Electrocardiographic Diagnosis of Evolving Acute Myocardial Infarction in the Presence of Left Bundle-Branch Block

Background. The presence of left bundlebranch block on the electrocardiogram may conceal the changes of acute myocardial infarction, which can delay both its recognition and treatment. We tested electrocardiographic criteria for the diagnosis of acute infarction in the presence of left bundle-branch block. Methods. The base-line electrocardiograms of patients enrolled in the GUSTO-1 (Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries) trial who had left bundle-branch block and acute myocardial infarction confirmed by enzyme studies were blindly compared with the electrocardiograms of control patients who had chronic coronary artery disease and left bundle-branch block. The electrocardiographic criteria for the diagnosis of infarction were then tested in an independent sample of patients presenting with acute chest pain and left bundle-branch block. Results. Of 26,003 North American patients, 131 (0.5 percent) with acute myocardial infarction had left bundlebranch block. The three electrocardiographic criteria with independent value in the diagnosis of acute infarction in these patients were ST-segment elevation of 1 mm or more that was concordant with (in the same direction as) the QRS complex; ST-segment depression of 1 mm or more in lead V 1 , V 2 , or V 3 ; and ST-segment elevation of 5 mm or more that was discordant with (in the opposite direction from) the QRS complex. We used these three criteria to develop a scoring system (0 to 5), which allowed a highly specific diagnosis of acute myocardial infarction to be made. Conclusions. We developed and validated a clinical prediction rule based on a set of electrocardiographic criteria for the diagnosis of acute myocardial infarction in patients with chest pain and left bundle-branch block. The use of these criteria, which are based on simple STsegment changes, may help identify patients with acute myocardial infarction, who can then receive appropriate treatment. (N Engl J Med 1996;334:481-7.)  1996, Massachusetts Medical Society. From the Cleveland Clinic Foundation, Cleveland (E.B.S., S.L.P., D.A.U., E.J.T.); the Fundación Favaloro, Buenos Aires, Argentina (A.B.); and Duke University Medical Center, Durham, N.C. (K.B.G., R.M.C., G.S.W.). Address reprint requests to Dr. Sgarbossa at the Department of Cardiology, Desk M-24, Cleveland Clinic Foundation, Cleveland, OH 44195. Supported by grants from Bayer, Genentech, CIBA–Corning, ICI Pharmaceuticals, and Sanofi Pharmaceuticals. T HE optimal use of coronary reperfusion therapies relies on a rapid diagnosis of evolving myocardial infarction. 1,2 For most patients presenting with cardiac chest pain, the electrocardiogram is a powerful aid in diagnosing the cause of the pain and selecting the appropriate therapy. 2 In patients who present with concomitant left bundle-branch block, however, the electrocardiographic manifestations of acute myocardial injury may be masked. During the past five decades, several electrocardiographic signs have been proposed to aid in the diagnosis of infarction in such patients, but because of methodologic limitations, 3-9 none of these signs have gained widespread acceptance. Many physicians believe that acute myocardial injury cannot be detected accurately in patients with left bundle-branch block. 10 We examined the value of the standard electrocardiogram for the diagnosis of acute myocardial infarction in the presence of left bundle-branch block in a large population of patients.