Context: Recently, an algorithm based on the electrocardiogram (ECG) was reported to predict myocardial infarction (MI) in patients with left bundle- branch block (LBBB), but the clinical impact of this testing strategy is unknown. Objective: To determine the diagnostic test characteristics and clinical utility of this ECG algorithm for patients with suspected MI. Design: Retrospective cohort study to which an algorithm was applied, followed by decision analysis regarding thrombolysis made with or without the algorithm. Setting: University emergency department, 1994 through 1997. Patients Eighty-three patients with LBBB who presented 103 times with symptoms suggestive of MI. Main Outcome Measures: Myocardial infarction determined by serial cardiac enzyme analyses and stroke-free survival. Results: Of 9 ECG findings assessed, none effectively distinguished the 30% of patients with MI from those with other diagnoses. The ECG algorithm indicated positive findings in only 3% of presentations and had a sensitivity of 10% (95% confidence interval, 2%-26%). The decision analysis showed that among 1000 patients with LBBB and chest pain, 929 would survive without major stroke if all received thrombolysis compared with 918 if the ECG algorithm was used as a screening test. Conclusions: The ECG is a poor predictor of MI in a community-based cohort of patients with LBBB and acute cardiopulmonary symptoms. Acute thrombolytic therapy should be considered for all patients with LBBB who have symptoms consistent with MI.
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