LABORATORY INVESTIGATION ELECTROPHYSIOLOGY Recording of diastolic slope from the junctional area in dogs with junctional rhythm

Stable junctional rhythm was induced in 14 of 25 anesthetized dogs by exclufsion of the sinus node and surrounding atrial tissue. In 12 of the 14 dogs diastolic slope was recorded through a unipolar lead consisting of a terminal of a plunge or catheter electrode placed in the His bundle area coupled with an indifferent superior vena caval electrode. Reversed polarity, high-gain amplification (0.1 mV/cm), and low-pass filters (0.1 to 50 Hz) were used for the unipolar recording. The diastolic slope (0.15 + 0.07 mV/sec) was recorded from a localized area close to the His bundle and preceded the bipolar His bundle deflection. Overdrive atrial stimulation was followed by slowing of the junctional rate and decrease in the diastolic slope. A strong negative correlation (r values from -.78 to -.95) was found between the junctional cycle lengths and the diastolic slopes after atrial pacing. Isoproterenol infusion increased the junctional rate and the diastolic slope, whereas vagal stimulation and verapamil injection decreased them. The effects of verapamil were partly reversed by CaCl2 injection. The responses of the diastolic slope to overdrive pacing, vagal stimulation, and isoproterenol suggest that the deflection is indeed due to membrane current responsible for phase 4 depolarization. The responses of the junctional rhythm and the diastolic slope to verapamil and CaCl2 suggest that AV nodal automaticity is responsible for the rhythm. Clinical application of this recording technique should help in the identification and characterization of automatic junctional rhythm. Circulation 68, No. 3, 636-643, 1983. DIASTOLIC SLOPES that accurately reflect the phase 4 depolarization of the pacemaker cells have been recorded extracellularly from the sinus node and ectopic atrial foci in dogs and humans.1-3 These diastolic slopes can be used as a marker of the activity of the pacemaker, both normal and abnormal. Thus, recording of these diastolic slopes could be useful in the identification of abnormal pacemakers as a cause of the cardiac arrhythmia and in the study of the characteristics of the pacemakers responsible for the arrhythmia. In this paper we describe the recording of diastolic slope in the junctional area in dogs with junctional rhythm and the effects of various interventions on this slope and the rate of the rhythm. Our results provide a method of recording this slope and of verification that it is indeed due to membrane current responsible for From the Department of Cardiology, U.S. Public Health Service Hospital, Staten Island. Supported in part by Bureau of Medical Services and Public Health Service Research Support, Project STI 80-33. Address for correspondence: Robert J. Hariman, M.D., Department of Cardiology, VA Medical Center, Brooklyn, NY 11209. Received Jan. 25, 1983; revision accepted April 28, 1983. Presented before the 30th and 31st Annual Scientific Session of the American College of Cardiology, 1981, San Francisco, CA, and 1982, Atlanta, GA. 636 phase 4 depolarization of the cardiac pacemaker in the junctional area.