Noise detection system and method for use in an implantable medical device

In an implantable cardiac device, a system for detecting noise in an electrogram signal comprising:

• threshold circuit means for generating an event signal when the electrogram signal exceeds an event threshold;
• zero crossing detecting means for detecting zero crossings in the electrogram signal during a time period following an event signal;
• determining means for determining if the zero crossings detected by the zero crossing detecting means exceed a predetermined number;
• and wherein
• the electrogram signal is determined to be noise when the determining means determines that the detected zero crossings exceed the predetermined number during the time period.

In an implantable cardiac stimulation device, a method of detecting noise in an electrogram signal comprising:

• generating an event signal when the electrogram signal exceeds an event threshold;
• detecting zero crossings in the electrogram signal during a time period following an event signal;
• determining if the zero crossings in the electrogram signal exceed a predetermined number of zero crossings during the time period;
• and
• identifying the event signal as noise when the determining step determines that the electrogram signal exceeded the predetermined number.

In an implantable medical device, a system for detecting noise in a biological signal comprising:

• a timer that times a time period responsive to the biological signal, wherein the timer is configured to time a first refractory period portion and a second refractory period portion and wherein the time period is the combination of the first and second period portions;
• a zero crossing detector that generates a zero crossing signal when the signal transitions between preselected upper and lower threshold values;
• a counter that counts the number of zero crossing signals during the time period;
• a comparator that compares the counter to a predetermined count;
• and wherein
• the biological signal is determined to be noise if the counter exceeds the predetermined count during the time period.

In an implantable cardiac stimulation device, a method of detecting noise in an electrogram signal comprising:

• timing a time period that includes a first refractory period portion and a second refractory period portion wherein the time period is the combination of the first and second refractory period portions;
• detecting zero crossings in the electrogram signal occurring during the time period, said time period being initiated by the electrogram signal,
• determining if the zero crossings in the electrogram signal exceed a predetermined number of zero crossings during the time period;
• and
• identifying the occurrence of noise when it is determined that the number of zero crossings of the electrogram signal exceeds the predetermined number.

In an implantable medical device, a system for detecting noise in a biological signal comprising:

• a threshold circuit that generates an event signal when the signal exceeds an event threshold;
• a timer that times a time period responsive to an event signal;
• a zero crossing detector configured to generate a zero crossing signal when the biological signal either transitions from above an upper threshold to below a lower threshold or from below the lower threshold to above the upper threshold;
• a counter that counts the number of zero crossing signals during the time period;
• a comparator that compares the counter to a predetermined count;
• and wherein
• the biological signal is determined to be noise if the counter exceeds the predetermined count during the time period.

In an implantable cardiac stimulation device, a method of detecting noise in an electrogram signal comprising:

• generating an event signal when the electrogram signal exceeds an event threshold;
• detecting, during a time period following an event signal, when the electrogram signal transitions either from above an upper threshold to below a lower threshold or from below the lower threshold to above the upper threshold to detect a zero crossing thereby;
• determining if the zero crossings in the electrogram signal exceed a predetermined number of zero crossings during the time period;
• and
• identifying the occurrence of noise when it is determined that the number of zero crossings of the electrogram signal exceeds the predetermined number.