Review: Prehospital thrombolysis for acute myocardial infarction decreases short term hospital mortality
Morrison LJ, Verbeek PR, McDonald AC, et al. Mortality and prehospital thrombolysis for acute myocardial infarction.
A meta.analysis. JAMA 2000 May 24/31;283:2686.92
QUESTION: Is prehospital thrombolysis more effective than inhospital thrombolysis for
decreasing short term mortality in patients with acute myocardial infarction (MI)?
Data sources
Studies were identified by searching Medline, Embase,
and Science Citation Index (1982 to 1999); Dissertation
Abstracts (1987 to 1999); and Current Contents (1994 to
1999) with the terms thrombolysis, thrombolysis
therapy, prehospital, and acute myocardial infarction
and with the Cochrane search strategy. Bibliographies of
relevant papers were searched, the US National
Institutes of Health web site was reviewed, and authors
and manufacturers of thrombolytic agents were
contacted.
Study selection
Randomised controlled trials were selected if they
compared prehospital with inhospital thrombolysis for
patients with MI and assessed all cause hospital mortality.
Data extraction
Data were extracted on trial quality, patient characteristics, provider and type of thrombolytic agent, time from
symptom onset to thrombolyis, and outcomes.
Main results
Six randomised controlled trials and three follow up
studies (6434 patients) met the selection criteria. Thrombolytic agents used included urokinase (one study), anistreplase (three studies), and recombinant tissue type
plasminogen activator (two studies). Providers of thrombolytic agents included paramedics (one study), general
practitioners (one study), and a mobile intensive care
unit (four studies). The type of thrombolytic agent used
and the level of provider training did not affect the outcomes. Prehospital thrombolysis was associated with a
shorter time from symptom onset to treatment (162 v
104 min, P = 0.007) and a lower risk for all cause hospital mortality (P = 0.03) than was inhospital thrombolysis
(table); prehospital and inhospital thrombolysis did not
differ for rates of one or two year mortality.
Prehospital v inhospital thrombolysis for acute myocardial infarction
Conclusion
Prehospital thrombolysis for acute myocardial infarction
decreases short term hospital mortality more than
inhospital thrombolysis.
COMMENTARY
Emergent reperfusion by thrombolytic or mechanical treatment has become the standard of care for patients with MI.
Numerous studies have shown the importance of early treatment. This finding has led to efforts to educate patients
about seeking earlier treatment and to reduce the time spent
in triage once patients have arrived at a treatment facility.
Given that time is an important variable, taking treatment
to the patient is one possible strategy for reducing mortality.
Studies of prehospital thrombolysis have shown nonstatistically significant reductions in inhospital mortality.
Morrison et al have done a careful review and meta.analysis
of randomised trials that compare prehospital and inhospital thrombolysis. They report a 16% relative risk reduction in
hospital mortality for patients treated with prehospital
rather than with inhospital thrombolytics. This reduction is
similar to that reported between differing thrombolytic regimens in the Global Utilization of Streptokinase and Tissue
Plasminogen Activator for Occluded Coronary Arteries
(GUSTO) trial.1
The meta-analysis by Morrison et al suggests that a strategy of prehospital thrombolysis has merit, but how to apply
this information in an era of changing thrombolytic agents
and increasing use of mechanical treatments is a difficult
problem. Where transport times are short, a prehospital
electrocardiogram could speed diagnosis. Treatment could
then be delivered quickly at the receiving facility. Where
transport times are longer, such as in rural areas, a prehospital strategy appears to be most useful. Delivery of treatment
in the field would require a coordinated emergency medical
system approach with well trained personnel, good
treatment protocols, and careful tracking of results.
Mirle A Kellett, Maine Medical Center, Portland, Maine,USA
- The GUSTO Investigators. An international randomized trial comparing four thrombolytic strategies for acute myocardial infarction. N Engl J Med 1993;329:673.82.
Dr L J Morrison, Division of Prehospital Care, Sunnybrook and Women's College, Health Science Centre, 2075 Bayview Avenue, Suite BG.20, Toronto, Ontario M4N 3M5, Canada
Email: phc.research@utoronto.ca
studentBMJ 2001;09:85-128 April ISSN 0966-6494
