An implantable device, such as an implantable cardiac rhythm management device (e.g., a pacemaker, a defibrillator, or a cardioverter), may be used to monitor cardiac function and provide therapy for a patient who suffers from cardiac arrhythmia. For example, in an attempt to maintain regular cardiac rhythm, the implantable device may track the type and timing of native cardiac signals. In this way, the implantable device may determine whether cardiac events (e.g., contractions) are occurring and whether they are occurring at the proper times.
The implantable device may track cardiac signals through the use of one or more leads implanted in or near the heart of the patient. For example, the implantable device may process signals received via implanted leads and then attempt to characterize the received signals as a particular cardiac event. Such cardiac events may include, for example, P-waves, R-waves, T-waves, or arrhythmia events.
By analyzing the type and timing of these cardiac events, the implantable device may determine whether therapy should be provided and, if so, the type of therapy to be provided (e.g., stimulation pulses). For example, if the implantable device detects desired cardiac events at the appropriate relative times, the device may simply continue monitoring for cardiac events.
In contrast, if arrhythmias are detected (e.g., cardiac events are not occurring at appropriate times or undesired cardiac events are detected), the implantable device may stimulate the heart in an attempt to restore normal cardiac rhythm. For example, in some cases, if a particular cardiac event has not been detected for a defined period of time, the implantable device may deliver an appropriate stimulation (e.g., pacing) pulse to the one or more chambers of the heart to make up for the missing cardiac event. Similarly, in cases where too many cardiac events of a given type are received over a defined time period (e.g., a tachycardia condition is detected), the implantable device may deliver electrical pulses via one or more implanted leads in an attempt to restore normal cardiac rhythm.
An implantable device also may be used to adapt therapy in other ways. For example, in some cases an implantable device may send data representative of the detected cardiac events to an external device (e.g., a home monitor). In this way, a treating physician may adjust the patient's therapy (e.g., prescribe a different drug, different amounts of a drug, or different stimulation parameters) based on the detected cardiac events.
In practice, not all arrhythmias are prognostic of worsening cardiac function. Thus, the detection of arrhythmias may not necessarily indicate that a change in therapy is warranted. Accordingly, a need exists for effective techniques for identifying arrhythmias that are indicative of a change in a patient's condition.