A report on an implantable electronic cardiac pacemaker.

The cardiac pacemaker, although comparatively new, is no longer in an experimental stage. It is now in the armamentarium of medical men and surgeons concerned with treating complete heart-block with Stokes-Adams seizures. Four or five years ago, when the need for such a device became obvious, several centers started working on different types of pacemakers that were reported almost simultaneously. Senning and Elmqvistl were probably the first to develop a permanently implantable electronic pacemaker (1959). Made by the Elema Company in Sweden, it had a passive receiver and an external power source. Chardack and associates"." in Buffalo, Zoll and co-workers4 in Boston, our group at Maimonides,5.s and other^^-^ developed implantable devices based on essentially the same principle. Weirich and associateslO had previously shown that far less energy is required to stimulate the heart with electrodes implanted in the myocardium than with Zoll's external stimulation method. Our pacemaker, developed with the General Electric Company, has undergone a number of modifications. The first unit was round, about 2.5 cm. in diameter, and weighed 4 oz. Its components were potted in epoxy resin and the case was of Teflon. Placed in an abdominal pocket, its electrodes were passed through a tunnel to the myocardium of the left ventricle where they were securely embedded. This device was extensively tested in dogs with good results, and we eventually used a similar one in our first clinical case, but it gave us some difficulties. The latest model has essentially the same components: 5 batteries, 2 transistors, 3 resistors, and 1 capacitor (Fig. 1). It has been amply demonstrated that the fewer the components in a device, the higher is its potential for safety and reliability.