Predictive value of q waves in inferior leads for the diagnosis of old inferior wall myocardial infarction

Abstract

Background: A diagnosis of an old Inferior Wall Myocardial Infarction (IMI), on a routinely performed Electrocardiogram (ECG) often leads to further consultations and imaging studies. The aim of this study was to assess the predictive value of Q waves in inferior leads, alone or in combination with repolarization abnormalities, for the diagnosis of inferior wall myocardial infarction confirmed by imaging studies. Methods: Fifty-six patients, in whom computerized interpretation of the electrocardiogram resulted in the diagnosis of inferior wall myocardial infarction, and in whom imaging studies were also available, were included in this study. Electrocardiograms were performed using the GE MACHD 5500. Electrocardiograms were interpreted using the MUSE GE system. Echocardiograms and nuclear medicine cardiac imaging were performed and interpreted using standard equipment and techniques. S AS 9.3 software (SAS Institute, Inc., Cary, North Carolina) was used to calculate 95% exact binomial confidence intervals (CI) for the population PPVs. Results: Computerized interpretation of the ECGs leading to the diagnosis of old inferior wall myocardial infarction when compared with inferior wall myocardial infarction confirmed by imaging studies, had a positive predictive value of 52.78%. Adding the criteria of Q waves wider than 0.04 ms, using manual interpretation of ECG, increased the positive predictive value of the test to 80%. However, the presence of ST changes and/or negative or isoelectric T waves, in the presence of diagnostic Q waves in the inferior leads, increased the positive predictive value to 92%. Conclusion: These results suggest that the computerized interpretation of ECG results in a high rate of false positive readings of old inferior myocardial infarction. This may result in overutilization of imaging modalities. Presence of diagnostic Q waves in inferior leads, if accompanied by repolarization abnormalities, improves the accuracy of the electrocardiogram for the diagnosis of inferior wall myocardial infarction..