Left Bundle-Branch Block and the ECG in Diagnosis of Acute Myocardial Infarction

To the Editor: Dr Shlipak and colleagues¹ assessed the value of our electrocardiographic (ECG) criteria to diagnose acute myocardial infarction (AMI) in patients with left bundle-branch block (BBB).² The conclusion, that our algorithm is worse than a "thrombolysis to all" approach, seems unsubstantiated. Idiosyncratic characteristics of the studied population may explain the low sensitivity of our ECG criteria, whereas assumptions in the decision analysis may have amplified the benefits of thrombolysis. The criterion standard selected for a study like this is critical. Elevations in creatine kinase-MB isoenzyme and troponin I (sensitive and specific markers of myocardial damage) cannot be equated to benefit from thrombolysis. The unusually high prevalence of AMI (56%) among patients with cardiac arrest in this series is unlikely to reflect acute coronary thrombosis.³ Unfortunately, the distribution of clinical presentations was not reported. Although the sensitivity remained low when only patients with chest pain were considered, the smaller sample size may have compromised the precision of the estimate.