The choice of the pacemaker-electrode combination.

The advantages of the endocardial electrode over the transthoracic electrode are illustrated by the fact that the Vth International Symposium on Cardiac Pacing in March 1976 in Tokyo a world wide survey of 15000 electrodes implanted in 1975 showed that 93.4% were of the tarnsvenous type. These advantages will be discussed. An important electrode choice that has to be made next is the selection between the monopolar and the bipolar electrode. Mechanical (electro), physiological and clinical aspects have pushed this choice towards the monopolar electrodes. The monopolar transvenous electrode is known in various types. The selection of the electrode can be determined by the incidence of electrode dislocation that has resulted in electrode tips with fixation principles like hooks, barbs and balloon or screw mechanism. For the longevity of a pacemaker system the efficiency of the electrode system is important, that means the energy needed for cardiac stimulation. This stimulation threshold is determined by the myocardial tissue, the stimulation impulse and the electrode, especially the electrode surface. Decrease of the surface area from 50 mm2 about 8-10 years ago to 5-10 mm2 raises the question if there exists an optimal surface area and optimal electrode shape. The electrode area can also influence the R-wave amplitude as detected by the pacemaker and therefore the electrode-pacemaker interface has to be discussed. The solution of some of the electrode problems, that has resulted in more sophisticated electrodes and improved electrode pacemaker systems, will be illustrated.