Prehospital thrombolytic therapy in acute myocardial infarction

Abstract

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 h after onset of symptoms. All studies on prehospital thrombolysis have conclusively shown the practicability and safety of patient selection and administration of the thrombolytic agent. The accuracy of diagnosis in the prehospital setting was comparable to trials of in-hospital thrombolysis, e.g., in the Myocardial Infarction Triage and Intervention Project (MITI) 98% of the patients enrolled had subsequent evidence of acute myocardial infarction. With regard to time savings, all randomized studies showed positive results. The smallest time gain was observed in the MITI trial: prehospital-treated patients received thrombolytic therapy an average of 33 min earlier than those treated in hospital. In the European Myocardial Infarction Project (EMIP) the difference in time between prehospital and hospital treatment was a median of 55 min. However, none of these trials was able to show a significant short-term mortality difference between the two groups. Only a meta analysis of five randomized studies with a combined median time gain of about 60 min showed a significant 17% reduction in short-term mortality for patients who received thrombolytic therapy in the prehospital phase. In the Grampian Region Early Anistreplase Trial (GREAT), a study performed in a more rural area than other studies, the time gain by prehospital initiation of thrombolysis was a median of 130 min. GREAT was the only study to date reporting a significant mortality benefit for prehospital-treated patients after 3 months and 1 year. In conclusion, prehospital thrombolysis is feasible and safe. Patients with acute myocardial infarction can be correctly identified and treated with thrombolytic agents in the prehospital setting with the same rate of complications as expected for in-hospital thrombolysis, provided basic resuscitation equipment including a defibrillator is available. The results of randomized studies comparing the results of prehospital and in-hospital thrombolysis seem to justify the prehospital institution of thrombolytic therapy, especially in rural areas where transport times to the hospital are long and the expected time gain is largest. The choice of the thrombolytic agent seems to be of minor importance and should follow prehospital practicability (bolus injection) and costs. Aspirin should be given to all prehospital patients with suspected myocardial infarction regardless of thrombolytic therapy.