The impact of pre-hospital thrombolytic treatment on re-infarction rates: Analysis of the Myocardial Infarction National Audit project (MINAP) Dr Simon Horne Specialist Registrar Emergency Medicine Torbay Hospital

Background to the study Pre-hospital thrombolysis allows earlier treatment of Acute Myocardial Infarction (AMI). This in turn improves outcome. Ambulance systems allow real time observation of the pre-hospital ECG in the Emergency department. Anecdotal evidence suggested a high rate of re- infarction after pre-hospital treatment.

What is re-infarction? “Ischaemic pain or other symptoms consistent with acute cardiac ischaemia …accompanied by new electrocardiographic changes (elevation or depression of the ST segment or T waves changes) in the territory of the initial event”

Why re-infarction is important

Study hypothesis That pre-hospital thrombolysis has a higher rate of re-infarction than in-hospital thrombolysis.

Methods Use of the MINAP database of 35,356 patients thrombolysed in Comparison of pre-hospital and in-hospital groups to identify differences in baseline characteristics and re-infarction rate. Use of multivariate linear regression to identify factors predictive of re-infarction.

Baseline characteristics

Re-infarction rate by agent * * * p=0.001 † † † p=0.005

Re-infarction rate by time from administration to time of arrival at hospital † † † p=0.001

Predictors of re-infarction For Tenecteplase: Weight OR 1.67 (95%CI ) Pre-hospital OR 1.44 (95%CI ) Previous AMIOR 1.23 (95%CI ) For Reteplase: Previous AMIOR 2.74 (95%CI ) CRFOR 2.6 (95%CI )

Why might this happen? Chance? A difference between the groups that we have no data about? Anticoagulation?

Limitations of the study Use of a dataset for a specific question for which it was not designed. No randomisation to reduce bias. Data quality is an issue. No direct evidence of cause, only effect. but Complete picture for England and Wales. Robust evidence that something about pre- hospital thrombolysis is suboptimal.

Conclusions Pre-hospital thrombolysis with Tenecteplase is associated with an increased risk of re- infarction. Re-infarction more than doubles mortality from AMI. As time from treatment to hospital increases, so does the rate of re-infarction. The anticoagulation regimen is an obvious difference between the groups that might explain the results.