acute "usually" refers to the time 6 hours to 7 days following pathologic appearance of the infarct.
The patient may experience ischemic-type chest discomfort with accompanying symptoms of nausea, vomiting, dyspnea, diaphoresis, lightheadedness, dizziness, syncope, fatigue and weakness.
Rapid diagnosis and risk stratification of chest pain patients is important to identify acute myocardial infarction patients who will benefit from reperfusion therapy.
Ideally, patient diagnosed with myocardial infarction should begin treatment within 30 minutes of arrival to hospital.


Rapid diagnosis and risk stratification of chest pain patients are important to identify acute myocardial infarction patients who will benefit from reperfusion therapy

  • Ideally, patient diagnosed with ST-segment elevation myocardial infarction (STEMI) should begin treatment within:
    • 10 minutes if for fibrinolytic therapy in patients not able to meet target time for primary PCI
    • 120 minutes if to undergo primary PCI

Initial Diagnosis of STEMI

  • Patient should present with history of chest pain/discomfort
  • Electrocardiogram (ECG) revealing persistent ST-segment elevations or (presumed) new left bundle-branch block (LBBB)
  • Elevated markers of myocardial necrosis
    • These can confirm diagnosis in the absence of ECG changes
  • 2D echocardiography and perfusion scintigraphy, if available, can be used to look for (presumed) new regional wall motion abnormalities


Patient History

  • Ischemic-type chest discomfort as previously described

Laboratory Tests

Electrocardiogram (ECG)

  • Obtain as soon as possible, preferably within 10 minutes of emergency department (ED) arrival, since even at the early stage, ECG is rarely normal
  • If ECG shows ST-segment elevations or new or presumed new LBBB, then patient should be immediately evaluated for and if no contraindications, given reperfusion therapy
  • ECG changes of AMI are evolutionary
    • Hyperacute changes of a tall peaked T wave
    • ST-segment elevation followed by development of Q wave
    • Then return of ST-segment to isoelectric and T-wave inversion
  • ST-segment elevation
    • New or presumed new ST-segment elevation at the J point in 2 or more contiguous leads should be considered at ≥0.2 mV for men or ≥0.15 mV for women in leads V2-V3 and/or ≥0.1 mV in other leads
  • ST-segment depression and T-wave changes
    • New horizontal or down-sloping ST-segment depression ≥0.05 mV in 2 contiguous leads
    • T-wave inversion ≥0.1 mV in 2 contiguous leads with prominent R wave or R/S ratio >1
  • ECG may be vague in the early hours and may not show ST-segment elevation or new Q waves
    • Repeat or serial ECG should be taken to compare with previous records and detect evolving infarction
    • In posterior infarction, additional recordings (eg V7 and V8) may be helpful

Biochemical Indicators for Detecting Myocardial Necrosis

  • Blood samples should be taken on 1st assessment and 3-6 hours later
  • Preferred biomarker for myocardial damage is cardiac troponin (I or T)
    • An elevated value or maximal concentration of troponin T or I exceeding the decision limit at least once within the 1st 24 hours after the index clinical event
  • If cardiac troponin assays are not available, CK-MB assay is the preferred alternative
    • Maximal CK-MB exceeding the 99th percentile of the values for a reference control group on 2 consecutive samples or
    • Maximal value over 2x the upper limit of normal for the specific institution at least once during the 1st hour following the index clinical event
    • Values for CK-MB should rise and fall; if the values remain elevated without change this is typically not due to myocardial infarction (MI)


  • Helpful in detecting wall motion abnormalities or loss of viable myocardium in the presence of elevated biomarker values
  • Without any delay to therapy, obtain chest x-ray
  • Perform chest x-ray, transthoracic and/or transesophageal echocardiography, contrast chest computed tomographic (CT) scan or magnetic resonance imaging (MRI) scan, to differentiate ST-segment elevation myocardial infarction (STEMI) from aortic dissection in a doubtful presentation
  • Perform echocardiography to ensure STEMI diagnosis and allow risk stratification of patients with chest pain upon ED arrival especially with presence of LBBB or pacing and suspicion of posterior STEMI with anterior ST-segment depressions
  • Transthoracic echocardiography may provide evidence of focal wall motion abnormalities and facilitate triage in patients with ECG findings that are difficult to interpret


  • Patients who present with persistent ST-segment myocardial infarction or new or presumed new LBBB should undergo early mechanical (percutaneous coronary intervention or PCI) or pharmacological (fibrinolytic) reperfusion unless they have contraindications

In institutions that are experienced in percutaneous coronary intervention (angioplasty and/or stenting)

  • If PCI can be performed within 90 minutes after the 1st medical contact, this is the preferred therapeutic option

In institutions that are not experienced in percutaneous coronary intervention

  • If there are no contraindications, fibrinolytic therapy should be started within 30 minutes in STEMI patients presenting to a hospital without PCI capability and who cannot be transferred to a PCI center and undergo PCI within 90 minutes
  • Careful individual assessment needs to be made of the potential benefits of mechanical reperfusion vs risks of treatment delay and transportation to the nearest interventional catheterization lab

Mechanical reperfusion should be considered in:

  • Patients with contraindications to intravenous fibrinolytic therapy
  • Patients presenting with cardiogenic shock

Goal is to administer reperfusion treatment within 30 minutes of patient arriving at hospital for fibrinolytic therapy and within 90 minutes of patient arriving at hospital for percutaneous coronary intervention

Inclusion Criteria for Intravenous (IV) Fibrinolytic Therapy

  • Symptoms consistent with AMI
  • ST-segment elevation on ECG 
  • New or presumably new bundle-branch block (that is obscuring ST-segment analysis) and history of MI symptoms
  • Time to therapy from onset of angina: <12 hours; most beneficial if <6 hours
    • No significant benefit if >12 hours, except in patients with ongoing ischemia and ST-segment elevation on ECG 

Absolute Contraindications

  • Previous hemorrhagic stroke or stroke of unknown origin at any time
  • Ischemic stroke within 3 months except acute ischemic stroke within 4.5 hours
  • Known intracranial neoplasm or central nervous system damage
  • Significant closed-head or facial trauma within 3 months
  • Known structural cerebral vascular lesion (eg arteriovenous malformation)
  • Aortic dissection (confirmed or suspected)
  • GI bleeding within the last month
  • Active bleeding or bleeding diathesis (does not include menses)
  • Surgery within 2 months intracranially or intraspinally
  • Severe uncontrolled hypertension that is unresponsive to emergency therapy
  • For Streptokinase: Prior treatment within the previous 6 months

Relative Contraindications

Risks versus benefits must be considered

  • Uncontrolled or refractory hypertension on presentation (SBP >180 mmHg and/or DBP >110 mmHg); history of severe uncontrolled hypertension
  • Transient ischemic attack within >3 months
  • Taking oral anticoagulants
  • Traumatic or refractory resuscitation
  • For Streptokinase/Anistreplase: Prior exposure (especially within 5 days–12 months) or prior allergic reaction
    • Antibodies may be present and can impair the action of the agent
  • Pregnancy
  • Active peptic ulcer disease
  • Advanced liver disease
  • Infective endocarditis
  • Dementia
  • Major surgery within <3 weeks
  • Internal bleeding within 2-4 weeks
  • Non-compressible vascular punctures
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