An implantable cardiac stimulation system provides autocapture assessment and
lead impedance surveillance. The system includes a pulse generator that provides
pacing stimulation pulses and a lead system including a plurality of electrodes
that provide a plurality of different electrode configurations. The system further
includes a switch that selectively couples the pulse generator to any one of the
plurality of pacing electrode configurations and an autocapture circuit that performs
autocapture tests with the pulse generator. The autocapture circuit includes a
capture detector that detects evoked responses with an evoked response electrode
configuration. When there is a failure to detect an evoked response, an impedance
measuring circuit measures the lead impedance of the evoked response electrode
configuration. If the measured lead impedance is outside of a given range, the
switch couples the pulse generator to an electrode configuration other than the
evoked response electrode configuration. Thereafter, the autocapture circuit performs
a further autocapture and impedance measuring test or sets the pacing output to
a level which assures capture.