title: Late thrombolytic therapy: mechanism of benefit and potential risk among patients treated beyond 6 hours.
abstract: BACKGROUND
  Thrombolytic therapy is the treatment of choice for many patients with myocardial infarction, particularly those presenting to the hospital within 6 hours from symptom onset. Although prompt treatment promises to provide the greatest overall benefit, delayed thrombolysis (possibly beyond a time when myocardial salvage is achieved) may also have a role in current clinical practice.
  
  
  METHODS
  A review of the English-language literature was conducted by MEDLINE search. Pertinent references were found as far back as 1912.
  
  
  RESULTS
  Results of several nonrandomized clinical studies and one recently completed randomized study (the Late Assessment of Thrombolytic therapy Efficacy [LATE]) suggest that thrombolytic therapy may be beneficial up to 12 hours from the onset of symptoms. The mechanisms of benefit are poorly defined, but they may include myocardial salvage, reduced early infarct zone expansion, improved healing, and decreased ventricular irritability. These mechanisms are not necessarily exclusive of one another. An increased risk of myocardial rupture and thromboembolism may be incurred, limiting the usefulness of treatment with further delay.
  
  
  CONCLUSIONS
  Delayed thrombolysis (up to and possibly beyond 12 hours from symptom onset in certain patient subgroups) reduces patient mortality. Despite increasing support, however, many patients, even those seeking medical treatment within 6 hours, are not being given thrombolytic therapy. Further investigation into this area must be undertaken. The Benefits of Late Thrombolysis (BOLT) study should provide much needed information.
authors.affiliation: Thrombosis Research Center, University of Massachusetts Medical School, Worcester 01655.
authors.forename: R C
authors.initials: RC
authors.lastname: Becker
mesh_terms: D002986:Clinical Trials as Topic; D017023:Coronary Angiography / Q000187:drug effects; D004334:Drug Administration Schedule; D005343:Fibrinolytic Agents / Q000008:administration & dosage; D006801:Humans; D009203:Myocardial Infarction / Q000000981:diagnostic imaging / Q000188:drug therapy* / Q000401:mortality; D012307:Risk Factors; D015996:Survival Rate; D015912:Thrombolytic Therapy
chemical_list: D005343:Fibrinolytic Agents