Filter mechanism for removing ECG artifact from mechanical chest compressions

An external medical device, comprising:

• a housing;
• a memory within the housing;
• and
• a processor within the housing configured to:
• receive an input signal related to a patient receiving chest compressions from a mechanical chest compression device;
• cause the memory to store the input signal;
• as part of a post-event review, select at least one filter mechanism including a comb filter, the mechanical chest compression device having a chest compression frequency f;
• and
• as another part of the post-event review, apply the at least one filter mechanism to the stored input signal to at least substantially remove chest compression artifacts from the input signal, wherein the chest compression artifacts correspond to the chest compressions being delivered to the patient by the mechanical chest compression device, and wherein the at least one filter mechanism substantially rejects content in the frequency f and substantially rejects content in at least one more frequency that is a higher harmonic to the frequency f but substantially passes frequencies between the frequency f and the higher harmonic.