Patients with acute myocardial infarction (AMI), for which reperfusion therapies may be appropriate, are managed within this module.

An AMI for which reperfusion therapies may be appropriate is defined by the following:

• Clinical history of ischemic- or infarction-type symptoms
• Diagnostic electrocardiogram (ECG) findings of new or old LBBB or ongoing ST-segment elevation in two or more contiguous leads (i.e., 0.2 mV or more in leads V1-V3, or 0.1 mV or more in other leads)

Patients are presumed to have an acute ST-Elevation myocardial infarction (STEMI) on the basis of typical ECG findings of LBBB or "new or presumed new ST segment elevation at the J point in two or more contiguous leads with the cut-off points ³ 0.2 mV in leads V1, V2, or V3 or ³ 0.1 mV in other leads (contiguity in the frontal plane is defined by the lead sequence aVL, I, inverted aVR, II, aVF, III)" (ESC/ACC, 2000). Patients presenting with symptoms suggestive of a MI and LBBB, whether new or old, should be considered for reperfusion therapy. In the Fibrinolytic Therapy Trialists' Collaborative Group (FTT, 1994) analysis of nine thrombolytic trials, patients presenting with any bundle branch block (BBB) (i.e., right or left, or new or old) had the highest risk of death when compared to all other ECG criteria. Though thrombolysis for patients with BBB had the most benefit compared to all other ECG criteria, reducing mortality from 23.6% in the placebo group to 18.7% in the treatment group, this group represented only 4% of all patients in the trials. Despite thrombolytic treatment, BBB was also associated with the highest mortality. In an analysis of the TAMI-9 and GUSTO-I, new onset BBB was associated with lower ejection fractions (EF), left anterior descending artery infarctions, and higher peak creatine phosphokinase (CK) levels. Thrombolytic therapy reduced the overall mortality rate in this group, but the presence of persistent BBB predicted higher mortality rates, despite thrombolysis (Newby, Pisano et al., 1996).

The European Society of Cardiology and the American College of Cardiology's (ESC/ACC) redefinition of myocardial infarction requires a typical rise and fall of cardiac enzymes as a criterion for the definition of a MI; however, the delay in obtaining test results for these cardiac markers, as well as lack of sensitivity when patients present within four hours of the onset of symptoms, make use of this criterion impractical for assessing an AMI on initial presentation. The SMARTT trial evaluated the use of early cardiac serum markers on the use of thrombolytic therapy and found that the use of early cardiac serum markers had no effect on the use of thrombolytic therapy for patients presenting with an AMI (Gibler et al., 2000).

Evaluation of both the FTT (1994) and TIMI IIIB (1994) showed no mortality benefit in patients treated with thrombolytic agents in the setting of an AMI and ST-segment depression. Patients with ST-depression should be referred to Module B for further treatment.