Can the MAP Technique Be Applied to Detect Delayed Afterdepolarization? Electrophysiologic and Pharmacologic Evidence

The purpose of this study was to assess whether the monophasic action potentials (MAPs) technique can be applied to detect delayed afterdepolarizations (DADs). The canine isolated, blood-perfused ventricular septum preparation was used to obtain stable MAP signals (n = 8). The preparation was electrically driven by trains of 15 stimuli at each cycle length of 600-300 ms under the monitoring of MAP and papillary muscle contraction. In a basal condition, neither DADs nor premature ventricular contractions (PVCs) were induced by the train stimulation, whereas the coupling interval between electrograms of the last driven contraction and the first spontaneously developed contraction was prolonged by shortening the pacing cycle length. Then 40-45 microg of ouabain was intravenously administered into the blood-donor dog. Both DADs and PVCs were induced in all preparations by the pacing protocol 10-15 min after the ouabain injection; however, PVCs did not occur spontaneously. Small aftercontractions also were detected during the electrical pacing in four preparations. By shortening the pacing cycle length, the DADs were enhanced, the coupling interval was shortened, and the number of PVCs increased. After the administration of ryanodine, verapamil, tetrodotoxin, or lidocaine (n = 4--6), the small aftercontractions disappeared, the DADs attenuated, the coupling interval was prolonged, and the number of PVCs decreased. These observations suggest that PVCs observed in this model may be derived from the DAD-related triggered activity, and moreover, show the feasibility of recording DADs and triggered activity by the MAP technique.