Method and apparatus for adjusting cardiac event detection threshold based on dynamic noise estimation

An implantable medical device, comprising:

• a sensing circuit adapted to sense a cardiac signal, the sensing circuit including a signal filter adapted to produce a filtered cardiac signal having a signal frequency band by filtering the sensed cardiac signal;
• a noise estimation circuit coupled to the sensing circuit, the noise estimation circuit adapted to dynamically generate a noise floor using a noise signal having a noise frequency band, the noise floor being an estimate of noise level in the signal frequency band, the noise estimation circuit including a noise filter adapted to produce the noise signal by filtering the sensed cardiac signal or the filtered cardiac signal, the noise frequency band allowing for estimation of noise energy across the signal frequency band;
• and
• an event detection circuit coupled to the sensing circuit and the noise estimation circuit, the event detection circuit adapted to dynamically adjust a detection threshold using at least the filtered cardiac signal and the noise floor and to detect cardiac electrical events using the filtered cardiac signal and the detection threshold, the noise floor used as a minimum value of the detection threshold.

An implantable medical device, comprising:

• a sensing circuit adapted to sense a cardiac signal, the sensing circuit including a signal filter adapted to produce a filtered cardiac signal having a signal frequency band by filtering the sensed cardiac signal;
• a noise estimation circuit coupled to the sensing circuit, the noise estimation circuit adapted to dynamically generate a noise floor using a noise signal, the noise floor being an estimate of noise level in the signal frequency band, the noise estimation circuit including a noise filter adapted to produce the noise signal by filtering the filtered cardiac signal, the noise signal having a noise frequency band that is substantially different from the signal frequency band;
• an event detection circuit coupled to the sensing circuit and the noise estimation circuit, the event detection circuit adapted to dynamically adjust a detection threshold using at least the filtered cardiac signal and the noise floor and to detect cardiac electrical events using the filtered cardiac signal and the detection threshold, the noise floor used as a minimum value of the detection threshold;
• a peak measurement circuit adapted to measure peak amplitudes of the filtered cardiac signal;
• and
• a low signal-to-noise ratio (SNR) detection circuit adapted to calculate a running average of the peak amplitudes, calculate a dynamic SNR being a ratio of the running average of the peak amplitudes to the noise floor, and indicate a low SNR when the dynamic SNR is lower than a threshold SNR.

An implantable medical device, comprising:

• a sensing circuit adapted to sense a cardiac signal;
• the sensing circuit including a signal filter adapted to produce a filtered cardiac signal having a signal frequency band by filtering the sensed cardiac signal;
• a noise estimation circuit coupled to the sensing circuit, the noise estimation circuit adapted to dynamically generate a noise floor using a noise signal, the noise floor being an estimate of noise level in the signal frequency band, the noise estimation circuit including a noise filter adapted to produce the noise signal by filtering the filtered cardiac signal, the noise signal having a noise frequency band that is substantially different from the signal frequency band;
• an event detection circuit coupled to the sensing circuit and the noise estimation circuit, the event detection circuit adapted to dynamically adjust a detection threshold using at least the filtered cardiac signal and the noise floor and to detect cardiac electrical events using the filtered cardiac signal and the detection threshold, the noise floor used as a minimum value of the detection threshold;
• a therapy output circuit to deliver one or more cardiac therapies;
• a control circuit coupled to the sensing circuit, the event detection circuit, and the therapy output circuit, the control circuit adapted to control the delivery of the one or more cardiac therapies using at least the detected cardiac electrical events;
• and
• an implantable housing configured to contain the sensing circuit, the noise estimation circuit, the event detection circuit, the therapy output circuit, and the control circuit.