Development of an optimal rechargeable cardiac pacemaker

While many rechargeable pacers, including a commercial unit have been developed using nickel-cadmium cells, they are in general limited by low cell capacity, short life without recharging, the need for frequent recharging, indirect monitoring of battery voltage by stimulation rate changes and gradually falling cell capacity with each cycle at body temperature. We have developed a low-drain rechargeable pacemaker, hermetically sealed in a seamless container, that will stimulate continuously for 4 yr without recharging. Our battery is a silver modified 1000 mA hr rechargeable version of the mercury-zinc cell proven by years of use in over 95% of pacers used clinically to date. It has functioned for over 6 yr in real time tests and in 120 accelerated tests has always simulated over 50 yr of pacing. Our pacer is small and thin, with less than one-half the displacement of current nonrechargeable units. Electromagnetic recharging energy is painlessly transmitted through the intact skin by a tuned coil, using a unique system unaffected by variations in implant depth. A telemetry oscillator permits noninvasive monitoring and telephone transmission of cell voltage, stimulation rate, implant depth, and optimal recharging coil location. Six animal and 3 clinical implants continue perfect function after up to 2.5 and 1 yr, respectively. A 6 yr life is proven and a greater than 20 yr life is anticipated.