Clinical study of late potentials. Serial changes of late potentials in relation to ventricular arrhythmias and hemodynamic findings in acute myocardial infarction.

Late potentials (LPs) recorded using the signal averaging technique were studied sequentially in 12 cases with acute myocardial infarction (AMI) in order to clarify how LPs develop in relation to ventricular arrhythmias (VA) in this disorder. Within 7 days after the onset of AMI there were no significant differences between LP durations with and without VA, and the overall mean value was relatively short (15.9 +/- 5.0 msec). On the 14th day, these cases were clearly divided into two groups according to LP duration. The group with LP duration over 20 msec (n = 5, average: 24.3 +/- 1.5 msec) exhibited a higher VA score and the other group with a shorter LP duration (n = 7, average: 15.0 +/- 2.1 msec) had a lower VA score (4.3 +/- 0.9 vs 0.6 +/- 0.5, p less than 0.001). This tendency was observed even in the late phase, and data such as peak CPK, cardiac index and mean pulmonary capillary pressure obtained in the acute phase could not predict this separation. In conclusion, LPs appear slightly later following the onset of AMI and correspond with the appearance of VA in the late phase; thus, LPs are useful for the prediction of VA in the course of AMI.