A method of determining the susceptibility to ventricular arrhythmias in a subject, comprises the steps of: (a) collecting (e.g., by by surface EKG or intracardiac EKG) at least one QT and DI interval data set from the subject during a stage of gradually increasing heart rate or a stage of gradually decreasing heart rate; (b) determining (e.g., by applying low- and high pass filtering) low-frequency QT-DI interval trends and high-frequency QT-DI fluctuation signals in said at least one QT and DI interval data set; (c) finding a plurality of correlated and anti-correlated portions between said high-frequency QT-DI fluctuation signals; (d) determining corresponding regression lines for said correlated and anti-corelated portions; (e) finding a plurality of (or in some embodiments all) steady state QT-DI points designated by intersections between said low frequency QT-DI trends and said corresponding regression lines; (f) fitting action potential durations computed from a rate dependent reaction-diffusion model to corresponding ones of said steady state QT-DI points to give (i) a model excitation threshold and (ii) a minimal level of refractoriness at a plurality of (or in some embodiments all of) said steady state QT-DI points; (g) at the steady state QT-DI point corresponding to the highest heart rate in said QT and DI interval data set, determining the difference between said minimal level of refractoriness and a model critical excitation threshold for a stable solitary pulse corresponding to the rate dependent reaction diffusion model of step (f) to give a reserve of refractoriness (RoR); (h) fitting action potential durations computed from a rate dependent reaction-diffusion model to said correlated and anti-correlated portions to give a rate of adaptation of each model excitation threshold to a corresponding steady state value at a plurality of (or in some embodiments all of) said steady state QT-DI points; (i) at the steady state QT-DI point corresponding to the highest heart rate in said QT and DI interval data set, determining the inverse of said rate of adaptation to give a reserve of memory (RoM); (j) combining said reserve of refractoriness (RoR) and said reserve of memory (RoM) to produce a metric of stability-of-propagation reserve (SoPR) in said subject, a higher value of SoPR indicating lower susceptibility to ventricular arrhythmias in said subject. Systems and apparatus for carrying out the method are also described.
METHOD AND SYSTEM FOR EVALUATING STABILITY OF CARDIAC PROPAGATION RESERVE