An implantable medical device system is configured to sense cardiac events in response to a cardiac electrical signal crossing a cardiac event sensing threshold. A control circuit is configured to determine a drop time interval based on a heart rate and control a sensing circuit to hold the cardiac event sensing threshold at a threshold value during the drop time interval.

In some examples, a medical device system includes an electrode. The medical device system may include impedance measurement circuitry coupled to the electrode, the impedance measurement circuitry may be configured to generate an impedance signal indicating impedance proximate to the electrode. The medical device system may include processing circuitry that may be configured to identify a first component of the impedance signal. The first component of the impedance signal may be correlated to a cardiac event. The processing circuitry may be configured to determine that the cardiac event occurred based on the identification of the first component of the impedance signal.

An implantable medical device system is configured to sense cardiac events in response to a cardiac electrical signal crossing a cardiac event sensing threshold. A control circuit is configured to determine a drop time interval based on a heart rate and control a sensing circuit to hold the cardiac event sensing threshold at a threshold value during the drop time interval.

When a defibrillator selects a dosage of energy or current to be delivered to a patient, the defibrillator selects an excitation current frequency and applies the excitation current at the selected frequency to the patient. The frequency of the excitation current is selected as a function of the dosage to be delivered. The patient's response to the excitation current at the selected frequency will accurately reflect the impedance that the defibrillator will “see” when delivering the selected dosage of energy or current.

Embodiments of the disclosure include systems and methods for reducing false positives in detection of pauses. For example, embodiments include a sensing component configured to obtain values of a first physiological parameter and determine a cardiac pause based on the values of the first physiological parameter. Furthermore, embodiments include performing a validation check of the determined cardiac pause using at least one of: the values of the first physiological parameter or values of a second physiological parameter.

This disclosure relates generally to a computational model for personalizing defibrillation mechanism of wearable cardiac defibrillator (WCD). Cardiac defibrillators are lifesaving therapeutic device with potentially harming capacity if not tuned properly. Hence creation of a personalized energy distribution model based on subject's anatomy, rather than a ‘one size fits all’ approach is preferred. The disclosed model compares the efficiency of standard and nonstandard WCD electrode placement in the torso vest, demonstrating significant differences in defibrillation efficacy associated with different strategies. A new measure is presented for performing such a comparison which combines the DFT and extent of myocardial damage.

An example method is performed by a defibrillator that includes a therapy cable receptacle and an electrocardiogram cable receptacle. The method includes displaying a user interface screen that includes a primary channel for displaying a primary waveform and a secondary channel for displaying secondary data. The method also includes detecting a lack of a patient connection for therapy pads and detecting a patient connection for an ECG lead obtained using an ECG electrode cable. In addition, the method includes displaying a representation of an ECG signal obtained using the ECG electrode cable in the primary channel based on detecting the lack of the patient connection for the therapy pads and detecting the patient connection for the ECG lead.

In one embodiment, a WCD is described. The WCD includes a support structure configured to be worn by a patient and a processor coupled to the support structure. The WCD also includes an energy storage module configured to store an electrical charge and in communication with the processor. The WCD also includes a discharge circuit coupled to the energy storage module, the discharge circuit in communication with the processor and configured to discharge the stored electrical charge through a body of the patient. The processor is configured to detect an event at the WCD, classify the detected event, and determine an alarm onset time of the detected event based at least in part on the event classification. The processor is further configured to issue the alarm after the alarm onset time.

A medical device that includes a power source, a therapy delivery interface, therapy electrodes, electrocardiogram (ECG) sensing electrodes to sense ECG signal of a heart of a patient, a sensor interface to receive and digitize the ECG signal, and a processor. The processor is configured to analyze the ECG signal to determine a cardiac rhythm and a transform value representing a magnitude of a frequency component of the cardiac rhythm, analyze the cardiac rhythm and the transform value to detect a shockable cardiac arrhythmia by classifying the cardiac rhythm as a noise rhythm or a shockable cardiac arrhythmia rhythm based on the transform value, and causing the processor to detect the cardiac arrhythmia if classifying the cardiac rhythm as a shockable cardiac arrhythmia rhythm, initiate a treatment alarm sequence, adjust the shock delivery parameter for a defibrillation shock, and provide the defibrillation shock via the therapy electrodes.

Several defibrillators, defibrillator architectures, defibrillator components and methods of operating defibrillators are described. In one aspect, a defibrillator (as for example an automated external defibrillator) that can be powered by a mobile communication device such as a smart cellular phone or a tablet computer is described. Utilizing a phone (or other mobile communication device) as the power supply for an external defibrillator allows the external defibrillator to be smaller and, in some circumstance, removes the need for a battery that stores sufficient energy for shock delivery—which would need to be checked and/or replaced on a regular basis. Additionally, when desired, certain control functionality, computation, data processing, and user instructions can be handled/presented by the mobile communications device thereby further simplifying the defibrillator design and improving the user experience. This architecture takes advantage of the nearly ubiquitous availability of smart phones, tablet computers and other mobile communication devices.