EFFECTS OF SIMULATED LEFT-BUNDLE-BRANCH BLOCK ON QRST TIME-INTEGRAL VALUES OF 12-LEAD ELECTROCARDIOGRAMS IN PATIENTS WITH AND WITHOUT PRIOR ANTERIOR WALL MYOCARDIAL-INFARCTION

The effects of right ventricular pacing, which simulated left bundle branch block (BBB), on QRST time-integral values of 12-lead electrocardiograms (ECGs) were examined, and the clinical usefulness of QRST values for, estimating the severity of left ventricular wall motion abnormalities due to a prior anterior wall myocardial infarction (MI) in the setting of left BBB were evaluated. Digitized ECGs were recorded during normal sinus rhythm and simulated left BBB in 38 patients (24 with and 14 without prior anterior wall MI). QRST values were calculated in each lead point of 12-lead ECGs. Data from 608 normal subjects were used as control values; the mean +/- 2 SD of these values was regarded as the normal range. The parameter SIGMADE was defined as the sum of the differences between the normal mean QRST value and the QRST values of a given patient in leads where the QRST value was less than the normal range. The correlation coefficient of SIGMADE for the 2 activation sequences was highly significant. Although small but significant changes were seen in QRST values in leads I, II, III, aVR, aVF and V1 during simulated left BBB, left precordial leads showed no significant changes in QRST values. A criterion of SIGMADE >40 mV . ms for detecting an anterior wall MI showed a sensitivity of 88%, a specificity of 93%, and a diagnostic accuracy of 89%. The SIGMADE was significantly (p < 0.001) correlated with the asynergy index calculated from left ventriculograms. The results show that simulated left BBB has little effect on QRST values of 12-lead ECGs, especially in left precordial leads, and that the QRST values may provide clinically useful information for detecting the presence of MI and estimating the severity of left ventricular wall motion abnormalities in patients with a prior anterior wall MI in the setting of left BBB.