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Prehospital thrombolysis for MI

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The goal of starting thrombolysis early after a heart attack is one known to most people through television medical dramas. Out of the ambulance, into the emergency room, and get some lines up. A new meta-analysis [1] tells us that additional benefit comes from beginning thrombolytic therapy before the patient gets to hospital.

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The analysis had an extensive search strategy in a number of electronic databases, and included reviewing any grants that may have been given for this type of research in the USA. Authors and manufacturers were also contacted.

To be included a study had to be a randomised controlled trial of prehospital with in-hospital thrombolysis in acute myocardial infarction. The main outcome was all-cause hospital mortality.

Results


Six studies made it into the final analysis, with 6434 patients. Most did not have concealment of randomisation, and outcomes were not assessed blind. Three different thrombolytic agents (anistereplase, TPA and urokinase) were given in mobile intensive care units (four trials) or by GPs (1) or paramedics (1). Diagnosis of infarction varied between clinical impression and detailed criteria including ECG changes. One large trial had over three-quarters of the patients, and three trials had fewer than 150 patients in total.

Trials reported the time from onset of symptoms to thrombolysis (Figure 1). The time between onset of symptoms and start of thrombolysis was about 60 minutes shorter when thrombolysis was started before hospital admission. Over all, 324 of 3167 patients (10.2%) died in hospital when thrombolysis was begun in hospital. When thrombolysis was begun before hospital admission 280 of 3257 patients (8.6%) of patients died in hospital (Figure 2). This meant that for every 61 patients who had thrombolysis begun before hospital admission, one fewer would die than if thrombolysis had begun in hospital. The NNT was 61 (95% CI 33 to 488).

Figure 1: Mean time between symptoms and start of thrombolysis

Figure 2: Percentage of patients dying in hospital

 


Sensitivity analysis showed that results were similar irrespective of trial quality or provider of thrombolysis.

Comment


As we have come to expect from the folks at McMaster, this is a splendid review performed to high standards, and it shows a small but significant benefit from starting thrombolysis before patients get to hospital. This is likely to be particularly beneficial in circumstances outside cities, where the delay before admission to hospital may be delayed because of distance or circumstance.

Reference:

  1. LJ Morrison et al. Mortality and prehospital thrombolysis for acute myocardial infarction. JAMA 2000 283: 2686-2692.
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