Apparatus and method for discriminating between heart rhythms with similar atrial and ventricular rates

An implantable medical device for monitoring and classifying cardiac rhythms of a patient's heart, comprising:

• means for sensing atrial and ventricular events of the heart;
• means for measuring intervals "AV" between atrial and ventricular contractions of the heart;
• means for measuring and storing "AVnsr", the AV internal of the patient's heart rhythm during resting normal sinus rhythm thereof;
• means for classifying said rhythms based on the timing of said sensed events;
• said classifying means including means for discriminating between tachycardias of physiological origin and tachycardias of pathological origin having overlapping ventricular rates, each of said tachycardia's having similar atrial and ventricular rates and each of said tachycardias having ventricular-ventricular intervals which are less than a predetermined minimum normal sinus interval, said discriminating means including means for forming an interval timing window having a first predetermined threshold shorter than said AVnse interval and a second predetermined threshold longer than said AVnsr interval;
• said classifying means including mean for classifying as pathological origin those of said tachycardias in which the Av intervals fall outside of said interval timing window;
• and
• said device further including means for utilizing the results of said classifying means.