Abstract: A wearable medical monitoring (WMM) system may be worn for a long time. Some embodiments of WMM systems are wearable cardioverter defibrillator (WCD) systems. In such systems, ECG electrodes sense an ECG signal of the patient, and store it over the long-term. The stored ECG signal can be analyzed for helping long-term heart rate monitoring of the patient. The heart rate monitoring can be assisted a) by special filtering techniques that remove short-term variations inherent in patients' short-term heart rate determinations, and b) by indication techniques that indicate when conditions hampered sensing of the ECG signal too much for a reliable heart rate determination.

Abstract: One or more electronic device may use motion and/or activity sensors to estimate a user's 6 minute walking distance. In particular, because users typically walk at less than their maximum output and in imperfect conditions, control circuitry within the device(s) may rely on walks of shorter distances to estimate the 6 minute walking distance. For example, the control circuitry may gather activity information for the user, such as heart rate, calories burned, and step count, and analyze a distance component and a speed component for periods in which the user has walked. Individual 6 minute walk distance estimates may be generated based on each of the activity information, distance component, and speed component. The distance and speed estimates may be corrected for walking behaviors that deviate from an ideal testing environment, and may then be fused with the activity estimate to generate a final 6 minute walk distance estimate.

Abstract: A wearable arrhythmia monitoring and treatment device for improving confidence in determined arrhythmias prior to treatment includes a plurality of sensing electrodes, one or more therapy electrodes, and an electrode signal acquisition circuit having a plurality of inputs. The electrode signal acquisition circuit is configured to sense a respective signal provided by each of a plurality of different pairings of the plurality of sensing electrodes. The wearable arrhythmia monitoring and treatment device includes a monitoring and detection circuit including at least one processor configured to analyze the respective signals provided by each of the plurality of different pairings of the plurality of sensing electrodes, change a confidence level in a determined arrhythmia condition based on the respective signals provided by the plurality of different pairings of the plurality of sensing electrodes, and initiate a therapy to the patient via the one or more therapy electrodes based on the confidence level.

Abstract: Improved devices, circuits and methods of operation in implantable stimulus systems. An implantable defibrillator may comprise an H-bridge output circuit having low and high sides, with a current controlling circuit coupled to the high side of the H-bridge output circuit and a current monitoring circuit coupled to the low side of the H-bridge output circuit. Alternate current paths to the output of the H-bridge, or to the H-Bridge itself, are used for delivering different therapies to the patient.

Abstract: A sleep system may include a control system for a bed device that includes platform upon which an individual may be supported. The sleep system may include multiple input sources that trigger combinational output action patterns with respect to the control system and bed device. The multiple input sources may include sensors positioned to collect input data with respect to the subject, bed device, and/or surrounding environment such as motion sensors, presence sensors, proximity sensors, sound sensors, temperature sensors, biological sensors, and/or light sensors.

Abstract: The invention provides a sensor for measuring both impedance and ECG waveforms that is configured to be worn around a patient's neck. The sensor features 1) an ECG system that includes an analog ECG circuit, in electrical contact with at least two ECG electrodes, that generates an analog ECG waveform; and 2) an impedance system that includes an analog impedance circuit, in electrical contact with at least two (and typically four) impedance electrodes, that generates an analog impedance waveform. Also included in the neck-worn system are a digital processing system featuring a microprocessor, and an analog-to-digital converter. During a measurement, the digital processing system receives and processes the analog ECG and impedance waveforms to measure physiological information from the patient. Finally, a cable that drapes around the patient's neck connects the ECG system, impedance system, and digital processing system.

Abstract: A heart rate detection module including a PPG measuring device, a motion sensor and a processing unit is provided. The PPG measuring device is configured to detect a skin surface in a detection period to output a PPG signal. The motion sensor is configured to output an acceleration signal corresponding to the detection period. The processing unit is configured to respectively convert the PPG signal and the acceleration signal to first frequency domain information and second frequency domain information, determine a denoising parameter according to a maximum spectrum peak value of the second frequency domain information to denoise the first frequency domain information, and calculate a heart rate according to a maximum spectrum peak value of the denoised first frequency domain information.

Abstract: Technologies and implementations for a wearable medical device (WMD). The technologies and implementations facilitate incorporating a blood oxygen saturation level device with the WMD. Additionally, the technologies and implementations include wearable cardioverter device (WCD) incorporating a blood oxygen saturation level device.

Abstract: The present invention relates to a system of multiple implantable medical devices for an impedance measurement comprising a first implantable medical device, at least a second implantable medical device distinct from the first implantable medical device and; an analysis module comprising at least one amplifier and one envelope detector, one of the first implantable medical device or the second implantable medical device being a subcutaneous implantable cardioverter defibrillator or a subcutaneous loop recorder, and the other of the first implantable medical device or the second implantable medical device being an implantable endocardial device.

Abstract: The inventive apparatus comprises a mat member. The mat includes a scale physically secured to the mat member. The scale has an electrical output strives an electronic circuit. A display displays a weight measured by the scale. A switch is distributed over an area roughly commensurate with the area needed to trot in place. The switch is secured to the mat and underlies a top surface of the mat. The switch is coupled to the electronic circuit. The electronic circuit is programmed to count the number of times that the switch is closed, whereby trotting in place results in closing the switch in response to trotting paces. The above transducers are used to monitor and crosscheck activity and dietary information input into the system by the user and make recommendations.

Abstract: System and methods for providing a patient with arrhythmia treatment are described. For example, a system includes an arrhythmia monitoring and treatment assembly configured to be worn on the torso of the patient. The assembly has a housing discreetly extending from a skin surface of the patient. The assembly is configured to provide therapy on detecting one or more arrhythmia conditions of the patient. A first at least one user response button is disposed on the assembly at a first location on the torso concealed under clothing, and a second at least one user response button is configured to be worn on a second location of the patient's body, a location other than the torso that is accessible to the patient. The system suspends an impending therapy upon receiving a user input from either one of the first or second at least one user response buttons.

Abstract: A composite electrode intracardiac defibrillation catheter includes a first electrode group including at least two first electrodes for detecting an electrophysiological electrical signal of a site or a cell group in a heart chamber, and a second electrode group including at least one second electrode located between an adjacent pair of the at least two first electrodes for causing an electric current by a high-voltage defibrillation electric shock for defibrillation to flow in a contact site in the heart chamber or a contact site in a vein, and a conductive length of a surface of the at least one second electrode in a longitudinal direction of the composite electrode intracardiac defibrillation catheter is longer than a conductive length of each of the at least two first electrodes.

Abstract: An ambulatory medical device configured to analyze heart rates in different operating modes includes a plurality of ECG sensing electrodes, a plurality of therapy electrodes and at least one processor configured to in a default operating mode, perform a default heart rate calculation for determining a heart rate of the patient for use in detecting a cardiac arrhythmia condition of the patient. The at least one processor is configured to change a device operating mode from a default mode based on detecting patient activity to an activity operating mode, and in the activity operating mode, perform a different heart rate calculation from the default heart rate calculation for determining the heart rate for use in detecting the cardiac arrhythmia condition of the patient during the activity operating mode. The at least one processor is configured to deliver the treatment in response to detecting the cardiac arrhythmia condition.

Abstract: 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.

Abstract: In one embodiment, a wearable cardioverter defibrillator (WCD) is described. The WCD includes a support structure worn by a patient. A processor is coupled to the support structure. The WCD also includes a discharge circuit coupled to an energy storage module, the discharge circuit configured to discharge the stored electrical charge through a body of the patient. The wearable cardioverter defibrillator also includes a user interface housing at least one sensor and responsive to changes in device orientation. The processor is configured to detect a motion at the user interface and determine when the motion is patient-activated. When the motion is patient-activated, the processor determines a direction of rotation. The processor determines an orientation of a display at the user interface based on the direction of rotation and orients the display at the user interface to appear upright to the patient.

Abstract: In embodiments, a wearable cardioverter defibrillator (WCD) system includes a support structure configured to be worn by an ambulatory patient, an energy storage module configured to store an electrical charge, at least one defibrillation electrode held on the patient while the patient is wearing the support structure, and sensors. The sensors may include a rotational measurement module, a magnetic field sensing module, a pulse detector and an ambient air pressure sensor. The sensors may gather multiple data about the patient, which can be used for better understanding of the patient's activities and ultimately a better-informed defibrillation decision.

Abstract: Methods and system for guiding a rescuer in placement of a defibrillation electrode may include initializing one or more cameras disposed on the defibrillation electrode, and capturing image information via the one or more cameras. Each image in a series of images may be acquired by the cameras after a set time interval. The method may include determining a separation distance between the defibrillation electrode and the chest of the patient and comparing the separation distance to a threshold distance. The method may further include determining whether the separation distance is below the threshold distance and, once the separation distance is below the threshold distance, determining a current location of the defibrillation electrode based on the series of images, and providing positioning feedback via at least one output device, wherein the positioning feedback includes instructions to move the defibrillation electrode toward a preferred location on the patient.

Abstract: A system and method for analyzing and logging changes in brain state of a subject for administering therapy to the subject based on the at least one cardiac signal wherein the system and method comprises the steps of receiving at least one cardiac signal of the subject into a processor, analyzing the cardiac signal to detect at least one cardiac signal change indicative of a brain state change, and logging at least one characteristic of the detected signal change or the brain state change.

Abstract: An implanted electrical signal generator delivers a novel exogenous electrical signal to a vagus nerve of a patient. The vagus nerve conducts action potentials originating in the heart and lungs to various structures of the brain, thereby eliciting a vagal evoked potential in those structures. The exogenous electrical signal simulates and/or augments the endogenous afferent activity originating from the heart and/or lungs of the patient, thereby enhancing the vagal evoked potential in the various structures of the brain. The exogenous electrical signal includes a series of electrical pulses organized or patterned into a series of microbursts including 2 to 20 pulses each. No pulses are sent between the microbursts. Each of the microbursts may be synchronized with the QRS wave portion of an ECG. The enhanced vagal evoked potential in the various structures of the brain may be used to treat various medical conditions including epilepsy and depression.

Abstract: An external medical device includes a user interface; at least one therapy electrode configured to be disposed on a patient; and a processor operatively coupled to the at least one therapy electrode, the processor configured to cause a treatment manager to detect a cardiac condition of the patient; receive, via the user interface, discomfort information descriptive of the discomfort experienced by the patient; responsive to determining from the discomfort information that the patient is unconscious, execute at least one pacing routine, the at least one pacing routine being associated with the cardiac condition; and responsive to determining from the discomfort information that the patient is conscious, adjust at least one characteristic of the at least one pacing routine.

Abstract: A wearable electronic device which can detect a wearing state, comprising: at least one first electrode, provided in a first region of the wearable electronic device; at least one second electrode, provided in a second region of the wearable electronic device; a capacitance calculating circuit, configured to calculate first capacitances generated by the first electrode and configured to calculate second capacitances generated by the second electrode, wherein the capacitance calculating circuit further calculates a capacitance difference between the first capacitance and the second capacitance; and a processing circuit, configured to determine the wearing state according to the capacitance difference. Via such structure, a wearing state, a wearing location, a wearing angle of the electronic device can be automatically detected, thus the problem caused by an improper wearing manner can be improved.

Abstract: A wearable defibrillator includes garment configured to be worn by a patient, treatment electrodes configured to apply electric current to the patient, and an alarm module configured to provide audio, visual, and haptic notifications. The notifications are configured to indicate that an electric current will be administered imminently, and prompt the patient to provide a response input. The wearable defibrillator includes a motion sensor configured to detect motion and a lack of motion of the patient, and a controller in electrical communication with the alarm module and the motion sensor. The controller is configured to monitor for the response input, cause administration of the electric current to be delayed or cancelled if the response input is received and motion of the patient is detected, and cause administration of the electric current to be delivered if no response input from the patient is received and a lack of motion is detected.

Abstract: A therapeutic device comprises an ECG sensing electrode configured to be disposed on a torso of a subject, a therapy electrode to be disposed on the torso of the subject, the therapy electrode comprising a substrate and a conductive layer disposed on a lower surface of the substrate, and an acoustic sensor coupled to one of the ECG sensing electrode and the therapy electrode, the acoustic sensor being configured to acoustically couple to the torso of the subject and monitor heart sounds indicative of a state of health of a heart of the subject. The therapeutic device is configured to store data regarding the heart sounds monitored by the acoustic sensor and transmit the stored data to an external system for processing and analysis.

Abstract: Methods and systems that analyze electrocardiogram (ECG) data to identify whether it would be beneficial for a caregiver to administer an electric shock to the heart in an effort to get the heart back into a normal pattern and a consistent, strong beat. By conducting a running check for conditions that are pre-validated by a comprehensive patient database to have high predictive value (e.g., with a low false-positive rate), a shockable rhythm can be identified fast (e.g., less than 6 seconds, less than 3 seconds, possibly in less than a second) and without having to analyze ECG data for longer time segments than would otherwise be required using conventional methods.

Abstract: Wearable devices are provided herein including wearable defibrillators, wearable devices for diagnosing symptoms associated with sleep apnea, and wearable devices for diagnosing symptoms associated with heart failure. The wearable external defibrillators can include a plurality of ECG sensing electrodes and a first defibrillator electrode pad and a second defibrillator electrode pad. The ECG sensing electrodes and the defibrillator electrode pads are configured for long term wear. Methods are also provided for using the wearable external defibrillators to analyze cardiac signals of the wearer and to provide an electrical shock if a treatable arrhythmia is detected. Methods are also disclosed for refurbishing wearable defibrillators. Methods of using wearable devices for diagnosing symptoms associated with sleep apnea and for diagnosing symptoms associated with heart failure are also provided.

Abstract: A patient monitoring device includes an ECG sensor coupled to a patient, a sensor coupled to the patient and configured to bio-vibrational signals, and a radio frequency monitoring device configured to produce information responsive to electromagnetic energy reflected from the patient's thoracic cavity. A processor processes the ECG signals, the bio-vibrational signals, and the radio frequency information to generate a plurality of physiological parameters of the patient. The processor also performs at least one of a predictive analysis and a trend analysis of the plurality of physiological to determine a current clinical condition of the patient. The trend analysis includes determining a substantial relationship between changes in the plurality of physiological parameters.

Abstract: 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.

Abstract: End-tidal carbon dioxide (ETCO2) measurements may be used alone as a guide to determine when to defibrillate an individual. Alternatively, ETCO2 measurements may be used in combination with amplitude spectral area measurements as a guide to determine when to defibrillate an individual.

Abstract: A computation apparatus, a cardiac arrhythmia assessment method thereof and a non-transitory computer-readable recording medium are provided. In the method, electrocardiography (ECG) signal is obtained. Whether the ECG signal is conformed to a first abnormal rhythm symptom is determined. Then, whether the ECG signal is conformed to a second abnormal rhythm symptom different from the first abnormal rhythm symptom is determined based on the determined result of the first abnormal rhythm symptom. Accordingly, multiple abnormal rhythm assessments are integrated, the subsequent assessment is speeded-up and optimized according to the determined result of a previous assessment, so as to enable to implement on a handheld apparatus.

Abstract: There is provided a context detection apparatus for use with a medical monitoring device arranged to measure a physiological characteristic of a subject. The context detection apparatus comprises at least one context sensor comprising a camera; and a processing unit. The processing unit is arranged to receive image data acquired by the camera from the at least one context sensor; analyze the received image data to generate a plurality of different types of context information; wherein each type of context information comprises information which relates to a factor capable of influencing measured values of the physiological characteristic and which is not measurable by the medical monitoring device; and output a signal to the medical monitoring device based on the generated context information.

Abstract: A portable telemetry device includes a physiological component, a fall detector component, a radio, and a communication component. The physiological component is configured to receive, from at least one sensor, physiological data representative of a physiological condition of a patient. The fall detector component is configured to detect a fall of the portable telemetry device. The radio is configured to wirelessly send radio signals. The communication component is configured to transmit the physiological data and an indication of the fall to a monitoring system using the radio.

Abstract: Techniques are described for real-time phase detection. For the phase detection, a signal is correlated with a frequency component of a frequency band whose phase is being detected, and the correlation includes predominantly decreasing weighting of past portions of the signals.

Abstract: An electronic device worn on a user includes one or more accelerometers. The one or more accelerometers generate acceleration information based on acceleration experienced by the electronic device. The electronic device further includes a processor and one or more associated memories, and the one or more associate memories include computer program code executable by the processor. The processor, configured by the computer program code, causes the electronic device to process the acceleration information to extract features from the acceleration information. The processor, configured by the computer program code, further causes the electronic device to process the features to determine the location of the electronic device on the user.

Abstract: A system and method for monitoring nerve activity in a subject. The system includes a plurality of electrodes placed in proximity to skin of the subject, an amplifier electrically connected to the electrodes and configured to generate a plurality of amplified signals corresponding to electrical signals received from the subject through the electrodes, and a signal processor. The signal processor applies a high-pass filter to the amplified signals to generate filtered signals from the amplified signals, identifies autonomic nerve activity in the plurality of filtered signals; and generates an output signal corresponding to the filtered signals. The high-pass filter attenuates a plurality of the amplified signals having frequencies that correspond to heart muscle activity during a heartbeat.

Abstract: This document presents a system for managing treatment for an emergency cardiac event. The system includes memory, one or more electronic ports for receiving ECG signals, and a treatment module executable on one or more processing devices. The module is configured to perform a number of transformation on portions of an ECG signal into frequency domain data, obtain one or more previous values derived from one or more time segments of the ECG, and determine, based on the frequency domain data a first value and a second value, determine a probability of therapeutic success. The module is further configured to cause one or more output devices to present an indication of the probability of therapeutic success.

Abstract: Cardiac electrodes and techniques for testing application of the electrodes to a victim are described herein.

Abstract: A system (10) for pedestrian use includes an accelerometer (110) having multiple electronic sensors; an electronic circuit (100) operable to generate a signal stream representing magnitude of overall acceleration sensed by the accelerometer (110), and to electronically correlate a sliding window (520) of the signal stream with itself to produce peaks at least some of which represent walking steps, and further operable to electronically execute a periodicity check (540) to compare different step periods for similarity, and if sufficiently similar then to update (560) a portion of the circuit substantially representing a walking-step count; and an electronic display (190) responsive to the electronic circuit (100) to display information at least in part based on the step count. Other systems, electronic circuits and processes are disclosed.

Abstract: An external defibrillator estimates the phase of ventricular defibrillation (VF) by deriving, from an ECG exhibiting VF, at least one quality marker representing the morphology of the ECG and, therefore, the duration of the VF. The duration of the VF is calculated as a function of the value (s) of the quality marker (s). The quality marker (s) may comprise any one or more of the median slope of the ECG, the average slope of the ECG, the ratio of the power in relatively high and low frequency bands of the ECG, and a measure of the density and amplitude of peaks in the ECG, over a predetermined period.

Abstract: A therapeutic device comprises a therapy electrode that includes a substrate, a conductive layer disposed on a lower surface of the substrate, an electrically conductive gel reservoir configured to release an electrically conductive gel onto a surface of the conductive layer, and an acoustic sensor coupled to the therapy electrode. The acoustic sensor is configured to acoustically couple to a body of a subject to which the therapy electrode is applied and to detect sounds indicative of a state of health of the subject. The therapeutic device is configured to transmit data regarding the sounds detected by the acoustic sensor to an external system for processing and analysis.

Abstract: Methods, apparatuses, and computer readable mediums for waistband monitoring analysis for a user are provided. In a particular embodiment, a waistband monitoring device is configured to generate a motion pattern based on motion data from a motion sensor coupled to the waistband monitoring device; receive physiological data generated by a physiological sensor coupled to the waistband monitoring device, wherein the physiological data indicates at least one vital sign of the user; identify an activity of the user that corresponds to the motion data and the physiological data; and generate an analysis of the user's performance of the identified activity based on the motion data and the physiological data.

Abstract: Embodiments of the present invention include a portable medical device with an integrated web server. The portable medical device is configured to establish a communication session with a user device. The integrated web server is configured to load software onto the user computing device for exchanging data with the portable medical device.

Abstract: Systems and methods for determining a cardiac condition of the human based on acceleration measurements received from one or more accelerometers of a garment worn by a human, electrocardiogram measurements received from electrodes of a garment worn by the human, and a machine learning model previously determined based on training data. An alert message that indicates the determined cardiac condition may be transmitted or displayed to the human wearing the garment or another person who will assist the human. For example, a posture pattern may be determined based on the acceleration measurements. The cardiac condition may be determined based in part on the posture pattern.

Abstract: Method, apparatus and computer-accessible medium for monitoring sleep quality of a user are described. For example, using such exemplary Method, apparatus and computer-accessible medium, it is possible to collect body movement signals of the user during sleep, and calculate body movement energy of a preset time-slot, based on the body movement signals collected during the preset time-slot. It is also possible to calculate an estimation threshold of a preset estimation time-span including the preset time-slot, based on body movement energy of preset time-slots which are included in the preset estimated time-span. Further, a determination can be made as to a sleep state of the user based on a comparison between the body movement energy of the preset time-slot and the estimation threshold of the preset estimation time-span. Such exemplary Method, apparatus and computer-accessible medium facilitate a strong adaptive ability and highly reliable sleep monitoring.

Abstract: A method of performing transthoracic defibrillation is described. The method includes generating at least two different defibrillation waveforms using at least two different defibrillation circuits contained in separate housings, delivering each of the at least two different defibrillation waveforms across a respective electrical path of a plurality of electrical paths established across the thoracic cavity and through the heart of a patient by at least three electrodes attached to the thorax of the patient, and synchronizing delivery of the at least two different defibrillation waveforms with communications between the separate housings.

Abstract: Appropriate cardiac therapy is determined by data sensed and analyzed by the disclosed defibrillators and other medical devices that one or both of treat and monitor a patient. The disclosed devices sense various patient physiological parameters including patient pulse and breathing data to determine whether the patient has a pulse and to determine if the patient is breathing. Depending on the analysis of the generated patient physiological data, the disclosed devices determine the appropriate therapy for the patient, which can include providing breathing assistance to the patient and providing electrotherapy and other therapies to the patient. Some of the disclosed medical devices can be wearable by the patient. The disclosed devices can include therapy modules like electrotherapy for delivering therapies to the patient while other devices monitor but do not deliver the therapies to the patient.

Abstract: Disclosed herein are methods and apparatus including medical devices having features for monitoring sounds and motions indicative of a state of health or administration of CPR to a subject. In one embodiment, a therapeutic device such as a therapy electrode comprises a layer configured to deliver a therapy to a subject and an acoustic sensor on the therapeutic device and coupled to the layer.

Abstract: Embodiments relate to an implantable cardiac system, including a housing, electronic circuitry for controlling one or more of power management, processing unit, information memory and management circuit, sensing and simulation output. The system also includes diagnosis and treatment software for diagnosing health issues, diagnosing mechanical issues, determining therapy output and manage patient health indicators over time, a power supply system including at least one rechargeable battery, a recharging system, an alarm (or alert) system to inform patient of energy level and integrity of system, communication circuitry, one or more electrodes for delivering therapeutic signal to a heart and one or more electrodes for from delivering electrocardiogram signal from the heart to the electronic circuitry. The present embodiments further include a body orientation unit to determine body position and use same to control therapy.

Abstract: A system and method are described for delivering electrotherapy to a patient that includes delivering electrotherapy to defibrillate the patient and providing at least one non-interruptible time period for administration of CPR prior to entering a monitor mode during which a patient cardiac signal is monitored for indication of a shockable rhythm.

Abstract: In embodiments, a WCD system includes one or more transducers that may sense patient parameters from different parts of the patient's body, and thus render physiological inputs from those parameters. Individual analysis scores may be determined from the physiological inputs, and an aggregate analysis score may be determined from the individual analysis scores. A shock/no shock determination may be made depending on whether or not the aggregate analysis score meets an aggregate shock criterion. Accordingly, multiple inputs are considered in making the shock/no shock determination.

Abstract: An implantable medical device (IMD) is implanted in a patient. The IMD uses a plurality of electrode vectors to generate intrathoracic impedance measurements. The intrathoracic impedance measurements can be indicative of amounts of intrathoracic fluid in the patient. An accumulation of intrathoracic fluid may indicate that the patient is at an increased risk of experiencing a heart failure event in the near future. The IMD performs a vector selection operation on a recurring basis. When the IMD performs the vector selection operation, the IMD uses impedance measurements to select one of the electrode vectors. The IMD can perform a risk assessment operation on another recurring basis. During performance of the risk assessment operation, the IMD uses impedance measurements of the selected electrode vector and/or other patient characteristics stored within the IMD to determine whether the patient is at an increased risk of experiencing a heart failure event.