Abstract

A tripolar catheter apparatus employing an automatic electronic switch is adapted for use with a conventional bipolar demand cardiac pacer for converting a bipolar pacing system into a tripolar pacing system in which stimulation can be applied between two intra-ventricular electrodes, such as ones located in the right ventricular apex, while sensing of ventricular depolarization may be obtained by an intra-ventricular apical electrode and an extra-ventricular electrode located outside the ventricle, such as in the right atrium or vena cava. The tripolar catheter apparatus comprises a pair of catheter terminals connected to the output terminals of the bipolar demand cardiac pacer and three output electrodes, namely a proximal electrode, a medial electrode and a distal electrode, which are provided to the heart. The distal electrode is the common electrode for both sensing and stimulation in the tripolar system while an automatic electronic switch selects either the proximal electrode or the medial electrode dependent on the provision of a cardiac stimulus from the pacer.