Autonomic Manipulation Influences Both Temporal and Frequency Analyses of Late Potentials

Previous studies of late potentials have not standardized the autonomic milieu at the time of testing. We studied the effects of autonomic manipulation in seven patients with previous Q wave myocardial infarction. Late potentials were evaluated using standard temporal (TD) and spectral temporal mapping techniques (STM) in the drug free state, and during separate intravenous administration of each of the following: isoproterenol, esmolol, and atropine. Isoproterenol was nitrated to achieve a heart rate of 130% of baseline. Esmolol was infused at a rate of 250 μg/kg per minute, after a loading dose of 500 μg/kg. Atropine was given as a 2-mg bolus. In addition, five patients who received no drug infusions acted as controls, undergoing four serial signal-averaging studies in the baseline state: a "baseline" study, and then three additional studies at time intervals similar to those incurred by the study patients. Therefore, a total of 21 TD and 21 STM tests were done in the study group seven patients; three drugs per patient) during the drug infusions, and 15 TD and 15 STM tests were done in the control group (five patients; three "nonbaseline" tests per patient). A change normal to abnormal, or vice versa) in TD during a drug infusion occurred in 24% of the tests. No such change occurred in the control group (P < 0.01). A change in STM during a drug infusion occurred in 38% of tests, versus 13% of tests in the control group (P = 0.14). Overall, six of seven patients had a change in TD and/or STM diagnosis with infusion of one or more of the study drugs. Optimal clinical use of late potentials may require a standardized autonomic environment.