956-119 Inferior Wall Myocardial Infarction and Thrombolytic Therapy: An Appraisal of Clinical Heterogeneity and Indications for Treatment

Abstract

Clinical trials to determine the efficacy of thrombolytic therapy trials consider all patients with acute inferior myocardial infarction (IMI) as a single group, but these patients have heterogeneous clinical characteristics. Stratification of IMI patients by the amount of myocardium at risk and the time to treatment should clarify the precise indications for thrombolytic therapy. This study is an independent secondary analysis of the TIMI II patient data available through the NHLBI. Clinical features were used to identify IMI subgroups in the TIMI II trial characterized by increased myocardium at risk. There were 861 patients with IMI who had one or more of the following markers for myocardium at risk: anterior ST depression, hypotension defined as a systolic blood pressure < 100 mmHg, or advanced AV block. There were 455 patients with IMI who did not have any markers of increased myocardium at risk. The subgroups for each marker and the group without any marker were then stratified by time to thrombolysis and their outcomes were compared to historical controls with hypothesis tests and confidence intervals. Patients with IMI plus anterior ST depression, hypotension, or AV block who received thrombolysis had a highly statistically significant decre,1se in mortality (p < 0.001) compared to historical controls. Patients with IMI plus hypotension or AV block had a significant decrease in mortality only up to 3 hours from onset of symptoms (p < 0.05). In patients with simple 1MI, an insignificant relative reduction in mortality of 15.4% was seen from a baseline mortality of 2.5%. Consequently, thrombolytic therapy cannot be justified for all patients with IMI, but it is clearly indicated for IMI with anterior ST depression, advanced AV block, and hypotension. The decrease in mortality for patients with hypotension or AV block declines steeply over the first 3 hours. IMI with anterior or lateral ST elevation, right ventricular infarction, or new bundle-branch block is hypothesized to have the same benefit but could not be tested because the data was not available in the TIMI II database. To demonstrate significance of the relative reduction in mortality for patients with simple IMI would require 32,220 patients. For the individual patient with a simple inferior myocardial infarction, the essentially immaterial benefit of 15.4% relative reduction in mortality from a baseline mortality of 2.5% may not outweigh the risk of a hemorrhagic complication of therapy. In conclusion, IMI patients should be considered on an individual basis, with consideration given to the amount of myocardium at risk and the time to treatment.