Pulmonary vein as an ectopic focus in digitalis-induced arrhythmia

Abstract

The tunica media of the pulmonary vein (PV) in many mammalian species, including man, is made up of cardiac muscle^1–3. Brunton and Fayrer first reported that independent pulsation of the PV occurred in cats and rabbits even after activity of the heart had ceased⁴. Electrophysiological studies have also shown spontaneous electrical activity in isolated PVs of the guinea pig and a pacemaking region has been located at the distal end of the cardiac portion of the vein adjoining the smooth muscle. The intrinsic frequency of the PV was low and activity at the PV was normally coupled to the sinus rhythm⁵. Thus, the PV behaves as a subsidiary pacemaker. In the presence of digitalis-type agents, subsidiary pacemakers such as Purkinje fibres develop oscillatory afterpotentials (OAPs) which may be large enough to reach threshold^6,7, and it has been suggested that OAPs at Purkinje fibres leading to spontaneous action potentials may provide the underlying mechanism for ventricular arrhythmia during digitalis intoxication⁶. In contrast, atrial and ventricular muscles are not very sensitive to the arrhythmogenic action of digitalis⁸. I have therefore now investigated whether the PV can develop OAPs and act as an ectopic focus with digitalis intoxication. By recording with intracellular microelectrodes simultaneously at the PV and right atrium, I demonstrate that OAPs and repetitive activity develop at the PV in the presence of ouabain. Propagation of these triggered action potentials at the PV into the atrium results in atrial extrasystoles.