Abstract: A defibrillator is designed for implantation in a patient and for programming certain of its parameters after implantation, including energy content of a shock waveform and timing of delivery of the shock waveform. A shock waveform generator of the device is responsive to a trigger signal for timed production of a shock waveform having a programmable shape and energy content designed for terminating atrial or ventricular fibrillation (AF or VF) of the patient. A detection circuit processes a sensed cardiac signal of the patient to determine the relative timing of various portions of the cardiac signal, including the P-wave and the T-wave.

Abstract: An implantable cardiac stimulating device which incorporates the functionality of both a pacemaker and an implantable cardioverter-defibrillator (ICD). The implantable cardiac stimulating device is adapted to periodically obtain an impedance measurement by applying a pacing pulse to the pacing tip and measuring the resulting current on a lead connected to one of the high voltage shocking coils implanted within the heart. The measured impedance between the pacing lead and the shocking lead is compared to previously obtained impedance measurements to determine if an increase in the impedance has occurred. The system is further adapted to compare the impedance measurement to the impedance measured between the pacing lead and the casing of the implantable cardiac stimulating device to determine whether any increase in the measured impedance is due to a problem with the pacing lead or a problem with the high voltage coil or high voltage lead.

Abstract: An intraoperative defibrillation test system for establishing defibrillation thresholds for an implantable cardioverter defibrillator (ICD) uses the actual ICD housing electrode, rather than a test housing electrode, as part of the test system. The intraoperative defibrillation test system includes the ICD, an external test station, and a test cable interconnecting the ICD with the test station. In one embodiment, the test cable is only connected to the ICD housing electrode and other test cables are used to connect to other implanted electrodes. In another embodiment, the test cable includes multiple conductors for connecting to all of the electrodes associated with the ICD, including the ICD housing electrode. In a further embodiment, the test cable includes a distal connector block that serves as a three-way T-between at least one port in a header of the ICD and an electrode lead.

Abstract: An apparatus for generating a waveform for use in externally defibrillating the heart of a patient includes a plurality of capacitors chargeable to respective charge potentials. A control apparatus is operatively coupled with the capacitors to sequentially interconnect the capacitors in a circuit with one another to generate the waveform. Structure including e.g. electrodes is operatively coupled with the capacitors and the control apparatus to apply the waveform to the chest of the patient. The waveform preferably includes an emulated first-phase substantially sinusoidally shaped pulse component having a first polarity. According to biphasic embodiments, the waveform also includes an emulated second-phase substantially sinusoidally shaped pulse component having a second polarity. The control apparatus preferably is constructed to truncate the emulated first-phase pulse component at a predetermined time, preferably based on a design rule used to calculate pulse duration.

Abstract: A defibrillator incorporates a method and device for determining the energy delivered to and electrical resistance of biological tissues. The defibrillator's method and device achieve these determinations by measuring the pre-discharge voltage on the defibrillator's capacitors which are to be discharged into the body; measuring the post-discharge voltage across the capacitors which are subsequently discharged into the biological tissues; and calculating both the energy delivered to the biological tissues and the electrical resistance of the biological tissues on the basis of the measured pre-discharge and post-discharge defibrillator capacitor voltages.

Abstract: An electrotherapy circuit administers to a patient a current waveform. The electrotherapy circuit includes a charge storage device, at least two discharge electrodes connected by electrical circuitry to opposite poles of the charge storage device, a sensor that senses a patient-dependent electrical parameter (such as a patient impedance sensor), and a control circuit. The control circuit is connected to the sensor and the charge storage device and controls discharge of the charge storage device through the electrodes.

Abstract: An electrotherapy circuit administers to a patient a current waveform. The electrotherapy circuit includes a charge storage device, at least two discharge electrodes connected by electrical circuitry to opposite poles of the charge storage device, a sensor that senses a patient-dependent electrical parameter (such as a patient impedance sensor), and a control circuit. The control circuit is connected to the sensor and the charge storage device and controls discharge of the charge storage device through the electrodes, based on the patient-dependent electrical parameter (such as the patient impedance) as sensed by the sensor. The discharge is controlled in a manner so as to reduce the dependence of peak discharge current on the electrical parameter (such as patient impedance) for a given amount of charge stored by the charge storage device.

Abstract: A wavefront direction mapping catheter system is disclosed which includes a wire catheter that, when placed on the inner surface of the heart, identifies the direction of the electric field wavefront, and provides output signals for indicating the manner in which a position controller of the system is to be operated for moving the distal tip portion of the catheter toward the source of the wavefront. The distal tip portion of the catheter includes a bipolar electrode array, preferably including first and second pairs of orthogonally arranged bipolar electrodes which provide signals to an analyzer of the system, whereby vector analysis of the wavefront is performed. The signal analysis permits the catheter to be moved toward and positioned at the source of the wavefront or within the wavefront circuit, with the present system thereafter being configured to effect radio frequency energization of the bipolar electrode array for tissue ablation.

Abstract: A lead integrity measurement system for a cardiac pacemaker/cardioverter/defibrillator (PCD) of the type comprising an implantable pulse generator (IPG) and a lead system including one or more pacing leads each having a proximal end coupled to a pacing terminal of the IPG and a distal end with at least one pace/sense electrode in contact with a patient's heart and a pair of defibrillation leads coupled to defibrillation terminals of the IPG and defibrillation electrodes implanted in relation to the patient's heart. In a lead impedance test mode, the terminal of a selected defibrillation lead under test is coupled to system ground, and an excitation voltage is applied in an excitation path from a force lead terminal selected from the pacing leads.

Abstract: This invention provides an external defibrillator and defibrillation method that automatically compensates for patient-to-patient impedance differences in the delivery of electrotherapeutic pulses for defibrillation and cardioversion. In a preferred embodiment, the defibrillator has an energy source that may be discharged through electrodes on the patient to provide a biphasic voltage or current pulse. In one aspect of the invention, the first and second phase duration and initial first phase amplitude are predetermined values. In a second aspect of the invention, the duration of the first phase of the pulse may be extended if the amplitude of the first phase of the pulse fails to fall to a threshold value by the end of the predetermined first phase duration, as might occur with a high impedance patient.

Abstract: An electrophysiology diagnostic device generating a high voltage (HV) pulse of a predetermined shape, which device is electrically connected to a patient's heart, i.e., a load resistance and which device includes a microprocessor and a load resistance measuring device, consists of a rapid response voltage threshold determination (RRVTD) circuit and a variable capacitance emulation (VCE) circuit. The RRVTD circuit receives an actual signal corresponding to the HV pulse waveform, compares the actual signal with a desired signal and produces an error signal when the actual signal deviates from the desired signal by a predetermined threshold value. The VCE circuit, which is capable of emulating a selected capacitance C, includes a fixed capacitor C.sub.0, and first and second branch circuits including respective resistors R.sub.1 and R.sub.2 and corresponding switching elements, connected in parallel with the load resistance R.sub.L.

Abstract: A method and apparatus for performing electrophysiologic testing on a patient's heart using an implantable pulse generator system. The system includes an implantable pulse generator such as an implantable cardioverter-defibrillator having high voltage capacitors for storing electrical energy to defibrillate the patient's heart, a means for inducing a cardiac arrhythmia, an electrode system for discharging the stored energy into the patient's heart, and an external programmer for communication with and command of the implantable pulse generator. The method comprises the steps of charging the capacitors to a selected energy level upon command from the external programmer, inducing fibrillation in the patient's heart following the charging step, and discharging the capacitors through the electrodes into the patient's heart to defibrillate the patient's heart. The method and system provides flexibility in electrophysiologic testing by allowing the physician to control the time of delivery of high voltage therapy.

Abstract: An implantable cardioverter defibrillator (ICD) system features rate-responsive pacing capabilities. An electrical pulse generating device having a housing containing pulse generating circuitry is provided. A conductive lead connectable to the housing that has a first electrode, a second electrode and a coil electrode is provided. Switching circuitry is provided contained in the housing that switches the coil electrode between the rate-responsive sensing electrode to a defibrillation electrode. Control circuity is provided within the housing for controlling the delivery of modulating signals to the coil electrode and for sensing changes in resistance between the coil electrode and the housing. The control circuitry also causes an alteration of the pacing signal applied to the pacing electrode depending upon the change in the resistance sensed.

Abstract: The present invention is a one piece, disposable pulse generator emulator for emulating a subcutaneous implantable cardioverter defibrillator (ICD) having an active housing electrode. The emulator of the present invention is for use with an external test system to screen a patient for candidacy for an ICD by determining the patient's minimum defibrillation threshold voltage. The one piece, disposable emulator has a housing that has substantially the same conductive geometry as the desired implantable pulse generator.

Abstract: An automated external defibrillator which automatically performs self-tests on a daily and weekly basis. Tested functions include the presence and interconnection of defibrillator electrodes, battery charge state and the operability of the high voltage circuit. Visual and audible indicators are actuated to alert an operator if faults are identified. A record of each self-test is stored in memory, and can be subsequently retrieved through a communications port.

Abstract: A method for detecting a heart disorder comprises examination of a phase-plane plot (PPP) of a patient electrocardiogram (EKG). The PPP's degree of deterministic chaos may be measured by a processor. Analysis of the PPP may indicate a propensity for fibrillation that is, indicate both the risk of fibrillation and its actual onset (cases where risk is 100 percent). A second method for detecting a heart disorder comprises examination of a frequency-domain transform (such as an FFT) of a patient EKG. An automatic defibrillating device may comprise means for delivering a variable shock, the size of which is determined at least in part by the FFT's peak energy. A method for detecting drug toxicity comprises examination of a parameter time constant for an action-potential duration (APD) restitution curve which is constructed for the patient.

Abstract: A method and apparatus for inducing fibrillation in a patient's heart by delivering an alternating current stimulus to the heart from a DC-to DC converter. The hardware of a conventional implantable cardioverter/defibrillator (ICD) is utilized with a modification to the control algorithms. Particularly, when it is desired to induce fibrillation in a patient's heart, typically during ICD implant defibrillation threshold (DFT) testing, a command is delivered from an external instrument to the ICD to deliver the fibrillation shock. The DC-to-DC converter which is normally used to charge the ICD high voltage capacitors is activated and immediately thereafter a first pair the high voltage output switches of the output stage are closed for about 4 milliseconds. This delivers an initial pulse of one polarity. Following an interval of about 4 milliseconds, a second pair of the high voltage output switches are closed for 4 milliseconds delivering an opposite polarity pulse.

Abstract: Methods, circuits and devices useful for maximizing the likelihood of successful defibrillation or cardioversion using an automatic implantable cardioverter/defibrillator ("AICD") system are provided which are capable of monitoring the impedance of AICDs for purposes of detecting lead malfunctions. After detection of a lead malfunction, the methods, circuits and devices are capable of connecting or disconnecting leads and electrodes to maximize the likelihood of effective cardioversion and defibrillation.

Abstract: A system and method for predicting the defibrillation threshold energy of a defibrillation lead arrangement by determining the upper limit of vulnerability of the heart by shocking the heart at varying times during the T-wave at decreasing test shock energy levels until fibrillation is induced in the heart. The lowest energy level which fails to induce fibrillation is determined to be the upper limit of vulnerability and the defibrillation threshold is predicted to be an energy level incrementally higher in the range of about 5 Joules.

Abstract: A periodic electrical lead integrity testing system is provided which periodically tests electrical leads used with an implantable cardiac stimulating device. The system is especially advantageous in multi-functional implantable cardiac stimulating devices. Lead integrity is evaluated by periodically comparing the impedance of the electrical leads to a reference impedance. A pass/fail algorithm is used to determine if electrical lead integrity has been compromised. The system improves the efficacy and safety of implantable cardiac stimulating devices by detecting electrical failures independent of the delivery of therapeutic shocks. The required circuitry adds only minimal complexity and cost to the implantable cardiac stimulating device.

Abstract: An implantable device, such as a defibrillator which may include cardioversion and pacemaker capabilities, which automatically measures the impedance of the heart prior to the delivery of a cardioverting shock. The defibrillator adjusts the voltage level on output capacitors to deliver a selected energy to the patient's heart. Insulated gate bipolar transistors, or similar devices having an inherent capacitance such that when they are turned on a small voltage gradient will exist across the transistor, are used as switches to control the application of electrical energy to the heart for therapy. When the switches are turned on, a current flows through a connected circuit path, for example through the heart and associated leads. Measurement of the current gives a measure of the impedance of the heart. An initial measurement is performed at the time of implantation of the implantable device, when the initial energy level (and output voltage) is selected.

Abstract: A method for rapidly and accurately determining defibrillation thresholds. The method comprises the steps of delivering an initial shock series to a patient, the shock series comprising at least two shocks of differing energy levels, determining an estimated shock level adjustment based on the initial shock series, and delivering at least one adjusted shock of a predetermined energy level based on the estimated shock level adjustment. The technique uses optimized search criteria as opposed to the conventional step-wise decrease and increase techniques. An apparatus for implementing the method is also disclosed.

Abstract: An implantable cardiac defibrillator system, comprising:a) a charge storage element,b) a switching element connected to the charge storage element,c) a processor capable of detecting a defibrillation event in a patient,d) patient connection electrodes connected to the switching element and to the processor,e) a cardiac impedance monitoring section connected to the patient connection electrodes, andf) a charge storage element discharge section communicatively connected to the switching element.

Abstract: An implantable atrial defibrillator cardioverts the atria of a patient's heart and determines the quantity of cardioverting electrical energy required for cardioverting the atria of the patient. The atrial defibrillator includes a detector for detecting atrial activity of the heart and an atrial fibrillation detector for determining when the atria of the heart are in fibrillation. A delivery stage is selectively operable in a test mode for applying fibrillation inducing electrical energy to the atria when the atria are not in fibrillation for inducing fibrillation. When fibrillation is induced, the delivery stage repeatedly applies test cardioversion electrical energy to the atria until the atria are cardioverted. Thereafter, a value indicative of the quantity of the test cardioversion energy last applied to the atria is stored for future reference when the atrial defibrillator is in a normal operating mode.

Abstract: A defibfillator has a self healing storage capacitor connected in parallel with a safety resistor, and a microcontroller. Upon receipt of a calibration request, the microcontroller charges the capacitor to a charging voltage greater than a starting voltage, then discharges the capacitor through the safety resistor. As the capacitor is discharging, the microcontroller continuously measures the voltage across the capacitor. When the microcontroller detects that the voltage across the capacitor is less than or equal to a starting voltage, a timer in the microcontroller is started. When the microcontroller detects that the voltage across the capacitor is less than or equal to an ending voltage, the timer in the microcontroller is stopped. The microcontroller then determines an elapsed time between the time the timer was started and stopped. The microcontroller then calculates a capacitance value of the capacitor based on the starting voltage, the ending voltage, and the elapsed time.

Abstract: A method and apparatus for delivering an adaptive n-phasic waveform to the heart in either a fixed-tilt delivery mode or a fixed-duration delivery mode. A first phase of a first polarity is delivered to the heart. The first phase is set to terminate upon decaying to a preset level. If the first phase does not decay to the preset level within a predetermined maximum period of time, the first phase is terminated and the subsequent phases are delivered in a fixed-duration delivery mode. Because the first phase did not decay fast enough, it is determined that the patient has a relatively high system impedance. Therefore, subsequent phases will be delivered to the patient in a fixed-duration mode to insure the defibrillation is reversed. Otherwise, if the first phase decays to the preset level in less than the maximum predetermined period of time, it is determined that the patient has a relatively low system impedance and subsequent phases should be delivered in a fixed-tilt mode.

Abstract: A method and apparatus for determining the actual capacitance of a capacitor in a cardiac stimulating device in order to determine the potential necessary to store a desired amount of energy on the capacitor, are provided. The discharge curve of the capacitor is measured during re-forming to determine the time constant of the capacitor and the dumping resistor, and hence the actual capacitance.

Abstract: An apparatus for charging living tissue with electrical pulses has a charging capacitor that, for discharging, is connected via a controllable switch to electrodes in the region of the tissue. In order to achieve a curve of the current through the electrodes that deviates from an exponentially decaying curve, the switch is switched on and off with a varying switching frequency while the tissue is being charged with pulses and the current supplied to the tissue is smoothed by circuit components.

Abstract: An implantable defibrillator provided with a plurality of defibrillation electrodes, which may be reconfigured to define a plurality of defibrillation pathways. The device is capable of measuring the impedance along a selected defibrillation pathway, during delivery of an impedance pulse, and monitoring the success or failure of the pulse to accomplish defibrillation or cardioversion. In response to a detected failure to accomplish cardioversion in conjunction with a measured change of impedance of greater than a predetermined amount, a new defibrillation pathway is selected, which may employ some or all of the electrodes employed to define the original impedance pathway. The device also includes apparatus for varying the relative amplitude of defibrillation pulses applied to individual electrodes used in sequential or simultaneous, multiple electrode pulse regimens, in order to equalize current distribution, in response to measured pathway impedances.

Abstract: A unitary, flexible, substantially noncollapsible catheter tube of biocompatible material is comprised of hard and soft regions. The hard regions can be ring shaped or helical. The hard regions provide sufficient rigidity to the tube to prevent collapse under normal usage as the interior and exterior pressures vary. The soft regions provide sufficient flexibility to allow contoured placement of the tube. The hard regions can be created by exposing a polymer in the tube to radiation. The hard regions can also be created by periodically adding a harder material to the tube.