Clinical outcomes according to time to treatment.
Twenty years ago, pathophysiologic studies showed that myocardial salvage in acute myocardial infarction depends on early intervention. A meta-analysis of the largest thrombolytic trials showed 1.6 lives saved/1000 treated for each hour closer to symptom onset, and that patients treated in the first hour have a much higher survival rate. The MITI trial found a seven-fold decrease in mortality in patients treated within 70 min of symptom onset. The GUSTO study showed similar results, except that during the first hour mortality was actually higher than in the second hour. In contrast, studies have found that while little survival benefit accrues from treatment after a 12 h delay, significant benefit is achieved by treatment between 6 and 12 h from symptom onset. Thus, mechanisms other than myocardial salvage are at work. A GUSTO substudy demonstrated considerable in-hospital delays in attaining electrocardiographic readings, in deciding on the course of therapy, and most of all in the time to infuse the drug. Other delays in both presentation and treatment are related to patient characteristics such as age, gender, diabetes, and Killip class. The medical community cannot control delays in presentation, but it has been able to reduce in-hospital delays, with resultant benefits in morbidity as well as mortality. At the end of the day, reducing delay outweighs the choice of thrombolytic agent.
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