A medical apparatus, including a probe or catheter, adapted for insertion into a heart of a subject with cardiac fibrillation, preferably with atrial fibrillation, more preferably with persistent atrial fibrillation, the probe including an elongated body, and one or more mapping electrodes or optical fibers disposed on a distal portion of the body, a memory having programs stored therein, a display, and a processor linked to the display that is coupled to access the memory to execute the programs, characterized in that the processor is connectable to receive an input provided by the mapping electrodes or optical fibers, wherein the programs cause the processor to perform the steps of obtaining a single or multiple electrical unipolar signals or optical signals from a single target or multiple sequential targets in the heart via the mapping electrodes or optical fibers, generating an electroanatomical map based on the assigned electrical or optical data of a single or multiple cardiac spots, and wherein the programs are capable of performing the following steps: a. Detecting activations over i) the electrical unipolar signals or ii) the optical signals; b. Obtaining the instantaneous frequency modulation (iFM) signal from the activations of step a) for each i) unipolar electrical signal or ii) optical signal, by calculating the reciprocal of the intervals between consecutive activations, preferably in seconds; and obtaining the instantaneous amplitude modulation (iAM) signal from the sequence of amplitude excursions of i) the negative deflections that contain activations in each unipolar electrical signal or ii) the optical phases 0 that contain activations in each optical signal: wherein the lower an amplitude excursion, the higher its corresponding value in the iAM signal and vice versa; c. Detecting intervals that display the footprint of rotational activity characterized by A) simultaneous increase in iFM and iAM (reaching a certain iAM threshold), which is indicative of drifting rotors approaching a cardiac spot or B) simultaneously high iAM and iFM values, which is indicative of stationary rotors or rotors meandering around a cardiac spot; d. Calculating the mean, median or a specific percentile value (e.g. 90 th percentile) of each iFM signal obtained in step b), and obtaining a map by interpolating such values at each of the points used to generate the map, and using such a map to detect cardiac spots wherein such mean, median or specific percentile values are higher than those in their surroundings, such cardiac spots being considered to be the regions potentially driving cardiac fibrillation ('drivers' or 'high-hierarchy' regions); and e. Presenting the electroanatomical map on the display in any way in which the 'driver' or 'high-hierarchy' regions detected in step d) and the cardiac spots displaying the footprint of rotational activity detected in step c) can be identified in the heart of a subject. a. Detecting activations over i) the electrical unipolar signals or ii) the optical signals; b. Obtaining the instantaneous frequency modulation (iFM) signal from the activations of step a) for each i) unipolar electrical signal or ii) optical signal, by calculating the reciprocal of the intervals between consecutive activations, preferably in seconds; and obtaining the instantaneous amplitude modulation (iAM) signal from the sequence of amplitude excursions of i) the negative deflections that contain activations in each unipolar electrical signal or ii) the optical phases 0 that contain activations in each optical signal: wherein the lower an amplitude excursion, the higher its corresponding value in the iAM signal and vice versa; c. Detecting intervals that display the footprint of rotational activity characterized by A) simultaneous increase in iFM and iAM (reaching a certain iAM threshold), which is indicative of drifting rotors approaching a cardiac spot or B) simultaneously high iAM and iFM values, which is indicative of stationary rotors or rotors meandering around a cardiac spot; d. Calculating the mean, median or a specific percentile value (e.g. 90 th percentile) of each iFM signal obtained in step b), and obtaining a map by interpolating such values at each of the points used to generate the map, and using such a map to detect cardiac spots wherein such mean, median or specific percentile values are higher than those in their surroundings, such cardiac spots being considered to be the regions potentially driving cardiac fibrillation ('drivers' or 'high-hierarchy' regions); and e. Presenting the electroanatomical map on the display in any way in which the 'driver' or 'high-hierarchy' regions detected in step d) and the cardiac spots displaying the footprint of rotational activity detected in step c) can be identified in the heart of a subject.