Abstract: A circuit for indicating at a remote location the control states of a fully implantable heart pacer includes a parallel to serial converter which receives the control states from a register which controls the parameters of the associated pacer. When the pacer is switched to an asynchronous or to a magnetic mode, the data is shifted through the parallel to serial converter. A delay is added between pulses when a particular logic state appears, and no delay is added if the complement of that logic state appears. The parameters can therefore be determined externally by observing the successive periods between stimulation pulses in the asynchronous or magnetic mode of the pacer.

Abstract: A circuit for measuring the refractory period of a heart pacer includes first, second and third monostable multivibrators. The first monostable multivibrator is reset by the reception of a pacer stimulation pulse to produce a state change for a time period longer than the stimulation pulse interval of the pacer. The second monostable multivibrator is triggered by the trailing edge of the stimulation pulse, and has a variable time constant to produce a state change for a controlled period of time. The third monostable multivibrator applies a pulse to the pacer at the conclusion of the state change of the second monostable multivibrator. A counter is provided which counts the stimulation pulses produced by the pacer, and is connected to a resistive time constant circuit, to add additional time controlling resistors into the time constant circuit of the second monostable multivibrator.