An improved method and apparatus for assessing time-variant waveforms and identifying artifacts of interest therein. In one exemplary embodiment, an iterative interval search technique is applied to ECG waveform data in order to identify one or more artifacts (e.g., right atrial and right ventricular "spikes") within the waveform in conjunction with a fuzzy logic noise threshold analysis. This technique allows for robust artifact identification in waveforms where significant variations in noise and artifact periodicity may exist. The identified artifact(s) may then be used as an input to another process, such as being substituted as an ECG "Q" point for subsequent fiducial point detection within a cardiographic impedance waveform. Apparatus including computer programs for implementing the aforementioned techniques are also disclosed.