Data manipulation following delivery of a cardiac stimulus in an implantable cardiac stimulus device
Methods of cardiac rhythm analysis in an implantable cardiac stimulus device, and devices configured for such methods. In an illustrative embodiment, certain data relating to cardiac event rate or amplitude is modified following delivery of a cardiac stimulus. In another embodiment, cardiac rhythm analysis is performed using one of plural states, with the plural states using different criteria, such as a detection threshold, to detect cardiac events in a sensed signal. Following delivery of a cardiac stimulus, data is manipulated to force the analysis into one of the states, where stimulus is delivered, in the illustrative embodiment, only after a different state is invoked. Implantable devices incorporating operational circuitry for performing such methods are also included in other illustrative embodiments.
1. A method of cardiac signal analysis in an implantable cardiac stimulus device (ICSD) having electrodes adapted for implantation into a patient's body, the method comprising:
capturing cardiac signal data from a patient using the electrodes;
identifying cardiac events in the cardiac signal data;
estimating peak amplitudes in a plurality of the identified cardiac events;
estimating a rate of cardiac events from the identified cardiac events; and
determining whether cardiac stimulus is indicated using at least reference to the estimated rate and, if so delivering cardiac stimulus;
wherein the step of identifying cardiac events is performed by comparing the captured cardiac signal data to a detection threshold, wherein:
by default the detection threshold is mathematically related to the most recent estimated peak amplitude; and
after delivery of cardiac stimulus, the detection threshold is mathematically related to a predetermined value unrelated to the most recent estimated peak.
2. The method of claim 1 wherein the predetermined value is an estimate of cardiac signal amplitude during normal sinus rhythm of the patient.
3. The method of claim 1 wherein the steps of identifying, estimating and determining are performed in an iterative manner such that the determining and estimating steps are performed in any order following identification of a cardiac event.
4. The method of claim 1 further comprising:
following identification of a cardiac event, identifying and storing an interval associated with the cardiac event, the interval representing a period of time between a prior cardiac event and the most recent cardiac event; such that the step of estimating a cardiac event rate is performed using the stored intervals; and
following delivery of a cardiac stimulus, modifying data relating to stored intervals and/or the cardiac event rate such that, when the step of estimating a cardiac rate is next performed following identification of a cardiac event after delivery of a cardiac stimulus, a benign rate is estimated.
5. The method of claim 4 wherein the modified data is stored by the ICSD and is used in several calculations following delivery of the cardiac stimulus, until the modified data is replaced by data from additional identified cardiac events.
6. An implantable cardiac stimulus device (ICSD) comprising a plurality of electrodes for cardiac electrical sensing and/or therapy delivery; operational circuitry coupled to the plurality of electrodes including therapy delivery circuitry for delivering electrical cardiac therapy via the electrodes and analysis circuitry for analyzing cardiac signals in conjunction with processing circuitry, wherein the operational circuitry is configured to perform cardiac signal analysis and treatment as follows:
capturing cardiac signal data from a patient using the electrodes;
identifying cardiac events in the cardiac signal data;
estimating peak amplitudes in a plurality of the identified cardiac events;
estimating a rate of cardiac events from the identified cardiac events; and
determining whether cardiac stimulus is indicated using reference to the estimated rate and, if so delivering cardiac stimulus;
wherein the operational circuitry is configured such that the step of identifying cardiac events is performed by comparing the captured cardiac signal data to a detection threshold, wherein:
by default the detection threshold is mathematically related to the most recent estimated peak amplitude; and
after delivery of cardiac stimulus, the detection threshold is mathematically related to a predetermined value unrelated to the most recent estimated peak amplitude.
7. The ICSD of claim 6 wherein the predetermined value is an estimate of cardiac signal amplitude during normal sinus rhythm of the patient.
8. The ICSD of claim 6 wherein the operational circuitry is configured such that identifying cardiac events, estimating peak amplitudes and rate, and determining whether stimulus is indicated are performed in an iterative manner such that the determining and estimating steps are performed in any order following identification of a cardiac event.
9. The ICSD of claim 6 wherein the operational circuitry is further configured to:
following identification of a cardiac event, identifying and storing an interval associated with the cardiac event, the interval representing a period of time between a prior cardiac event and the most recent cardiac event; such that the step of estimating a cardiac event rate is performed using the stored intervals; and
following delivery of a cardiac stimulus, modifying data relating to stored intervals and/or the cardiac event rate such that, when the step of estimating a cardiac rate is next performed following identification of a cardiac event after delivery of a cardiac stimulus, a benign rate is estimated.
10. The ICSD of claim 9 wherein the operational circuitry is configured to store and use the modified data in several calculations following delivery of the cardiac stimulus, until the modified data is replaced by data from additional identified cardiac events.