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Commentary: Selecting the Best Reperfusion Strategy in ST-Elevation Myocardial Infarction: It's All a Matter of Time

Circulation 2003;108: 2828 - 2830
Authors: R. P. Giugliano, E. Braunwald

Restoration of epicardial flow, regardless of the method used, can abort infarction within the first 30 minutes after coronary occlusion, and the benefit of fibrinolytic therapy compared with placebo is considerably higher in patients treated within 2 hours after symptom onset than in those treated later. Although successful reperfusion between 30 minutes and 2 hours can result in considerable myocardial salvage, only a minority of patients comes into contact with medical personnel within this time interval. Indeed, a large US registry showed that the combination of delays in patient presentation and those inherent in an interventional strategy result in only 8% of patients receiving primary PCI within 2 hours of symptom onset.
With successful reperfusion more than 2 to 3 hours after symptom onset, myocardial salvage is reduced (particularly with fibrinolytic therapy), preservation of the myocardium becomes more dependent on preexisting collateral flow, and recovery of left ventricular function is modest. Primary PCI with adjunctive glycoprotein IIb/IIIa inhibitor may improve myocardial salvage compared with pharmacological reperfusion. There are, however, other potential benefits of an open infarct-related artery: perfusion of hibernating myocardium, improved healing, the prevention of infarct expansion, and of ventricular remodeling. Because PCI is very effective (>90%) at restoring epicardial flow and improving microvascular flow even hours after coronary occlusion, it is especially well suited in patients who present relatively late. Although progressively longer delays in time to presentation are associated with higher rates of complications after fibrinolysis, the same pattern appears less evident for primary PCI.

Given the overall superiority of primary PCI over hospital-administered fibrinolysis, the former has emerged as the treatment of choice when the facilities and a high-volume, experienced operator and team are readily available and the coronary anatomy is suitable. Recent data suggest that outcomes with primary PCI remain superior to fibrinolysis as long as the added delay is less than 60 to 90 minutes. Longer delays in door-to-balloon time are associated with higher mortality, even after adjustment for differences in baseline characteristics. When PCI is not available or when the delay between presentation to a hospital and primary PCI is anticipated to be in excess of 90 minutes (which is more likely to occur in low-volume centers, in patients requiring transfer to a second facility or presenting between 6 PM and 8 AM), fibrinolytic therapy should be considered in patients who can be treated within 2 to 3 hours of symptom onset and who are not at high risk for intracranial hemorrhage. In such patients with fresh thrombus, fibrinolytic therapy is especially effective in opening an occluded infarct artery. Because the time to onset of treatment can be shortened by prehospital treatment, administration of fibrinolytic therapy in the ambulance, if available, is most appropriate in patients who present early. This may be followed by PCI to achieve maximal sustained patency of the infarct artery.

The Southwest German International Study in Acute Myocardial Infarction (SIAM) III trial suggests that even better outcomes might have been obtained had all patients receiving early fibrinolytic therapy undergone early angiography and revascularization, as transfer for stenting within 6 hours after fibrinolytic therapy was associated with a halving (25.6% versus 50.6%, P=0.001) of the composite outcome of death, reinfarction, ischemic events, and target lesion revascularization compared with a strategy of delayed elective coronary angiography at 2 weeks.

Because aging thrombi become more resistant to lysis, the efficacy of fibrinolytic therapy in establishing reperfusion and salvaging ischemic myocardium falls off with time from symptom onset, whereas the efficacy of PCI in achieving complete reperfusion and salvaging ischemic myocardium is far less time-dependent.11,19 In addition, patients who present later tend to be older, have more comorbidities, and are at increased risk for intracranial bleeding. Patients over the age of 75 years experience a 3-fold increase in death, reinfarction, or stroke after fibrinolysis compared with primary PCI.20 Thus, patients who cannot receive fibrinolytic therapy within 2 to 3 hours of symptom onset, but who can receive PCI within the next 90 minutes, should be offered this therapy, even if this entails transfer to another facility. Patients who present more than 2 to 3 hours after symptom onset with continued ischemic pain and/or ST-segment elevation, but who cannot be treated with PCI within the next 2 hours, should (if they have no contraindications) receive fibrinolytic therapy, as some myocardial salvage may still be achieved. These patients should be considered for immediate adjunctive PCI after fibrinolysis, particularly if they experience continued ischemic discomfort or ST elevation, recurrent ischemia, or have signs of left ventricular dysfunction, or later if they are not at low risk after noninvasive assessment.

Patients presenting more than approximately 6 hours after symptom onset, especially patients whose chest pain and ST elevation have subsided, will demonstrate only modest benefit from fibrinolysis but may be considered for coronary angiography as soon as feasible, as this approach permits risk stratification, allows for PCI when the anatomy is suitable, and identifies patients who would benefit from coronary artery bypass surgery. The window may be longer (up to 12 hours) in patients with preexisting coronary collaterals, persistent pain, and ST-segment elevation. The benefit of even later (>48 hours) opening of an occluded infarct artery is under investigation in the ongoing Occluded Artery Trial (OAT).

Autor: Dr. Ricardo Sarmiento, Jefe de Hemodinamia del Hospital Francés.

Fuente: SAC Sociedad Argentina de Cardiología - Comentarios Bibliográficos

Ultima actualizacion: 2 DE OCTUBRE DE 2003

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