A critique of the new ST-segment criteria for the diagnosis of acute myocardial infarction in patients with left bundle-branch block

Background: Recently, electrocardiogram (ECG) criteria have been proposed for the diagnosis of acute myocardial infarction (AMI) in the presence of left bundle-branch block (LBBB). However, clinical experience indicates that such ECG changes indicative of AMI are occasionally noted in clinically stable patients with LBBB, raising concerns about the specificity of the proposed criteria. Hypothesis: The aim of this study was to evaluate the frequency of ST-segment abnormalities suggestive of AMI in ambulatory patients with cardiovascular disease and chronic LBBB, who did not have an AMI In addition, the ECG determinants of such ST-segment abnormalities were sought. Methods: The files of all (4,193) patients followed in the outpatient cardiology clinic were reviewed to identify patients with LBBB. Electrocardiograms of these patients were evaluated as to the duration of the QRS complex, frontal QRS axis, amplitude of QRS in leads V-1-V-3, and the presence and magnitude of ST-segment depression (-ST) in leads V-1-V-3, and ST-segment elevation (+ST) in leads with predominantly positive or negative QRS complexes. Correlations of these ECG variables were carried out. Results: In 124 patients with LBBB only 1 patient with -ST of 1 mm in leads V-1-V-3, and 1 patient with +ST of 1 mm in a predominantly positive ECG lead were found; the latter patient also had +ST of 6 mm in V-3. Nine patients were detected with greater than or equal to5 mm +ST in at least one ECG lead with predominantly negative QRS complex. Regression analysis of amplitude of +STs on corresponding QRS amplitudes in leads V-1-V-3 yielded Rs of 0.69,0.68, and 0.69, all with a p value of 0.00005. A similar analysis of the amplitudes of +STs greater than or equal to5 mm with the corresponding QRSs yielded an R=0.76 and a p value of 0.0018. Conclusions: Thus, recently proposed ST-segment criteria for the diagnosis of AMI in patients with LBBB are appropriate. However, stable greater than or equal to5 mm +STs are occasionally found in leads with predominantly negative QRS complexes, particularly of large amplitude (mean value 46.0, range [28.0-71.0] mm) in the absence of AMI. In such patients presenting with symptoms suggestive of AMI, further non-ECG confirmation of probable underlying AMI should be sought.