1. A non-transitory computer-readable memory medium that stores program instructions executable by a computer system to: receive a discrete electrocardiogram (ECG) signal, wherein the discrete ECG signal includes one or more waveform features indicative of cardiac condition; apply a sliding window multiscale frequency transform to the discrete electrocardiogram (ECG) signal, thereby generating a transform array parameterized by a specified plural set of window features; determine a plurality of peaks in the transform array, including determining coarse values for each of the specified plural set of window features for each peak; determine, for each peak, at least three windowed functions, wherein each of the windowed functions has window features with values approximately equal to the coarse values corresponding to the specified plural set of window features; and determine, for each peak, refined values for the plural set of window features based on the discrete ECG signal and the at least three windowed functions; wherein the refined values for the plural set of window features are indicative of a specified cardiac condition.