Robert R. Brownlee

Monitoring system for cardiac pacers

A complete system for telemetering and monitoring the functioning of an implanted pacemaker as well as controlling the testing of the functions from a remotely located central facility is disclosed specifically comprising the provision of capabilities for directly and simultaneously transmitting from the pacer, electrical signals indicative of multiple pacer functions, such as, pacer rate, cell voltage, refractory period, heart rate with pacer inhibited, R-wave level and sensing margin, sensing circuit and other component failure, cardiac electrode lead break, and hermetic integrity. The indicative signals are picked up at the patients location for local analysis and/or telephonically communicated to a remote central monitoring station. The central station may control testing of the pacemaker functions by transmitting command signals back telephonically for coupling through cooperating external and implanted inductances or magnetically controlled switches to the implanted pacer circuitry.

Toward Optimizing the Detection of Atrial Depolarization with Floating Bipolar Electrodes

Some concepts derived from modern lilerature on the physics of cardiac muscle conduction regarding optimization of the design of electrode systems for detection of atrial depolarization and a preliminary clinical corroboration of the concepts are presented. The concepts of most import are 1) that the mechanical dimensions of sensing electrodes in all planes have to be as small as possible relative to the dimensions of the extracellular waveform dimensions associated with depolarization action potentials, and 2) that the distance between bipolar electrodes should be tuned to be greater than the dimensions of the extracellular waveform to avoid subtractive interference patterns associated with saltatory propagation in aging cardiac muscle. Additionally, in the practical application of chronic atrial sensing from a single lead far use in an implanted VDD pacing system, it is also important to consider electrode size and its effect on impedance level.

Toward Optimizing a Preshaped Catheter and System Parameters to Achieve Single Lead DDD Pacing

P wave electrogram amplitudes and atrial stimulation thresholds were determined in eight Hanford miniature swine using a preshaped catheter with an “S” curve in the SVC, and a major lobe in the atrium to enhance electrode contact with the atrial wall. The catheter was designed for pacing and sensing in the DDD mode. P wave amplitudes were also ascertained with two commercially available VDD leads and compared to the data from the experimental catheters. The preshaped catheter used two 6‐mm2 platinum iridium atrial electrodes with a 7‐mm separation. Both atrial electrodes are on the same side of the catheter, facing outward on the major atrial lobe formed in the catheter. The P wave amplitudes were tested only in the differential bipolar configuration. For the eight preshaped catheters, the mean was 6.6 ± 3.8 mV while for the conventional leads it was 2.9 ± 1.6 mV. The mean atrial stimulation thresholds ranged from 1.1 t 0.2 V to 2.3 ± 1.2 V, with still lower thresholds of 0.9‐1.3 V when using the parallel unipolar atrial electrode configuration, in which both parts of the bipolar atrial electrode are configured as a unipolar electrode. The data suggest that bipolar stimulation may be effective if sequential reverse polarity pulses are used to achieve cathodal stimulation from each electrode of the bipolar pair, on a beat‐to‐beat basis. (PACE 1997; 20[Pt. I]:1354‐1358)

Utility of the Atrial Endocardial Electrogram Concurrent with Dual‐Chamber Pacing in the Determination of a Pacemaker‐Mediated Arrhythmia

A 73‐year‐old male required a permanent pacemaker for complete heart block. After placement of the dual‐chamber pacemaker, the patient developed random, repetitive ventricularly paced coupling at the upper rate limit. The diagnosis made from the surface electrocardiography was one of ventricular tracking of occult (T wave obscured) atrial ectopic activity. Examination of the telemetered atrial electrogram (EGM) revealed a diagnosis of intermittent far‐field atrial sensing of the terminal ventricular depolarization. The value of obtaining an atrial electrogram during dual‐chamber pacing is discussed.

A New Atrial Lead with Improved Stability and P‐Wave Detection

A new segmented polyether polyurethane atrial pacemaker lead has been developed and tested acutely and chronically in dogs. This lead was constructed so that its tip could q uick‐ly and accurately be positioned in close proximity to the S‐A node and provide long‐term stability without the use of active fixation devices such as tines or screws. The acute intrinsic P‐wave potentials seen at the S‐A node area (9.7 ± 4.7 mV) were superior to those defected in the appendage (4.7 ± 2.8 mV) and coronary sinus (6.8 ± 4.1 mV). There were no significant differences in pacing thresholds between sites. In long‐term studies, transvenous (juguiar) leads maintained their position for over three months without dislodgment in active unrestrained dogs with only a 25% decrease in intrinsic P‐wave potentials. The chronic pacing thresholds for this lead were similar, or superior, to those reported for other pacemaker lead placement sites. The polyurethane coating material produces no adverse tissue reaction or thrombosis.

Development of an optimal rechargeable cardiac pacemaker.

Abstract While many rechargeable pacers, including a commercial unit have been developed using nickel-cadmium cells, they are in general limited by low cell capacity, short life without recharging, the need for frequent recharging, indirect monitoring of battery voltage by stimulation rate changes and gradually falling cell capacity with each cycle at body temperature. We have developed a low-drain rechargeable pacemaker, hermetically sealed in a seamless container, that will stimulate continuously for 4 yr without recharging. Our battery is a silver modified 1000 mA hr rechargeable version of the mercury-zinc cell proven by years of use in over 95% of pacers used clinically to date. It has functioned for over 6 yr in real time tests and in 120 accelerated tests has always simulated over 50 yr of pacing. Our pacer is small and thin, with less than one-half the displacement of current nonrechargeable units. Electromagnetic recharging energy is painlessly transmitted through the intact skin by a tuned coil, using a unique system unaffected by variations in implant depth. A telemetry oscillator permits noninvasive monitoring and telephone transmission of cell voltage, stimulation rate, implant depth, and optimal recharging coil location. Six animal and 3 clinical implants continue perfect function after up to 2.5 and 1 yr, respectively. A 6 yr life is proven and a greater than 20 yr life is anticipated.

Rechargeable silver-modified mercuric oxide-zinc cell for cardiac pacemakers*

Tests were conducted on rechargeable mercury-zinc pacemaker batteries under simulated and actual biologic conditions, using a variety of discharge rates and charging schedules. In tests on 96 cells at a 6.4 milliampere (ma) discharge, recharging once every 15 months of simulated pacing at a 25 microampere (mua) drain, the earliest cell failure occurred after an equivalent of 50 years of pacing. The mean pacing equivalent for all 96 cells was more than 140 years. In 6.4 ma discharge tests on 24 cells, recharging once every 8 days of simulated pacing, only 1 cell in 24 failed after an equivalent of more than 500 years of pacing (actual time 2 years). In tests on 13 cells pacing at a 200 mua drain without recharging, the simulated mean duration of pacing before total discharge was 4.8 years. Seven other cells at a 200 mua drain with periodic recharging continue to function normally after more than 7 years of actual time, simulating 56 years of pacing at a 25 mua drain. Cardiac pacemakers using the rechargeable mercury-zinc cell have been implanted in animals for more than 2 1/2 years and in patients for more than 1 year with all units continuing to function satisfactorily. It has been demonstrated unequivocally that a rechargeable mercury-zinc pacemaker will function continuously for more than 4 years without recharging and that periodic recharging will extend pacing life far beyond that predicted for lithium and nuclear primary power sources.

A comparison of peak QRS potential detection using unipolar and bipolar cardiac pacemaker lead systems

Abstract The use of bipolar lead systems with demand cardiac pacemakers has been criticized because the small interelectrode distance was thought to decrease sensitivity to cardiac electrical potentials. This study was done to determine if the reduced interelectrode distance inherent in bipolar systems is a limiting factor with the new small surface area electrodes. Three bipolar electrodes of differing surface areas were placed in the right ventricule of 10 anesthetized dogs. Bipolar sensing was compared with unipolar sensing. The results demonstrated three factors which determine the amplitude of the potentials detected: (1) surface area of the electrode; (2) position of the indifferent ring electrode in the bipolar system; and (3) pacemaker sensing circuit impedance. Electrode surface area was the most important determinant and impedance was the least. No significant peak QRS potential differences were detected when bipolar and unipolar sensing with the newer small surface area electrodes were compared.

New Interference Sensing Demand Pacemaker Functions

Demand cardiac pacemaker functions are under study that provide new methods to distinguish between cardiac activity and pulsatile electromagnetic interference (PEMI). All known forms of currently marketed ventricular inhibited demand pacemaker (VVI) functions can be inhibited by high level pulsatile electromagnetic interference. The recent introduction of shielded circuitry to protect against disruptive (inhibiting) EMI has reduced pacemaker sensitivity to interference. However, EMI received via the cardiac lead/electrode can still mimic cardiac activity. This mimicing occurs as a consequence of detection by defribrillator protection structures or by amplifier saturation from RF artifacts insufficiently suppressed by input QRS bandpass filters. The new functions under development employ a separate EMI detection receiver for controlling the pacemaker mode to minimize inhibition by PEMI.

The Detection of Unipolar and Bipolar Cardiac Electrograms with a Movable Coaxial Electrode

Abstract To define the effects of endocardial positioning on the sensing electrodes ability to detect the cardiac electrogram, a specially designed coaxial lead system with a movable, large surface area (50 mm 2 ) proximal ring electrode and a small surface area distal tip electrode was placed transvenously in 17 mongrel dogs. When the sensing ring electrode was used in a unipolar mode, there were slight but insignificant decreases in R-wave amplitude while the ring remained in the ventricle. When the electrode was moved out through the valve into the atria there was a marked decrease in R-wave sensing, however, this was accompanied by a significant increase in P-wave amplitude. When the ring electrode was used in conjunction with the tip as a conventional bipolar system, the sensed R wave remained at uniformly high levels except when the two electrodes were very close together at the tip. P-wave amplitudes were not detected in the bipolar mode until the ring entered the atria.