Pacing leads cardiac depolarization

Fig. 3.11 Intrinsic cardiac depolarization can be recorded at the pacing lead electrode and measured by the pacemaker. This signal is called an electrogram. In this example, the electrogram is measured from the ventricular lead and is caused by ventricular depolarization. The signal has an amplitude of 8mV. This signal would not be seen by the pacemaker if the sensitivity is set to 10 mV. However, by lowering the sensitivity value to 5 mV (making the pacemaker more sensitive), the intrinsic depolarization would be seen and pacemaker timing cycles would be reset when appropriate.

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