myocardial%20infarction%20w_%20st-segment%20elevation
MYOCARDIAL INFARCTION W/ ST-SEGMENT ELEVATION
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.

Emergency Department and Acute Care Measures

  • Secure venous access
  • Record pulse and blood pressure (BP)

Do pertinent lab exams promptly

  • Do 12-lead ECG within 10 minutes
  • Draw blood for cardiac markers, glucose, lipid profile

Administer Oxygen

  • Oxygen (O2) at 2-4 L/min should be administered to all patients and especially to patients who have features of heart failure (HF) or shock, have oxygen saturation (SaO2) <90%, or are breathless, preferably within 6 hours
    • Administer via nasal prongs or face mask

Patient and Caregiver Reassurance

  • Patient will probably have anxiety from the thought of a heart attack and from the pain
  • It is helpful to reassure the patient and their caregivers; this may decrease their anxiety

Pharmacotherapy

Emergency Department and Acute Care

Aspirin

  • Should be given promptly and ideally within the 1st 24 hours of suspected MI unless there are contraindications
  • When dose >160 mg is given, Aspirin gives rapid clinical antithrombotic action which is caused by near-total and immediate inhibition of thromboxane A2 production
  • Treatment of evolving AMI with Aspirin with or without thrombolytics has shown to reduce mortality

Relief of Pain

  • Opioid (IV)
    • Should be administered promptly at the time of diagnosis
    • Eg Morphine (analgesic of choice for STEMI-related pain), Diamorphine
    • Pain is associated with sympathetic activation that results in vasoconstriction and an increase in the workload of the heart
    • Avoid MI administration
    • Use with caution in inferior wall or posterior wall MI
    • Anti-emetics may be given concurrently with opioids to minimize nausea
  • Tranquilizer may be helpful in anxious patients
  • NSAIDs (except Aspirin) and COX-2 inhibitors should be discontinued, if regularly used prior to AMI, due to association with increased cardiovascular risk and prothrombotic effects

Reperfusion with Thrombolytic Therapy (IV)

  • IV thrombolytics should be administered to patients with minimum delay in those with confirmed MI and do not have contraindications
    • “Door to needle” time should be within 30 minutes from arrival at the hospital
    • The most benefit is seen when administered <6 hours after onset of symptoms
    • Lesser, but still important benefit is seen when given 6-12 hours after onset of symptoms
    • Should not be given >12 hours after symptom onset except in patients with ongoing ischemia and ST-elevation on ECG 
  • Proven to decrease morbidity and mortality when AMI is treated promptly with Aspirin and thrombolytic regimens
  • Choice of agent will depend on an individualized assessment of risk and benefit, availability and cost
    • For late-treated patients (>6 hours), fibrin-specific agents may be more effective
    • Fibrin non-specific agents (eg Streptokinase and Anistreplase)
    • Fibrin-specific agents [eg Alteplase (t-PA), Reteplase (r-PA), Tenecteplase (TNK-tPA)]
  • Monitor ST-segment elevation, cardiac rhythm, clinical symptoms 1-3 hours after thrombolytic therapy

Fibrinolytic Agents

Streptokinase

  • Not fibrin specific and less efficacious than fibrin selective agents
  • Antigenic and promotes antibodies production

Alteplase

  • Fibrin specific and has better reperfusion at 90 minutes
  • Heparin should be given for 48 hours due to high rate of reocclusion

Tenecteplase

  • 2nd generation fibrin-specific agent that has a slightly lower bleeding risk
  • Given as single or double bolus injections that do not induce production of antibody
  • Heparin should be given for 48 hours

Ancillary Therapy

  • Patients undergoing reperfusion with thrombolytic therapy should be given anticoagulant therapy for ≥48 hours up to 8 days
    • If anticoagulant therapy should be given >48 hours, unfractionated Heparin (UFH) should not be used due to risk of Heparin-induced thrombocytopenia
    • UFH, Enoxaparin and Fondaparinux have established efficacy as ancillary anticoagulant regimens
  • Patients undergoing reperfusion with primary percutaneous coronary intervention (PCI) should be given supportive anticoagulant therapy
    • UFH, Enoxaparin, Bivalirudin are recommended
    • If Fondaparinux is used, anticoagulant with anti-IIa activity (eg UFH, Bivalirudin) should be added

Unfractionated Heparin (UFH)

  • Important adjunctive therapy after t-PA derived agents [(t-PA), (r-PA), (TNK-tPA), Streptokinase or Anistreplase]
    • Intravenous UFH for 48 hours and continue in patients at high risk of thromboembolism
  • If patient is at high risk of venous thromboembolism (VTE), they should receive intravenous UFH for 48 hours then consider converting to subcutaneous Heparin, Warfarin or Aspirin
    • High-risk patients: Anterior myocardial infarction, existing HF, previous embolus, atrial fibrillation (A-fib) or left ventricular (LV) thrombus

Direct Thrombin Inhibitor

Bivalirudin

  • Useful supportive anticoagulant for primary PCI with or without prior treatment with UFH 
  • Can be considered in STEMI patients who will undergo PCI and are at high risk of bleeding
  • Not recommended as an alternative to UFH in patients who received thrombolytic therapy with Streptokinase to avoid excess major bleeding

Low-Molecular-Weight Heparin

Enoxaparin

  • Can also be used to support rescue PCI
  • No additional anticoagulant needed
  • Use is indicated for patients with creatinine <2.5 mg/dL (190.6 µmol/L) in men and <2.0 mg/dL (152.5 µmol/L) in women
  • Preferred over UFH for anticoagulation extending beyond 48 hours

Factor Xa Inhibitor

Fondaparinux

  • When used alone to support PCI, there is increased risk for catheter thrombosis, therefore, use of additional anticoagulant with anti-IIa activity is warranted
  • Use is indicated for patients with creatinine <3.0 mg/dL (228.7 mmol/L)

Further Inpatient Treatment

Dual Antiplatelet Therapy (DAPT)

  • Eg Aspirin + Clopidogrel/Prasugrel/Ticagrelor (P2Y12 inhibitors)
  • After PCI (bare-metal stents or drug-eluting stents), P2Y12 inhibitor therapy is given for at least 12 months; after coronary artery bypass graft (CABG), P2Y12 inhibitor therapy is resumed to complete 12 months of DAPT
  • Continuation of DAPT for >12 months may be reasonable if there is no high risk of bleeding and no significant overt bleeding on DAPT
  • Aspirin
    • Standard 1st-line antiplatelet therapy
    • Should be administered daily and continued indefinitely to all patients without contraindications
    • 75-100 mg of Aspirin is recommended in patients being treated with dual antiplatelet therapy 
  • Clopidogrel
    • May be a useful substitute for Aspirin in patients receiving fibrinolytic therapy who cannot tolerate or have contraindications to Aspirin
      • Clopidogrel should be given for a minimum of 14 days to at least 12 months in patients treated with DAPT in conjunction with fibrinolytics
    • In combination with Aspirin, Clopidogrel is recommended in STEMI patients in whom a medical procedure or PCI is planned
    • Should be given in STEMI patients up to 75 years of age who are receiving fibrinolysis, Aspirin and Heparin
    • If CABG is to be performed, intake of Clopidogrel should be withheld 5 days prior to procedure
  • Prasugrel
    • In combination with Aspirin, Prasugrel is recommended in STEMI patients in whom PCI is planned
    • Not recommended if patient has received fibrinolytic therapy prior to PCI
    • If CABG is to be performed, intake of Prasugrel should be withheld 7 days prior to procedure
  • Ticagrelor
    • In combination with Aspirin, Ticagrelor is recommended in STEMI patients who will undergo PCI, CABG, or medical management
      • Not recommended if patient has received fibrinolytic therapy prior to PCI 
    • Ticagrelor is preferred over Clopidogrel for maintenance P2Y12 inhibitor therapy in patients treated with DAPT following implantation of a coronary stent 
    • Should be withheld 3-5 days prior to CABG
  • Glycoprotein IIb/IIIa Inhibitors
    • Adjunctive use of Abciximab, Eptifibatide or Tirofiban at the time of primary PCI can benefit patients with large thrombus burden or those who have not been given adequate loading of P2Y12 inhibitor (Clopidogrel or Prasugrel or Ticagrelor)
    • Eptifibatide or Tirofiban should be discontinued at least 2-4 hours and Abciximab at least 12 hours before urgent CABG

Anticoagulants

  • Eg UFH, Enoxaparin, Fondaparinux
  • Beneficial in MI with ST elevation
    • May also be given to patients treated with fibrin-selective lytic agents, as routine administration after fibrinolysis, and patients with atrial fibrillation or mural thrombus
  • In patients with STEMI who do not undergo reperfusion therapy, anticoagulants (LMWH or Fondaparinux) may be given using the same dosing regimens for patients who receive fibrinolytic therapy
  • When Fondaparinux is used alone to support PCI, there is increased risk for catheter thrombosis; therefore, use of additional anticoagulant with anti-IIa activity (eg UFH or Bivalirudin) is warranted
  • Use is contraindicated for patients with creatinine <30 mL/minute

Beta-Blocker

  • Oral beta-blockers should be given within 24 hours of onset of infarction in low-risk patients without contraindications (eg hypotension or evidence of low output state, congestive heart failure (CHF), increased risk for cardiogenic shock, PR interval >0.24 seconds, 2nd- or 3rd-degree heart block, active asthma or reactive airway disease)
  • When given during 1st few hours of infarct, beta-blockers may lessen myocardial oxygen (O2) demand by decreasing heart rate, systemic arterial pressure and myocardial contractility

ACE Inhibitor

  • Start in all patients once the blood pressure is stable and systolic blood pressure remains >100 mmHg unless contraindicated (ideally within the 1st 24 hours and after thrombolytic therapy)
    • Greatest benefit has been seen in patients with HF, anterior infarction, LV dysfunction
  • Associated with small but significant decrease in 30-day mortality with most of the benefit seen in the 1st week after infarction

Angiotensin II Antagonist

  • Administer to any patient intolerant of ACE inhibitors and with clinical or radiological signs of HF or LVEF <40%
  • Use with caution in inferior wall or posterior wall MI

Nitrates

  • May be considered in the 1st 24-48 hours if needed in patients with continuing chest pain/ischemia, heart failure, large anterior infarction or hypertension
  • Beyond 48 hours may be used if patient has recurrent angina or continued pulmonary congestion
  • Intravenous route is usually preferred in early management (1st 48 hours) because of more precise control
  • Nitrate-induced relaxation of the vascular smooth muscle in veins, arteries and arterioles which results in vasodilation
    • This reduces right ventricular and left ventricular preload along with afterload reduction which decreases cardiac work and myocardial oxygen demand

Calcium Antagonists

  • Eg Diltiazem or Verapamil
  • Should only be considered if beta-blockers and nitrates are ineffective in controlling ischemia or if beta-blockers are contraindicated
  • May be used to control rapid ventricular response with A-fib after AMI
  • Should not be used in patients with CHF, LV dysfunction or atrioventricular (AV) block
  • Have not been shown to reduce mortality after AMI 

Aldosterone Antagonist (Mineralocorticoid Receptor Antagonist)

  • Eg Eplerenone
  • When added to beta-blocker and ACE inhibitor, aldosterone antagonist has been shown to reduce mortality and hospitalization rates in post-myocardial infarction patients with impaired left ventricular function and mild heart failure

Glucose Control

  • Insulin infusion may be used to achieve and maintain normal blood glucose levels of <180 mg/dL (10 mmol/L) according to recommendations from American College of Cardiology Foundation/American Heart Association (ACCF/AHA) 2013 or <200 mg/dL (<11 mmol/dL) based on European Society of Cardiology (ESC) 2012 recommendations, while avoiding hypoglycemia (90 mg/dL or <5 mmol/dL) in acute myocardial infarction (AMI) patients with complicated or uncomplicated course

Non-Pharmacological Therapy

Routine Measures For Acute Myocardial Infarction (AMI) Patients

Bed Rest

  • 12-24 hours of complete bed rest at which time it will be apparent whether infarction is complicated or not
  • Uncomplicated cases
    • Early ambulation is encouraged
    • Patient may sit out of bed late on the 1st day and be allowed to use commode, perform self-care and self-feeding
    • Ambulation can start the next day (eg walking flat surface up to 200 meters and upstairs within a few days)
  • Complicated cases (eg heart failure, shock or serious arrhythmias)
    • Will need bed rest longer and physical activity should be increased gradually based on extent of myocardial damage and symptoms
    • Consider risk of thrombus formation and appropriate prophylaxis

Monitor Patient

  • Vital signs, pulse oximetry and ECG should be continuously monitored

Oxygen

  • Administer oxygen if patient has hypoxemia [oxygen pressure (pO2) <94%]
  • In uncomplicated cases, oxygen is usually needed only for the 1st day
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