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 filter, the mechanical chest compression device having a chest compression frequency f suitable for cardiopulmonary resuscitation of a person experiencing cardiac arrest 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 deliverable to the patient by the mechanical chest compression device, and wherein the at least one filter mechanism is configured to substantially reject content in the frequency f and to substantially reject content in at least one more frequency that is a higher harmonic to the frequency f but to substantially pass frequencies between the frequency f and the higher harmonic, characterized in that the filter is a high-Q, non-adaptive comb filter, where Q is at least 16. 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 filter, the mechanical chest compression device having a chest compression frequency f suitable for cardiopulmonary resuscitation of a person experiencing cardiac arrest 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 deliverable to the patient by the mechanical chest compression device, and wherein the at least one filter mechanism is configured to substantially reject content in the frequency f and to substantially reject content in at least one more frequency that is a higher harmonic to the frequency f but to substantially pass frequencies between the frequency f and the higher harmonic, characterized in that the filter is a high-Q, non-adaptive comb filter, where Q is at least 16. 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 filter, the mechanical chest compression device having a chest compression frequency f suitable for cardiopulmonary resuscitation of a person experiencing cardiac arrest 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 deliverable to the patient by the mechanical chest compression device, and wherein the at least one filter mechanism is configured to substantially reject content in the frequency f and to substantially reject content in at least one more frequency that is a higher harmonic to the frequency f but to substantially pass frequencies between the frequency f and the higher harmonic, characterized in that the filter is a high-Q, non-adaptive comb filter, where Q is at least 16.