Medical device for automatic diagnosis of undersensing by timing

A testing system, for use in an implantable medical device, said implantable medical device having sensing means for sensing a patient's atrial heartbeat signals, said testing system to determine whether said sensing means is missing atrial senses due to undersensing, said testing system comprising:

• atrial interval means for continually determining an interval time values between atrial senses;
• data means for obtaining a mean value for said interval time values, and for determining from said mean value a nsr variance value for a normal sinus atrial rate and a sss variance value for a sick sinus atrial rate;
• determining means for determining a statistically long atrial interval and for determining from said nsr variance value and said sss variance value and said mean value a measure of probability that said long interval was due to undersensing;
• and
• comparison means for comparing said measure with a predetermined undersense threshold to determine whether said long interval was due to undersensing.

A method carried out by a dual chamber pacemaker for determining when atrial undersensing is occurring, comprising:

• sensing atrial signals and determining from said sensed atrial signals atrial intervals between said sensed atrial signals;
• storing values of said atrial intervals;
• obtaining statistical data representative of said stored atrial intervals, said statistical data including variance values for a normal sinus rate and a sick sinus rate;
• detecting an occurrence of a statistically long atrial interval;
• determining, based on said long atrial interval, said stored atrial intervals and said statistical data, whether said long interval was due to atrial undersensing.

An implantable medical device, comprising:

• atrial sense means for sensing atrial signals from a patient;
• long interval means for determining when there is a long interval between two successive atrial signals;
• undersense means for determining when a said long interval is to be classified as an undersense, said undersense determining means comprising:
• first probability means for determining a first probability that said long interval was due to undersensing by said atrial sense means;
• second probability means for determining a second probability that said long interval was due to patient sick sinus syndrome;
• and
• classifying means for classifying said long interval as an undersense based on a function of said first and second probabilities.

A method for use in an implantable device for determining whether long atrial intervals included between atrial beats of a sensed atrial signal are a result of one of undersensing a absence of atrial beats, the method comprising the steps of:

• a.) calculating an average time interval between said atrial beats of said sensed atrial signal;
• b.) a long atrial interval between two successive ones of said atrial beats that is longer than said average time interval by a predetermined value;
• c.) calculating probability data descriptive of sick sinus syndrome rates and probability data indicative of undersensing rates based on said average time interval;
• and
• d.) determining, based on said probability a whether said long atrial interval is due to one of sick sinus syndrome, undersensed normal sinus rate, and a cause that can not be determined.

An implantable medical device, comprising:

• an atrial signal sensor to sense atrial signals;
• a processor coupled to said atrial sensor to a.) calculate a mean value for intervals between successive ones of said atrial signals, to b.) determine whether any said interval between successive ones of said atrial signals is indicative of a long atrial interval, and to c.) calculate a variance from said mean value for each said long atrial interval;
• and
• a storage device coupled to said processor to store probability distribution signals descriptive of the rate of said atrial signals, wherein said processor utilizes said probability distribution signals for determine whether said variance is indicative of one of an undersensed normal atrial rate and sick sinus syndrome.