successive cycles the condition of stability in amplitude means for example that the pea i peak amplitude does not vary by more than x compared to the average of the previous y cycles the condition of stability of coupling intervals means for example that the coupling interval does not vary by more or less z milliseconds for instance plus or minus 30 milliseconds from one cycle to the next in the presence of a stable pea rhythm revealing regular contractions the device determines step 14 whether the rate of these contractions frequency of pea peaks or f pea is lower than a limiting rate lower than the detection zone of tachycardiae f tachycardiae if not then the heart rhythm is probably a confirmed tachycardia for which a therapy shall be considered with no need to perform the fracture analysis any further otherwise in the presence of a rhythm of contractions that is sufficiently low the device examines step 16 whether it is in presence of a series of ventricular events with a short and variable coupling interval the criterion of u201c short coupling u201d means that the coupling intervals between successive ventricular events are lower than a given threshold and the criterion of u201c variable coupling u201d means that the differences between the coupling intervals are higher than a given threshold over a predetermined number of successive cycles if the analysis of the ventricular depolarizations.