Patent ID: 6879856

Claim:
Apparatus for treating tachyarrhythmias, comprising: means for delivering a first therapy to a patient's heart to treat tachycardia and a second therapy to said patient's heart to treat fibrillation; means for sensing an electrical signal from said patient's heart indicative of a depolarization of a chamber or chambers of said patient's heart; means for measuring a time interval between depolarizations; means for storing the measured depolarization intervals; means for detecting an occurrence of a tachyarrhythmia based upon the measured depolarization intervals; and means responsive to the detection of an occurrence of a tachyarrhythmia for discriminating between tachycardia and fibrillation and for selecting between said first and second therapies; said discrimination and therapy selection means including: (i) means for sorting a predetermined number of the measured depolarization intervals into a plurality of interval range bins; (ii) means for determining the number of measured depolarization intervals within each of the interval range bins; (iii) means for defining a discrimination criterion based on determining whether designated ones of the plurality of interval range bins have at least a predetermined threshold number of measured depolarization intervals within them, wherein the threshold number is set as a value which decreases as a function of the length of the intervals between depolarizations; and (iv) means for triggering delivery of the first therapy if the discrimination criterion is met and for triggering delivery of the second therapy if the discrimination criterion is not met.