Miniature heart-monitoring devices, such as defibrillators and
cardioverters, are implanted in humans to detect and correct abnormal
heart rhythms Microprocessors and stored instructions, or algorithms
within these devices govern how they interpret and react to abnormal
heart rhythms. Algorithms that are too simple lead to unnecessary
shocking of the heart, while those that are too complex consume
considerable battery power. Accordingly, the inventor devised a
relatively simple yet accurate algorithm for determining appropriate
therapy options. One version of the algorithm computes three
statistics--a range statistic, a minimum interval statistic, and a
dispersion index--from a set of depolarization intervals. A scalar
interval dispersion assessment, based on the three statistics, is then
compared to a threshold to identify a rhythm as a flutter or
fibrillation.