Time to Reperfusion

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Acute thrombotic coronary occlusion results in a front of ischemia, leading eventually to tissue necrosis (5). The resulting injury depends on the duration of the insult, the rapidity and completeness of reperfusion, presence and extent of collateral circulation, and destruction of microvasculature. Boersma et al. have shown in a systematic evaluation of fibrinolytic therapy that when applied within the first hour of symptom onset, 65 lives/1000 patients treated are saved, as compared to only 29 lives saved, when given 3 h or more from infarct onset (6) (Fig. 1). Similar data from the Gruppo Italiano per lo studio della sopravvivenza nell'Infarto Micardico (GISSI)-I trial (7) and studies of prehospital thrombolytic administration (8,9) have focused our attention on the need for very early therapy for acute MI. Regrettably, the same studies showed that only a small fraction (3-5%) of patients present within this "golden hour". In contrast, mechanical reperfusion restores flow almost simultaneously with its successful application. Although earlier mechanical reperfusion is also very desirable, a number of observations suggest that the rather direct relationship between survival and time to reperfusion existent for fibrinolysis applies less stringently in the case of angioplasty. Consistently, there is a 30-60 min additional delay to onset of therapy when comparing angioplasty with fibrinolysis. Cannon et al. (10) examined this complex interaction in the National Registry of Myocardial Infarction (NRMI) II. While there was no significant correlation between time from symptom onset to balloon inflation (total ischemia time) and mortality, there was a direct and steep dependency between hospital delay to angioplasty and mortality, particularly beyond 2 h of delay (Fig. 2). The first statement may not accurately account for intermittent arterial patency, while the latter is confounded by sick

Fig. 2. Adjusted odds ratio of death by time from symptom onset (A) and from hospital arrival (B) to first balloon inflation. Adapted from ref. 10.

patients in cardiogenic shock requiring stabilization. Nevertheless, they point to the fact that more reliable reperfusion may atone for a slightly longer delay. Indeed, similar results were obtained from other clinical trials (11,12). Recently, investigators in the Stent versus Thrombolysis for Occluded Coronary Arteries in Patients with Acute Myocardial Infarction (STOP AMI) trial demonstrated that myocardial salvage index was significantly higher for angioplasty than for lysis at any interval from symptom onset and, particularly so, after the initial 3 h (13) (Fig. 3).

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