A method of assessing a patients susceptibility to ventricular arrhythmia obtaining data by applying electrodes to detect electrocardiographic signal. A plurality of synchronized subthreshold electrical stimuli are delivered into the patients body to present stimulated cardiac cycles to the electrodes and unstimulated reference cardiac cycles to the electrodes the signals are analyzed by creating a matrix of vectorized time-phase data representing a plurality cardiac cycles contained in the electrocardiographic signals that are recorded the method includes processing the matrix to generate spectral analytic representation of the matrix, analyzing at least the spectral analytic representation to determine at least one alternans index for the patient and displaying the at least one alternans index as an indicator of the patients susceptibility to arrhythmia.
