Sunday, May 9, 2010

AMIs and thrombolysis

ECG changes indicating AMI

  • High probability of MI: persistent ST elevation of ≥ 1 mm in two contiguous limb leads or ST-segment elevation of ≥ 2 mm in two contiguous chest leads or the presence of new LBBB.
  • Intermediate probability of MI: are ST depression, T-wave inversion, and other nonspecific ST-T wave abnormalities.
  • Q waves = old MI


Management options

  • Patients with persistent ST elevation should be considered for reperfusion therapy (thrombolysis or primary PCI).
  • Those without ST elevation will be diagnosed with either NSTEMI if cardiac marker levels are elevated or with unstable angina if serum cardiac marker levels provide no evidence of myocardial injury. Patients presenting with no ST-segment elevation are not candidates for immediate thrombolytics but should receive anti-ischemic therapy and may be candidates for PCI urgently or during admission.

Medical Management

  • Aspirin (300 mg) should be given unless already taken or contraindicated (grade A recommendation), and should preferably be given early (eg, by emergency or ambulance personnel).
  • Clopidogrel should be given in addition to aspirin for patients undergoing PCI with a stent (loading-dose of 300600 mg), or for fibrinolytic therapy (300 mg). Clopidogrel 75 mg daily should be continued for at least a month after fibrinolytic therapy, and for up to 12 months after stent implantation, depending on the type of stent.
  • Antithrombin therapy to inhibit the coagulation cascade, and for patients underdoing PCI. For patients getting streptokinase, whether to heparinise depends on the anti-thrombotic agent. Clexane (enoxaparin) bolus should be dosed at 0.75 mg/kg.
  • Administer a platelet glycoprotein (GP) IIb/IIIa-receptor antagonist (eptifibatide, tirofiban, or abciximab) in addition to aspirin and unfractionated heparin, to patients with continuing ischemia or with other high-risk features and to patients in whom PCI is planned.
  • An ACE inhibitor (Captopril) should be given orally within the first 24 hours of STEMI to patients with anterior infarction, pulmonary congestion, or left ventricular ejection fraction (LVEF) less than 40% in the absence of hypotension.
  • An angiotensin receptor blocker (valsartan or candesartan) should be administered to patients with STEMI who are intolerant of ACE inhibitors and who have either clinical or radiological signs of heart failure or LVEF less than 40%.

Contraindications for fibrinolytic use in STEMI

Absolute contraindications:
  • Prior intracranial hemorrhage (ICH)
  • Known structural cerebral vascular lesion
  • Known malignant intracranial neoplasm
  • Ischemic stroke within 3 months
  • Suspected aortic dissection
  • Active bleeding or bleeding diathesis (excluding menses)
  • Significant closed-head trauma or facial trauma within 3 months
Relative contraindications:
  • History of chronic, severe, poorly controlled hypertension
  • Severe uncontrolled hypertension on presentation (SBP >180 mm Hg or DBP >110 mm Hg)
  • Traumatic or prolonged (>10 min) CPR or major surgery less than 3 weeks
  • Recent (within 2-4 wk) internal bleeding
  • Noncompressible vascular punctures
  • For streptokinase/anistreplase - prior exposure or prior allergic reaction to these agents
  • Pregnancy
  • Active peptic ulcer
  • Current use of anticoagulant (eg, warfarin sodium) that has produced an elevated international normalized ratio (INR) >1.7 or prothrombin time (PT) >15 seconds

Follow-up Patient Care

  • Patients should continue to receive beta-blockers, nitrates, and heparin, as indicated.
  • ACE inhibitors have been shown to improve survival rates in patients who have experienced an MI. In the acute setting, afterload reduction from ACE inhibitors may reduce the risk of CHF and sudden death.