The Cardioelectric Field on the Pig Body Surface during Initial Atrial Activity

Abstract

In humans, the electrical activity of the sinoatrial node arises prior to the beginning of the P-wave recording in the ECG [1]. During the investigation of the intramural initial atrial activity, the period of electrocardiographic "silence" in the ECG in superficial leads was found in sheep [2,3]. A question arises of the regularities of the reflection of the electric processes in the atria on the body surface at the initial stages of depolarization and not reflected in the ECG in the standard leads.The body surface cardioelectric field was investigated in 14 three-month-old male and female pigs (Landras and Large White breeds) using an electrocardiotopographic system developed at the Institute of Physiology, Komi Science Center, Ural Division, Russian Academy of Sciences. Unipolar cardioelectric potentials were simultaneously recorded from 64 or 128 subcutaneous needle electrodes uniformly distributed over the torso surface (from the base of ears to the last rib) of an anaesthetized pig (sodium thiopental, 100 mg/kg) lying on its back. The ECG in the sagittal bipolar body surface leads (according to M.P. Roshchevsky, IIS) was recorded synchronously with the cardioelectrical potentials. All data are represented as an arithmetic mean ± SD.The cardioelectric field on the body surface was formed on the body surface prior to the occurrence of the atrial P IIS -wave in the ECG in the II sagittal lead. In this period ( 123 ± 14 ms before the R IIS -wave peak), accepted as a starting point of reading, the area of positive cardioelectric potentials was located on the chest surface of the investigated animals cranially and that of negative potentials, caudally (figure). In ten pigs, positive cardiopotentials were recorded mainly on the ventral side of the body; in four pig, on the dorsal side. Within the subsequent 10 ms after the body surface cardioelectric field formation, in the period of atrial depolarization, the displacement of the zones of positive and negative cardioelectric potentials was observed. The change in their mutual location stopped at the initial stages of the P IIS formation.During the P IIS -wave ( 51 ± 6 ms), the zone of positive cardiopotentials occupied the caudal part and that of negative potentials, the cranial part of the body. This location did not change before the end of the initial atrial activity.During the ascending phase of the P IIS -wave (from 10 to 30 ms), the positive extremum shifted on the ven-PHYSIOLOGY *This article was translated by the authors. + -+ --+ + -P Equipotential instantaneous maps of the pig body surface during initial atrial activity. The regions of positive potentials are shaded; + and -indicate the location of the positive and negative extrema, respectively; the ECG recorded from the II sagittal lead is shown with a time marker (the vertical line).