In part, the disclosure relates to computer-based methods, and systems suitable for evaluating a cardiac system using a diagnostic metric such as a pressure value-based ratio. Selection of a subset or portion of a cardiac cycle is avoided in one embodiment to increase reliability and usability of a diagnostic ratio and parameters described herein. In one embodiment, a minimum or a relative extrema of a series of diagnostic metrics plotted on a per cycle basis are used to inform diagnosis of a stenosis or other intravascular event or phenomena.
