Reperfusion therapy (mechanical or pharmacologic) is indicated for patients with chest pain consistent with a myocardial infarction with a duration of 12 hours or less in association with ST-segment elevation greater than 0.1 mV in two or more contiguous electrocardiographic leads or a new (or presumed new) left bundle-branch block. Candidates for reperfusion therapy should be identified by an emergency department physician; the process can be initiated by emergency-medical-services personnel to minimize delay.
Primary PCI is preferred if a skilled interventional cardiologist and catheterization laboratory with surgical backup are available and if the procedure can be performed within 90 minutes after initial medical contact with the patient. For patients initially presenting to a hospital that does not have interventional capabilities, rapid transfer to such a facility is recommended.
Primary PCI is preferable for certain patients even if the interval between the first medical contact and the procedure (the “door-to-balloon” interval) exceeds 90 minutes. Such patients include those with a contraindication to fibrinolytic therapy20; those with a high risk of bleeding with fibrinolytic therapy, including patients 75 years of age or older (for whom the risk of intracranial hemorrhage with fibrinolytic therapy is increased); those with clinical findings (i.e., tachycardia, hypotension, or pulmonary congestion) suggesting a high risk of an infarct-related complicated medical course or death22; and those with cardiogenic shock.
Fibrinolytic therapy is preferred for patients whose first medical contact occurs less than 3 hours after the onset of symptoms but for whom PCI is not immediately available, those who seek medical attention less than 1 hour after the onset of symptoms (in whom the therapy may abort the infarction), and those with a history of anaphylaxis due to radiographic contrast material.
As compared with patients who undergo balloon angioplasty, among those who undergo bare-metal stenting of the infarct-related artery, the rates of restenosis and the frequencies of recurrent angina and repeated revascularization procedures are lower. As a result, stenting of the infarct-related artery is usually preferred. However, balloon angioplasty is preferred for patients in whom clopidogrel (Plavix, Bristol-Myers Squibb) is contraindicated (because of thrombocytopenia or the presence of left main or extensive multivessel coronary artery disease, who may require bypass surgery within days after successful primary PCI). Balloon angioplasty is also preferred when the size of the infarct-related artery is insufficient for the placement of a stent.
As compared with bare-metal stents, drug-eluting stents appear to reduce further the rates of restenosis within 12 months after primary PCI. If drug-eluting stents are used in this setting, it is imperative that dual antiplatelet therapy (aspirin and clopidogrel) be given for at least 12 months; otherwise, subacute thrombosis may occur. There are no good data on longer-term outcomes.
In addition to oral aspirin and intravenous unfractionated heparin, patients with a myocardial infarction with ST-segment elevation should receive oral clopidogrel after it has been determined that emergency bypass surgery is not required. Beta-adrenergic blockers and angiotensin-converting–enzyme inhibitors should be initiated, provided that the patient has no contraindications and is stable hemodynamically. Platelet glycoprotein IIb/IIIa inhibitors or antibodies often are given to patients undergoing primary PCI. Treatment with a high dose of a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor (statin) is recommended for all patients with acute myocardial infarction.
The monetary costs of fibrinolytic therapy and primary PCI are similar. Primary PCI is an expensive procedure, with professional fees ranging from approximately $4,000 to $5,000 and hospital charges ranging from approximately $20,000 to $25,000 in the United States. However, patients receiving fibrinolytic therapy have higher subsequent costs, because of higher rates of in-hospital morbidity and mortality and longer hospital stays.
In a report on 4366 primary PCIs performed at 40 sites in the United States between 1990 and 1994, the success rate (the proportion of patients with a patent infarct-related artery at the end of the procedure) was 91.5%. However, although antegrade flow in the epicardial coronary artery may appear normal after most of these procedures, perfusion of the tissue at the microvascular level is restored to normal in only a minority of patients. In some patients, embolization of microscopic debris with balloon inflation or stent deployment compromises tissue perfusion. In such patients, the magnitude of the ST-segment elevation does not diminish, even though antegrade flow in the epicardial artery is restored. Among these patients, survival is correspondingly reduced.
In about 15% of patients undergoing primary PCI, initial angiography shows a patent infarct-related artery. In these patients, it is presumed that spontaneous fibrinolysis occurred before angiography. In comparison with patients who have diminished or no antegrade flow, these patients are less likely to have hemodynamic instability or left ventricular systolic dysfunction with congestive heart failure or to die as a result of myocardial infarction.