An electrical connector includes a housing and a number of wafers. The first signal is sampled based on a sampling clock signal to generate a second signal. 00, wherein I\u03b3 is equal to I820-850I860-880 where I820-850 is a peak height resulting from a CH2 rocking band in \u03b3-phase PVDF and I860-880 is a peak height resulting from backbones in \u03b1- and \u03b3-phase PVDF. Electrocardiographic signals obtained from electrodes applied to the patient’s chest are analyzed so that the presence of a QRS signal characteristic of a rhythm which has the potential of supporting a beating heart, or the absence of a QRS signal which indicates ventricular fibrillation, may be detected in the presence of artifacts resulting from chest compressions. The seal assembly includes an annular seal member comprising polytetrafluoroethylene resin, backing rings on each side of the seal member, and an annular compression spring in the groove between one of the backing rings and one edge of the groove.