Apparent Failure to Sense (Undersensing) Caused by Oversensing: Diagnostic Use of a Noninvasively Obtained Intracardiac Electrogram

Abstract

The ability to record noninvasively tbe intracardiac electrogram has potential advantages in the follow-up of paced patients. This case report illustrates one use of this feature in the evaluation of pauses in paced rhythm. Case ReportA 53-year-old woman had left bundle branch block, Type II second degree atrioventricular block, anda ventricular rate of 30 per min. A pacing system was implanted, which consisted of a bipolar porous-tipped tined electrode catheter connected to an interrogable multiprogrammable VVI pulse generator, which has the capability of radiofreciuency transmission of the electropram to the programmer.* The pulse generator parameters programmed at the end ofthe implant procedure were: rate -65 pulses per minute (923 ms automatic interval); pulse width -0.50 ms, sensitivity-1.5 mV; hysteresis interval-0.00 s; and refractory period -325 ms [in this model pulse generator, the refractory period after a paced complex is 16 ms longer than that after a sensed spontaneous complex).Immediately upon return to the tloronary Care Unit, pauses in paced rhythm were noted, along with apparent failure to sense(Flg.