CARDIOVASCULAR NEWS

                            1999 ACC/AHA Acute Myocardial Infarction Guidelines
 

     
         
    The American College of Cardiology (ACC) and the American Heart Association (AHA) have updated their recommendations for the management of patients with acute myocardial infarction, which was previously published in November 1996. The updated version is posted on their websites prior to its publication in the Journal of the American College of Cardiology.


     The updated guidelines highlight the following recommendations:

• Glycoprotein (GP) IIb/IIIa Inhibitors are recommended in patients having a myocardial infarction (MI) without ST-segment elevation

     who have some high risk features and/or refractory ischemia provided they don’t have a major contraindication due to a bleeding risk.

    Three agents are available for clinical practice: (1) Abciximab is a chimeric Fab fragment of a monoclonal antibody to the GP IIb/IIIa receptor. (2) Eptifibatide is a cyclical heptapeptide, which binds to the receptor with a short half-life. (3) Tirofiban is a small nonpeptide compound that also has a short half-life. Direct comparisons of the agents are not available, so the specific choice of which agent to use is speculative.

• Low molecular weight heparin (LMWH) for non – ST elevation acute coronary syndromes (ACS)

    Four trials have compared the use of LMWH and unfractionated heaprin (UFH) for non – ST elevation ACS. In 2 trials, a clear benefit of LMWH was observed, whereas in another, LMWH was superior to placebo. The fourth trial did not show a clear difference in outcomes.

Enoxaparin for the acute management of patients with unstable angina/non–Q-wave MI has been shown to be superior to UFH for reducing death and serious cardiac ischemic events.

    In addition to its convenience, LMWH can be administered subcutaneously with high bioavailability. LMWH has a number of theoretical benefits over unfractionated heparin (UFH). These include the potential to prevent thrombin generation as well as inhibit thrombin, the lack of a need to monitor with coagulation testing, and a lower rate of heparin-associated thrombocytopenia.

• Intravenous UFH or LMWH subcutaneously for patients with non-ST elevation MI.

      • Intravenous heparin is recommended in patients undergoing reperfusion therapy with alteplase. The recommended regimen is 60 U/kg as a bolus at initiation of alteplase infusion, then an initial maintenance dose of approximately 12 U/kg per hour (with a maximum of 4000 U bolus and 1000 U/h infusion for patients weighing >70 kg), adjusted to maintain aPTT at 1.5 to 2.0 times control (50 to 70 seconds) for 48 hours. Continuation of heparin infusion beyond 48 hours should be considered in patients at high risk for systemic or venous thromboembolism.

    • Subcutaneous UFH (eg, 7500 U b.i.d.) or LMWH (eg, enoxaparin 1 mg/kg b.i.d.)(7500 U twice daily) is recommended in all patients not treated with thrombolytic therapy who do not have a contraindication to heparin. In patients who are at high risk for systemic emboli (large or anterior MI, AF, previous embolus, or known LV thrombus), intravenous heparin is preferred.

   • Intravenous heparin in patients treated with nonselective thrombolytic agents (streptokinase, anistreplase, urokinase) who are at high risk for systemic emboli (large or anterior MI, AF, previous embolus, or known LV thrombus).

    It is recommended that heparin be withheld for six hours and that aPTT testing begin at that time. Heparin should be started when aPTT returns to less than two times control (about 70 seconds), then infused to keep aPTT 1.5 to 2.0 times control (initial infusion rate about 1000 U/h). After 48 hours, a change to subcutaneous heparin, warfarin, or aspirin alone should be considered.

• Bypass surgery or angioplasty is preferred for the treatment of cardiogenic shock patients under 75 years of age.

• Consideration for emergency CABG should be given for acute MI patients with severe, diffuse, multivessel disease and who are not candidates for or who have undergone unsuccessful thrombolytic therapy and/or PTCA, and who are within 4 to 6 hours of onset of MI. In the case of patients with cardiogenic shock whose coronary anatomy is unsuitable for PTCA, this time window can extend to 18 hours from the onset of shock.

• Emergency surgical repair in All Postinfarction Ventricular Septal Defect
Although emergency surgical repair was formerly thought to be necessary only in patients with pulmonary edema or cardiogenic shock, it is now recognized as equally important in hemodynamically stable patients.

      Because all septal perforations are exposed to sheer forces and necrotic tissue removal processes by macrophages, the rupture site can abruptly expand, resulting in sudden hemodynamic collapse even in patients who appear to be clinically stable with normal left ventricular function. For this reason, prompt insertion of an intra-aortic balloon pump and referral for emergency operation are recommended for every patient with acute VSD as soon as the septal rupture is diagnosed. Simultaneous CABG, if feasible, seems warranted in patients with extensive coronary artery disease.

• Hormone replacement therapy should not be started after MI but can be continued in women who were receiving it prior to MI.©