A decision support computer system for supporting diagnostic analysis of atrial flutter types, comprising: an interface component configured to receive an electrical reference signal generated by a reference sensor (CSCS), the reference signal providing a time reference for electrical activity of one or more atria of a patient wherein the time interval between two subsequent electrical activities is referred to as basic cycle length, and further configured to receive a plurality of electrical signals (P1 to Pi) generated by one or more further sensors (S1 to Sn) wherein the plurality of electrical signals (P1 to Pi) relate to a plurality of locations in the one or more atria, the plurality of locations comprising locations different from the location of the reference sensor (CSCS); a signal analyzer component configured to determine, for each signal of at least a subset of the received signals originating from locations within a selected area of the one or more atria, an active interval (ai1 to ai8) when electrical activity occurs, and a resting interval when no electrical activity occurs; and configured to compute, based on the determined intervals, a subset cycle length coverage as the ratio of duration of activity (DoA) and the basic cycle length wherein the duration of activity includes the active intervals for the entire subset of signals; and further configured to apply a Boolean OR operator to the determined activity and resting intervals of respective signals so that any activity interval of any signal contributes to the duration of activity, and no activity in all signals contributes to the duration of resting; and a visualizer component configured to indicate the selected area as an area including a potential focal source if the subset cycle length coverage is smaller than a predefined ratio, and else to indicate the selected area as an area including a potential re-entry. an interface component configured to receive an electrical reference signal generated by a reference sensor (CSCS), the reference signal providing a time reference for electrical activity of one or more atria of a patient wherein the time interval between two subsequent electrical activities is referred to as basic cycle length, and further configured to receive a plurality of electrical signals (P1 to Pi) generated by one or more further sensors (S1 to Sn) wherein the plurality of electrical signals (P1 to Pi) relate to a plurality of locations in the one or more atria, the plurality of locations comprising locations different from the location of the reference sensor (CSCS); a signal analyzer component configured to determine, for each signal of at least a subset of the received signals originating from locations within a selected area of the one or more atria, an active interval (ai1 to ai8) when electrical activity occurs, and a resting interval when no electrical activity occurs; and configured to compute, based on the determined intervals, a subset cycle length coverage as the ratio of duration of activity (DoA) and the basic cycle length wherein the duration of activity includes the active intervals for the entire subset of signals; and further configured to apply a Boolean OR operator to the determined activity and resting intervals of respective signals so that any activity interval of any signal contributes to the duration of activity, and no activity in all signals contributes to the duration of resting; and a visualizer component configured to indicate the selected area as an area including a potential focal source if the subset cycle length coverage is smaller than a predefined ratio, and else to indicate the selected area as an area including a potential re-entry.