INITIAL THERAPY

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Initial goals are to (1) quickly identify if pt is candidate for reperfusion therapy, (2) relieve pain, and (3) prevent/treat arrhythmias and mechanical complications.

• Aspirin should be administered immediately (162-325 mg chewed at presentation, then 75-162 mg PO qd), unless pt is aspirin-intolerant.
• Perform targeted history, examination, and ECG to identify STEMI (>1 mm ST elevation in two contiguous limb leads, ≥2 mm ST elevation in two contiguous precordial leads, or new LBBB) and appropriateness of reperfusion therapy (percutaneous coronary intervention [PCI] or IV fibrinolytic agent), which reduces infarct size, LV dysfunction, and mortality.
• Primary PCI is more effective than fibrinolysis and is preferred at experienced centers capable of performing the procedure rapidly (Fig. 121-1. Reperfusion Strategies in STEMI), especially when diagnosis is in doubt, cardiogenic shock is present, bleeding risk is increased, or symptoms have been present for >3 h.
• Proceed with IV fibrinolysis if PCI is not available, or if logistics would delay the time between first medical contact and PCI >120 min (Fig. 121-1. Reperfusion Strategies in STEMI). Door-to-needle time for fibrinolysis should be <30 min for maximum benefit. Ensure absence of contraindications (Fig. 121-2. Algorithm for Fibrinolytic Therapy of Acute STEMI) before administering fibrinolytic agent. Those treated within 1-3 h benefit most; can still be useful up to 12 h if chest pain is persistent or ST remains elevated in leads that have not developed new Q waves. Complications include bleeding, reperfusion arrhythmias, and, in case of streptokinase (SK), allergic reactions. Enoxaparin or heparin (60 U/kg [maximum 4000 U], then 12 [U/kg]/h [maximum 1000 U/h]) should be initiated with fibrinolytic agents (Fig. 121-2. Algorithm for Fibrinolytic Therapy of Acute STEMI); maintain activated partial thromboplastin time (aPTT) at 1.5-2.0 × control (∼50-70 s).
• If chest pain or ST elevation persists >90 min after fibrinolysis, consider referral for rescue PCI. Coronary angiography after fibrinolysis should also be considered for pts with recurrent angina or high-risk features (Fig. 121-2. Algorithm for Fibrinolytic Therapy of Acute STEMI) including extensive ST elevation, signs of heart failure (rales, S₃, jugular venous distension, left ventricular ejection fraction [LVEF] ≤35%), or systolic bp <100 mmHg.

The initial management of NSTEMI (non-Q MI) is different (Chap. 122 Unstable Angina and Non-ST-Elevation Myocardial Infarction). In particular, fibrinolytic therapy should not be administered.

ADDITIONAL STANDARD TREATMENT

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(Whether or not reperfusion therapy is undertaken):

• Hospitalize in CCU, or for lower risk pts, in an intermediate care unit with continuous ECG monitoring.
• IV line for emergency arrhythmia treatment.
• Pain control: (1) Morphine sulfate 2-4 mg IV q5-10 min until pain is relieved or side effects develop (nausea, vomiting, respiratory depression [treat with naloxone 0.4-1.2 mg IV], hypotension [if bradycardic, treat with atropine 0.5 mg IV; otherwise use careful volume infusion]); (2) nitroglycerin 0.3 mg SL if systolic bp >100 mmHg; for refractory pain: IV nitroglycerin (begin at 10 µg/min, titrate upward to maximum of 200 µg/min, monitoring bp closely); do not administer nitrates within 24 h of sildenafil or vardenafil, or within 48 h of tadalafil (phosphodiesterase type 5 inhibitors used for erectile dysfunction); (3) β-adrenergic antagonists (see below).
• Oxygen: 2-4 L/min by nasal cannula (if needed, to maintain O₂ saturation >90%).
• Mild sedation (e.g., diazepam 5 mg, oxazepam 15-30 mg, or lorazepam 0.5-2 mg PO three to four times daily).
• Soft diet and stool softeners (e.g., docusate sodium 100-200 mg/d).
• β-Adrenergic blockers (Chap. 119 Hypertension) reduce myocardial O₂ consumption, limit infarct size, and reduce mortality. Especially useful in pts with hypertension, tachycardia, or persistent ischemic pain; contraindications include active CHF, systolic bp <95 mmHg, heart rate <50 beats/min, AV block, or history of bronchospasm. Consider IV (e.g., metoprolol 5 mg q2-5min to total dose of 15 mg) if pt is hypertensive. Otherwise, begin PO regimen (e.g., metoprolol tartrate 25-50 mg four times daily).
• Anticoagulants: Most pts with STEMI should receive an anticoagulant (typically unfractionated heparin [UFH] or bivalirudin for those undergoing PCI [discontinued at end of procedure or shortly thereafter]; enoxaparin [for up to 8 days, or until discharge, whichever is earlier] or UFH [for ≥2 days] for those receiving fibrinolysis or no reperfusion therapy). Continued full-dose IV heparin (PTT 1.5-2 × control) or LMWH (e.g., enoxaparin 1 mg/kg SC q12h) followed by warfarin is recommended for pts with high risk of thromboembolism (severe LV dysfunction, presence of ventricular thrombus, large dyskinetic region in acute anterior MI, or pulmonary embolism). If used, warfarin is continued for 3-6 months.
• Antiplatelet agents: Continue aspirin 162-325 mg daily and an oral P2Y₁₂ platelet receptor antagonist after STEMI (e.g., ticagrelor, clopidogrel, or prasugrel [the latter only if PCI is undertaken]).
• ACE inhibitors reduce mortality in pts following acute MI and should be prescribed within 24 h of hospitalization for pts with STEMI-e.g., captopril (6.25 mg PO test dose advanced to 50 mg PO tid). ACE inhibitors should be continued indefinitely after discharge in pts with heart failure or those with asymptomatic LV dysfunction (ejection fraction ≤40%); if pt is ACE inhibitor intolerant, use ARB (e.g., valsartan or candesartan).
• Aldosterone antagonists (spironolactone or eplerenone 25-50 mg daily) further reduce mortality in pts with LVEF ≤40% and either symptomatic heart failure or diabetes; do not use in pts with advanced renal insufficiency (e.g., creatinine ≥2.5 mg/dL) or hyperkalemia.
• Serum magnesium level should be measured and repleted if necessary to reduce risk of arrhythmias.