Abstract: An implantable medical interventional device delivers electrical therapies to the heart of the implant patient to treat pathological tachycardia. A first sensor of the device generates a signal indicative of the patient's ECG, and a second sensor in the form of an activity sensor such as an accelerometer generates a signal representative of the current status of physical exercise by the patient. An evaluation system of the device establishes heart rate criteria for recognizing pathological tachycardias, to be applied against the ECG signal to recognize pathological tachycardia and distinguish it from physiological tachycardia experienced by the patient. A control system of the device modifies the criteria according to the nature of the exercise status signal, to enhance recognition and distinction. In an embodiment, the criteria of heart rate at the boundary between physiological and pathological tachycardia for the particular implant patient is modified by shifting it to a different rate.

Abstract: An implantable medical device, and more particularly a fully implantable defibrillator which may also include bradycardia and cardioversion pacing, in which the components of the device are housed within an implantable casing having three orthogonal dimensions of height, width and thickness. The height and width are substantially greater than the thickness. The implantable device comprises three major sub-systems, specifically, the batteries, the power capacitors, and the electronics. Each of the three sub-systems lie in parallel height-width planes, each plane being adjacent another in the thickness dimension.

Abstract: An implantable cardiac defibrillator includes a housing having a thickness dimension that is smaller than either of the length and width dimensions of the housing. Within the housing is an energy storage capacitor having a thickness dimension that is smaller than either of the length and width dimensions of the capacitor. The capacitor includes a first plate layer, a second plate layer, and a dielectric layer separating the first plate layer and the second plate layer. The first plate, second plate and dielectric layers are arranged spirally about an axis parallel to the thickness axis of the capacitor, with the thickness axis of the capacitor being substantially parallel to the thickness axis of the housing. The capacitor is arranged as an annulus having an open center. A battery is disposed within the open center in the same plane as the capacitor. A circuit board and header are arranged in another plane stacked atop the battery and capacitor.

Abstract: A variable rate implantable pacemaker responsive to patient exercise senses and distinguishes between distinct and different types of physical activity by the patient, and is programmed to respond by generating different response functions to control the pacing rate according to the specific type of physical activity detected. The response functions are algorithms, taken from the behavior of a healthy person with normally functioning cardiovascular system, of heart rates versus an appropriate parameter of a signal produced by a sensor carried by the patient, for the different types of activity requiring different algorithms, in which the parameter value varies in a predetermined way with exercise.

Abstract: An implantable variable rate cardiac pacemaker adaptive to patient exercise has a sensor responsive to each of several preselected different static physical positions of the implant patient to produce electrical output signals uniquely representative of the different physical positions. The pulse generator of the pacemaker is responsive to each output signal of the sensor to generate pacing pulses at a rate different from the rates generated in response to each of the other output signals of the sensor, so that each preselected different physical position has its own representative pacing pulse rate for stimulation of the patient's heart. The generator includes a rate control section adapted to respond to a change by the implant patient from one preselected physical position to another by producing a predetermined pattern of transition from the rate representative of the old position to the rate representative of the new position.

Abstract: An implantable cardiac stimulator with an analog-to-digital converter which comprises timing means for defining measurement cycles. During successive cycles, the value of a cardiac waveform is sampled. The difference between sampled values in two different measurement cycles produces a value whose probability is predicted. A digital code is assigned to each expected difference value such that difference values with a high expected probability have a shorter code and values with a low probability have a longer code. Means are provided for assigning a digital code based on the determined difference, the digital code being of predetermined variable size, the size of the code being proportional to the predicted probability of occurrence of a particular difference. The variability in code length permits the resulting digital representation of the waveform to be compressed and the energy required for conversion to be reduced.

Abstract: An implantable medical interventional device responds to detection of cardiac activity of the patient indicative of ventricular tachycardia (VT) or fibrillation (VF) by successively applying to the patient's heart selected ones of different electrical waveforms for treatment to break the VT or VF, respectively, until the monitored cardiac activity indicates that the treatment has been successful. An accelerometer adapted to sense position and movement of the patient along three mutually orthogonal axes acts as an activity status sensor to detect physical activity and inactivity of the patient to complement the detection of the patient's cardiac activity for confirming that a detected VT is a pathologic tachycardia rather than a physiologic tachycardia, and in response to such confirmation the device selects an appropriate electrical waveform for the treatment.

Abstract: A pacemaker with a variable, asynchronous minimum heart rate and a second variable, synchronous heart rate. The second, variable heart rate has an absolute minimum, lower than the asynchronous minimum heart rate, which is preselected by the attending physician. The minimum heart rates can vary, conditioned upon sensed physiologic need. The cardiac pacemaker attempts to reestablish synchrony in every cycle, even if the intrinsic or natural atrial heart rate is below the asynchronous minimum heart rate in that cycle and can maintain cardiac synchrony at lower rates, thereby increasing cardiac efficiency and minimizing strain on the heart.

Abstract: A subcutaneous data port which may be surgically implanted beneath the skin of a subject and electrically connected to implanted leads, sensors or an implanted medica device. The data port provides electrical connections through conductive rubber access ports. The access ports can be penetrated by a coated needle, establishing an electrical connection. An indifferent plate electrode provides a replicable ground or body reference electrode.

Abstract: A bipolar sensing lead for use with an implantable device, particularly a cardiac pacemaker, comprising a first sensing electrode located adjacent an outer surface of the lead and a second sensing electrode spaced away from that surface in at least two non-linear directions. In a preferred embodiment, the first sensing electrode is a ring electrode at the outer surface of the lead. The second sensing electrode comprises a conductive ring around the circumference of a collapsible, flexible disk.

Abstract: A lead system for a cardiac pacemaker comprising a lead having a proximal end and a distal end, the distal end having an electrode. A lumen passes through the lead from the proximal end to the distal end. A sensor-carrying flexible stylet is adapted to be inserted into the lumen of the lead. At the proximal end of the flexible stylet, there is an attachment means comprising a distal female connector and a proximal male connector adapted to connect to a pacemaker. The lead can also be provided with a distal aperture, which permits transport into the lead to the sensor of blood, gasses, heat, light, chemical or other phenomenon which are to be sensed.

Abstract: A pacemaker having an electrical stimulation source of known type is provided with a sense amplifier having a switched capacitor circuit which allows switching of the amplifier's bandpass frequency characteristic thereby selectively varying the cardiac signal frequencies subject to sensing. The heart's electrical activity is detected in a first predetermined low frequency range after to delivery of a stimuli to detect evoked electrical activity and a second predetermined high frequency range to detect intrinsic electrical activity. The magnitude of stimuli is varied response to the detected presence or absence of evoked electrical activity.

Abstract: An implantable endocardial lead with retractable sharpened helix. The piston has a central bore for receiving a specialized stylet. The stylet comprises a flexible wire having an enlarged distal end or tip. An elastomeric sliding sleeve fits over the wire. When the proximal end of the stylet is inserted into the bore in the piston, the wire can be withdrawn slightly, pulling the enlarged tip into the tube, and wedging the tube against the walls of the bore. By manipulating the stylet, the helix can be exposed outside of the lead, or retractable into the lead, as desired.

Abstract: A body function assistance device, capable of analyzing changing but cyclic physiologic needs of a patient and generating a response based on the analysis. A microprocessor in the body function assistance device controls the response of the device to various external events and internal timer events. The microprocessor recognizes variations in patterns of recurrent events and adjusts the output of the body function assistasnce device in response to the detected variations. In a particular embodiment, an implantable cardiac pacer is responsive to a circadian wake-sleep cycle.

Abstract: An implantable endocardial lead with retractable sharpened helix. The piston has a central bore for receiving a specialized stylet. The stylet comprises a flexible wire having an enlarged distal end or tip. An elastomeric sliding sleeve fits over the wire. When the proximal end of the stylet is inserted into the bore in the piston, the wire can be withdrawn slightly, pulling the enlarged tip into the tube, and wedging the tube against the walls of the bore. By manipulating the stylet, the helix can be exposed outside of the lead, or retractable into the lead, as desired.

Abstract: A state machine for automatic gain control of sensing functions in an implantale cardiac stimulator. The state controls sensing levels based on present sensed conditions and on the prior state of the heart. Different rates of adjustment are selected under varying conditions so that the gain level for sense amplifiers can be adjusted without significant overshoot. The state machine comprises a set of four conditions or states together with interconnections or logical paths from one state to another. The rate of adjustment of sense amplifier gain is based on the path traversed in the state machine so that different effective time constants for the control function may be used for different conditions.

Abstract: An implantable endocardial lead with retractable fixation means. The fixation means comprises a sharpened helix which can be repeatedly both retracted within an electrode at a distal end of the lead and displaced outside the electrode by action of a flexible, tubular lanyard. The landyard passes through a lumen from a proximal end of the lead to the distal end of the lead, where the lanyard is attached to a sliding member supporting the helix. At the proximal end of the lead, a jig moves th4 lanyard with respect to a longitudinal axis of the lead. When the helix is in an exposed postion, torque can be transmitted from the proximal end of the lanyard to the distal end thereof, through the piston and then to the helix to screw the helix into the endocardial tissue. To stiffen the lead during implantation, a stylet can be inserted into a lumen in the lanyard.

Abstract: A rate responsive cardiac pacemaker for implantation in a patient utilizes a pair of sensors. One is an activity sensor responsive to movements of the patient for generating an electrical signal representative thereof. A preselected component of the electrical signal generated by the activity sensor detected in a frequency range below 4 Hz distinguishes true physical exercise by the patient from other movements of the patient. The second sensor is responsive to a preselected metabolic function of the patient's body, such as central venous blood temperature, to develop an output signal representative of the present state of physical exercise of the patient. In response to (i) variation of the detected component in the range below 4 Hz and (ii) the output signal of the second sensor indicative of confirmation or lack of confirmation of physical exercise, the pacemaker generates pulses at a rate that varies according to a combination of those two.

Abstract: An implantable activity-based cardiac pacemaker has a variable rate stimulus generator housed together with an accelermeter and associated circuitry within a case. The accelerometer is isolated from the case to detect forces of acceleration on the case while avoiding response to pressure on the case, and to generate an electrical signal representative of the magnitude of the accelerational forces. The accelerometer is integrated into hybrid electronic circuitry, such as a semiconductor chip, together with an electrical circuit which processes the signal generated by the accelerometer to vary the rate of the stimulus generator according to the magnitude of the signal.

Abstract: An implantable variable rate pacemaker adaptive to patient exercise includes a motion sensor for detecting physical activity of the patient and producing an electrical signal having an amplitude vlaue representative of the intensity of the physical activity. The electrical signal is selectively limited to appreciable amplitude values for detected physical activity which is related to true physical exercise by the patient, in contrast to activity related to internal and external disturbances on the patient. The pacemaker compares the amplitude values of the selectively limited electrical signal to successively higher programmed threshold values representative of successively greater workloads of physical exercise to adjust the pacing rate to a higher rate as each of the threshold values is exceeded.