Apparatus for combining pacing and cardioverting functions in a single implanted device

The invention relates to an apparatus for combining pacing and cardioverting functions in a single implanted device, circuitry being provided not only to interface the defibrillator to the ECG amplifier and other elements of the device, but also to provide protection of the ECG amplifier from the defibrillator output pulses, from loading by the defibrillator itself, and from overloading by externally generated defibrillator pulses. A specific embodiment of the invention combines a defibrillator, a pacer and an ECG amplifier in a single implanted device utilizing two terminal-electrode lead combinations for connection to the patient, while further embodiments employ three and four terminal-electrode lead combinations. The invention employs a high-frequency transformer coupling technique for pacing, or, alternatively, high-frequency transformer coupling with modulation-demodulation. Moreover, in accordance with the invention, overloading of the ECG amplifier is prevented by provision of (in one embodiment) series-connected and oppositely oriented zener diodes, and (in a second embodiment) parallel-connected diodes in series with a blocking capacitor for blocking DC voltage.