Implantable cardiac stimulation device, system and method which provides an electrogram signal facilitating measurement of slow-changing electrogram features

An implantable cardiac system including an implantable cardiac stimulation device, the system providing a heart activity signal of a heart facilitating measurement of slowly changing electrogram features, the system comprising:

• at least one implantable electrode arrangement that senses cardiac electrical activity and provides an intracardiac electrogram signal;
• a first high-pass filter with a cutoff frequency at an upper frequency breakpoint that filters the intracardiac electrogram signal, and
• an equalizer that filters the filtered intracardiac electrogram signal, the equalizer having a transfer function derived by multiplying a reciprocal of the transfer function of the first high pass filter by a transfer function of a second high pass filter with a cutoff frequency at a lower frequency breakpoint, wherein the transfer function of the equalizer is non-decreasing for frequencies up to the lower frequency breakpoint.