[Prehospital thrombolytic therapy of acute myocardial infarct]

The extent of myocardial damage occurring during acute myocardial infarction is time dependent, and there is abundant evidence from most clinical trials that mortality reduction is greatest in patients treated early with thrombolytic agents, although beneficial effects have been shown with treatment initiated up to 12 hours after onset of symptoms. This temporal dependence of benefit was most clearly seen with the 47% mortality reduction obtained with streptokinase given within the first hour in the GISSI-1 trial (Table 1). The process of infarction may be completely aborted if reperfusion is initiated within 30 minutes after symptom onset. Current approaches designed to reduce the time delay between onset of symptoms and the initiation of thrombolytic treatment include increasing public awareness of the need to seek prompt medical attention in the event of chest pain, reducing in-hospital delays in initiation of thrombolytic therapy, and administration of thrombolytic agents in the prehospital setting. Since the first paper on prehospital thrombolysis by Koren et al. in 1985 there have been numerous studies published, including several randomized trials comparing prehospital and in-hospital initiation of thrombolytic therapy (Table 2). In randomized studies patients received in the pre-hospital phase either a bolus or infusion with the thrombolytic agent followed by placebo after hospital admission, or placebo when first seen outside the hospital, followed by the thrombolytic agent after arrival at the hospital. This was performed in a double-blind fashion in some of the trials. Some of the studies on prehospital thrombolysis have focused only on feasibility and safety, others on time gain, differences in ejection fraction and mortality benefit. Almost all have conclusively shown the practicability and safety of patient selection and administration of the thrombolytic agent. This positive result was observed in different organizational types of the emergency system: In the Myocardial Infarction Triage and Intervention trial (MITI) patients with chest pain were screened by paramedics using a checklist of clinical inclusion and exclusion criteria. The paramedics then obtained a computer-interpreted ECG which was transmitted to the emergency department in the hospital where a physician made the decision on the form of treatment. The thrombolytic agent was then administered by the paramedic. In the European Myocardial Infarction Project (EMIP) an emergency physician was personally present and responsible in the prehospital setting, whereas in the Grampian Region Early Anistreplase Trial (GREAT) general practitioners made the decision for enrolling the patient.