Beep detection technique for immediate documentation of R wave sensing by an implanted defibrillator

A technique is described for follow-up clinic evaluation and documentation of R wave detection by an implanted defibrillator that emits audible tones upon magnet application whenever an R wave or other signal is sensed. A circuit comprising an electret microphone, an instrumentation amplifier, a high-pass filter, and an envelope detector is used to generate a signal that may be plotted together with a surface-lead electrocardiogram on a two-channel strip-chart recorder. The resulting plot documents the sensing function of the implanted device and serves as an indication of optimal magnet position. Alternatively, the beep detector output could be used to trigger the inscription of fiduciary markers on a single-channel strip-chart recorder equipped with an auxiliary input for this purpose.