Alterations in the initial portion of the signal-averaged QRS complex in acute myocardial infarction with ventricular tachycardia.

This study was designed to examine 2 hypotheses: that acute myocardial infarction (AMI) alters early cardiac activation measured by signal-averaging; and that the magnitude of abnormality of early activation may be greater in patients with post-AMI ventricular tachycardia (VT). We examined the root-mean square voltage amplitude in 10-ms intervals over the first 80-ms of the signal-averaged QRS complex. Data from 42 healthy volunteers were compared with those from 52 patients with previous AMI (24 anterior) but no VT and 46 post-AMI patients (33 anterior AMI) with recurrent sustained VT. Patients with VT differed from other post-AMI patients because of lower left ventricular ejection fraction, more frequent aneurysm formation and higher levels of ventricular ectopic activity. A significant decrease in initial voltage amplitude occurred at 30 to 40 ms after the beginning of the QRS in both anterior and inferior AMI patients compared with the normal group. A further significant decrease in initial amplitude occurred in VT patients both after anterior and inferior AMI. These differences persisted for the remainder of the 80-ms interval. These changes were weakly related to QRS duration (r = 0.45), ejection fraction (r = 0.50) and poorly correlated with the presence of Q waves on 12-lead electrocardiogram (r = 0.21). Direct endocardial catheter recordings performed in VT patients confirmed abnormalities of local septal activation after anterior and inferior AMI.(ABSTRACT TRUNCATED AT 250 WORDS)