Clinical Experience with Permanent Atrioventricular Sequential Pacing

In a 23-month period, we implanted 26 permanent atrioventricular (AV) sequential pacing units in 11 women and 15 men ranging from 37 to 85 years old (mean, 68 years). Indications for pacing were complete heart block in 12 patients and sick sinus syndrome in 14 patients.Cardiac index, using standard thermodilution techniques, was determined in 9 patients during ventricular pacing and AV sequential pacing at constant heart rate. Atrioventricular sequential pacing was superior in all patients, with a mean increase in cardiac index of 22% (p < 0.01). Complications of AV sequential pacing included the need to revise two pulse generator pockets due to the large size of the pulse generator. One transvenous atrial lead displacement occurred in a patient who had previously undergone right atrial appendage ligation at open-heart operation. No failures of pacing or sensing occurred during 279 patient-paced months.The theoretical hemodynamic advantage of AV sequential pacing has been confirmed in this clinical trial. Experience with electrode placement and improvements in pulse generator design should aid in eliminating complications with this pacing modality.     

Clinical experience with the isotopic cardiac pacemaker.

Clinical experience with isotopic pacemakers in 59 patients is compared with that in 77 control patients having conventional chemical battery-powered pulse generators. The review covers a 51/2-year period. Statistical analysis of the two series is impossible because of the numerous variables such as age, type of disease, number of controls, types of test and control pulse generators, dates of insertion, and protocol regulations. However, there were pulse generator failures in the control group, but not in the test group. Though not proven in this study, the isotopic cardiac pacer is likely to last longer than conventional chemical battery-powered units, and could provide lifetime pacing for many patients. The risk of carcinogenesis is minimal and seems negligible in older patients. The isotopic cardiac pacer, in spite of restrictions of the Nuclear Regulatory Commission, should be considered for any patient with a life expectancy of 10 or more years. Paradoxically, it might be indicated in older rather than younger patients.     

Removal of Infected Epicardial Electrodes by Traction

Five patients who had infected cardiac pacemakers with epicardial electrodes have been managed by exteriorization of the pulse generator and placement of an endocardial unit. In each case the remaining electrode leads were detached from the myocardium and removed by simple traction, avoiding a surgical procedure.In 4 patients, sets of cables had been sutured to the myocardium through an anterior thoracotomy, in some instances using Teflon pledgets as buttresses. In one of these procedures a pericostal suture had been used to secure the leads from the thoracic cavity against the ribs. The remaining patient had received a subxiphoid pacemaker also implanted with sutures.This is a consecutive series, and we have had no failures so far. All pulse generator units were bipolar and located beneath either the pectoral or the rectus muscle. All of them were functioning properly when infection was diagnosed. This procedure constitutes an alternative method of management when more conservative techniques, such as closed irrigation and debridement, cannot be utilized.     

A new solid-state, long-life, lithium-powered pulse generator

A pulse generator powered by lithium iodide and using hybrid circuitry eliminates many of the causes of premature failure of pulse generators. The lithium iodide power source is completely dry, produces no gas, has no significant self-discharge, shows no catastrophic failure, is most efficient at body temperature, and loses power in a gradual fashion, thus giving months of foreknowledge of impending failure. The hybrid circuitry eliminates most soldered connections, which increases efficiency, reduces sources of failure, and allows a smaller pulse generator to be produced. The entire system can be hermetically sealed because no outlet for gas is required. The calculated in vitro life of this system is greater than 10 years, while a conservative estimate of in vivo life is 5 years.     

Pacing at a Very Short Pulse Width

From March, 1973, to June, 1975, 112 variable pulse width pulse generators (Medtronic 5931, 5961) were implanted in 109 patients. The devices were used routinely with both acute (59) and chronic (53) pacing electrodes. No special technique to obtain an unusually low pacing threshold was used or necessary.A chronic pulse width of 0.29 ± 0.07 msec was set, and no patient had failure to pace in the absence of severe electrode malfunction. Follow-up of between two and four and a half years is available on 93% (104) of the series, 8 patients having been lost to follow-up. A total of 38 pulse generators are out of service because of death unrelated to pacing (11), death related to pacing (3), electrode malfunction (16), pulse generator failure (5), or miscellaneous causes (3). Actuarial analysis for pulse generator failure shows a 92% survival at three years and 85% at four years with a total of 66 pulse generators remaining in service. Similar analysis shows a consistent incidence of 6% per year for both electrode malfunction from all causes and patient death from all causes.Clinical pacing at a pulse width shorter than that commonly used is safe and practical and results in a significant increase in the longevity of mercury cell-powered pacemakers. With the high cost and limited real-time longevity experience with pacemakers powered by lithium cells, a standard mercury-zinc pulse generator remains an acceptable alternative in selected patients.     

Preliminary clinical experience with a new radioisotope-powered cardiac pacemaker.

A small light-weight nuclear-powered pacer has been developed. The pulse generator weight 61 Gm. and occupies a volume of 33 sq. cm. It is a standard R-wave inhibited (VVI) demand pulse generator. The unit has met all United States and foreign atomic energy commission safety specifications including mechanical shock, industrial fire, accidental crush, cremation, impact, and corrosion. Its calculated life is in excess of 20 years. The unit has been shown to be insensitive to electromagnetic interference (EMI) over a wide range of commonly encountered sources of interference. An extensive dog testing program has been carried out and is continuing. The United States Atomic Energy Commission (AEC) has issued a license to conduct clinical trials. These began in October, 1974, and a total of 30 units of 30 units have been implanted so far. An equal number of chemical battery-powered pulse generators has been implanted in a control series of 30 patients. Preliminary results have been gratifying.     

Temporary pacing through permanent myocardial electrodes.

A technique is presented for using a permanent myocardial electrode for temporary pacing with a lead extension. The permanent myocardial electrode may be attached to a permanent pulse generator after a few days if long-term pacing is required.     

Management of the infected pacemaker: explantation, sterilization, and reimplantation

From January, 1970, through December, 1984, nineteen infected or eroded pacemaker units were reimplanted in 17 patients. Characteristics of the patients, types of infecting organisms, surgical management, and complications are described. Optimal treatment of the infected generator pocket requires explantation of the generator unit with utilization of the in situ leads for pacing by an external-demand pacemaker unit. The generator unit is sterilized, and new leads are placed with relocation of the pocket. The old leads are then removed. This technique has been used safely and with excellent results for the past fourteen years.     

Hydrogen washout technique in monitoring vascular status after replantation surgery

The hydrogen washout technique was applied to an experimental model of microvascular repair to evaluate its potential use in determining blood flow after microvascular surgery. Three blood flow measurements were obtained in each of 10 rat hindlimbs with the hydrogen washout technique: a control, a reading with arterial flow disrupted, and a final reading after standard microvascular repair of only the saphenous artery. After repair, flow rate was 0.115 ml/minute/ml compared to 0.008 ml/minute/ml for the disrupted reading (p < .01). The practical clinical applicability of the hydrogen washout technique for evaluating blood flow in the fingertip was tested on five human volunteers. Ischemia in the upper extremity was produced with a pneumatic tourniquet. The hydrogen washout technique and the Doppler pulse monitor were used simultaneously to evaluate circulation in the small finger. Hydrogen uptake occurred simultaneously with return of clinical signs of tissue perfusion during gradual tourniquet deflation. The Doppler pulse returned while clinical signs of ischemia remained. The use of hydrogen washout in monitoring three patients following microvascular surgery has shown it to be accurate in predicting survival. It has, thus far, proven itself to be easily repeatable and reliable both intraoperatively and postoperatively.     

Transtelephone pacemaker monitoring: five years later.

Six hundred nineteen patients have been followed by remote monitoring of pacemaker function using ECG and rate or rate alone; 278 of 280 have had battery exhaustion or electronic failure demonstrated. Ten percent of exhausted pacemakers failed prior to the average longevity of the particular model, and 32% (89 of 280) exceeded 36 months' longevity; of these, 13% (37 of 280) lasted more than 40 months and 4.6% (13 of 280) exceeded 50 months. The error rate is 0.7% (2 of 280). With pulse generator longevity increasing, monitoring is done less frequently during the first 2 years, then calls are made weekly after 24 months.     

In vivo study of a new radioisotope-powered cardiac pacer.

A new radioisotopic pulse generator has been developed. It is 6 cm. long, 4.7 cm. high, 1.92 cm. wide, and weighs 61 Gm. (2 oz.). It is the smallest pulse generator made and has a life expectancy of over 20 years. The circuit is a conventional ventricular-inhibited (V.V.I.) type. In vitro testing has passed all Atomic Energy Commission requirements. The present study is concerned with in vivo testing of the complete pacemaker system, by means of both myocardial and endocranial electrodes, in 20 dogs with and without induced heart block. Extensive testing for electromagnetic compatability was carried out on 1 animal with induced heart block and a special, fast-rate pulse generator. Based on studies to date, the Atomic Energy Commission has issued a license for limited clinical trial which has already begun at the collaborating institutions.     

Critical analysis of pulse generator replacement

A review of 633 pacemaker pulse generator replacements performed over 5.7 years revealed that the average life of pacemakers replaced electively (29.1%) was 24.9 months, while that of failed pacemakers (54.7%) averaged 21.6 months. Asynchronous pacers (169) lasted a mean 25.0 months and 301 demand pacers, 21.4 months. The average longevity of all pacemakers removed for all reasons was 20.7 months.Examining the evolution from (1) no clinic to (2) a routine pacemaker clinic to (3) a Pacemaker Evaluation Center with telephone analysis and peripheral clinic network, it is demonstrated that although the use of a clinic alone improved mean pacer longevity from 18.4 to 22.9 months, the evaluation center with telephone surveillance produced the greatest longevity of pacemaker units (25 units removed for failure, mean life 26.4 months). The number of electrode-related problems decreased from 15.2% to 10.7%, and the average life of pacemakers removed for these reasons increased from 5.4 to 16.7 months. Infection and erosion were also encountered less frequently (11.6% to 5.0%), and implant duration was increased (7.1 to 16.1 months). Emergency admissions decreased from 55% in 1968 to 10% in 1973, and similarly, return of symptoms dropped from 66% to 27%.We have found that a pacemaker clinic that uses a team approach reduces patient risk, alters the pattern of morbidity, and prolongs pacer longevity. Telephone surveillance may offer the greatest potential for longer pacemaker life but has numerous practical implications regarding increasing cost, time, and personnel.     

Implantation of a closed-loop stimulation in the management of medically refractory focal epilepsy: a technical note

Open-loop stimulation studies have shown varying control of seizures with stimulation of different anatomical targets. A recent multi-institutional clinical study utilizing an external closed-loop stimulation system had promising results. A novel implantable closed-loop Responsive Neurostimulation System (RNS) (Neuropace, Inc., Mountainview, Calif., USA) consisting of a cranially implanted pulse generator, one or two quadripolar subdural strip or depth leads and a programmer is under testing in a prospective clinical trial. The RNS pulse generator continuously analyzes the patient's electrocortigrams (ECoGs) and automatically triggers electrical stimulation when specific ECoG characteristics programmed by the clinician, as indicative of electrographic seizures or precursor of epileptiform activities, are detected. The pulse generator then stores diagnostic information detailing detections and stimulations, including multichannel stored ECoGs. The RNS programmer communicates transcutaneously with the implanted pulse generator when initiated by a clinician. The RNS programmer can download diagnostics and store ECoGs for review. The RNS programmer can then be used to program detection and stimulation parameters. In our current communication, we describe the selection criteria for implanting this system, the preparation of the surgical candidates as well as the surgical technique. We also present our preliminary results with 8 patients who had an RNS implanted. Seven patients (87.5%) had more than 45% decrease in their seizure frequency. The mean follow-up time in our series was 9.2 months. The implantation of a closed-loop stimulation system, in our experience, represents a safe and relatively simple surgical procedure. However, the efficacy of this new treatment modality remains to be determined in further multi-institutional, prospective clinical studies.     

Institution of Physiological Pacing Utilizing Preexisting Hardware

Six patients with ventricular inhibited pacemakers, who experienced adverse effects from loss of atrial contribution to cardiac output and loss of atrioventricular synchrony, were successfully converted to atrial demand (3 patients) and atrioventricular sequential systems (3 patients). The preexisting ventricular pulse generator was used for atrial pacing in 3 patients, and the preexisting ventricular leads were employed for atrioventricular sequential pacing in 3 patients. The advantages and potential risks of utilizing preexisting hardware for conversion of ventricular pacing into physiological pacing are discussed.     

Hardware failure in vagus nerve stimulation therapy

Summary A 20 year old male patient who had been successfully treated for epilepsy with vagus nerve stimulation (VNS) for 7 years (50% seizure frequency reduction), had experienced multiple episodes of severe hoarseness, throat pain and impaired breathing during physical exercise. As malfunctioning of the pulse generator was suspected, it was decided to replace the device. During surgery, the pulse generator was found to have broken in two, due to an unstable connection between the battery subunit and the connector subunit. With a new pulse generator seizure frequency reduction was restored. No side effects occurred. Correspondence: Kim Rijkers, M.D., Department of Neurosurgery, Maastricht University Hospital, PO BOX 5800, 6202 AZ Maastricht, The Netherlands.     

Intermuscular abdominal implantation of permanent pacemakers in infants and children.

Pacemaker implantation in infants and young children presents technical problems because of the relatively large size of the units. Various implantation sites have been employed to avoid the problems of unsightliness, migration, skin necrosis with infection, and patient discomfort. We are presenting a new technique which obviates these difficulties. The pacemaker generator is located in a space developed between the muscles and fascia of the abdominal wall. This site will accept even the largest of demand pacemakers with cosmetically acceptable results.     

Clinical trials with one type of lithium pacemaker generator

Cardiac Pacemakers, Inc. (CPI) solid-state, lithium-powered pulse generators were implanted in 100 patients by one surgeon in a twenty-eight-month period. Eleven CPI pacer generators were replaced, none due to pacer failure. Ninety-nine percent of the patients were followed for a total of 1,397.55 patient-months; 12 patients died, but no deaths appeared to be pacemaker related. The average age of the patients at the time of implantation was 72.8 years. If the warranty period of six years is achieved, the number of pacemaker generator changes required by many of the patients in this group could foreseeably be zero.     

Interference with function of unipolar pacemaker due to muscle potentials.

One hundred and seventy-three unipolar pulse generator systems were tested in 169 patients to determine the incidence of sensing of muscle potentials. One hundred and twenty-two implants in the pectoral region were suitable for assessment and 60 (49 per cent) demonstrated sensing. Ventricular-inhibited units sensed muscle potentials in 69 per cent (47 of 78), with 9 patients complaining of related symptoms. Ventricular-synchronous units sensed in 30 per cent (13 of 34) with no patient manifesting symptoms.     

Galvanic element produced by defective electrode insulation--a possible cause of abnormal pulse generator inhibition

In patients with pacemaker, abnormal inhibition with prolongation of pacing intervals may cause alarming clinical symptoms. A case is described in which high current threshold in relation to voltage threshold indicated probability of an insulation defect with current leakage. Electrograms from the electrode disclosed false signals, which had appeared after replacement of a pulse generator six months earlier. A sharp bend of the wire in the tricuspid area was shown by X-ray and was accentuated by movements of the valve. Experimentally it was demonstrated that similar potentials, sufficient to inhibit a pulse generator, can be obtained from an electrode with defective insulation. A galvanic element forms between the metals of the electrode tip and the non-insulated cable, and potential variations are elicited by movement of the wire.     

High-intensity focused ultrasound for ex vivo kidney tissue ablation: influence of generator power and pulse duration

BACKGROUND AND PURPOSE: The therapeutic application of noninvasive tissue ablation by high-intensity focused ultrasound (HIFU) requires precise physical definition of the focal size and determination of control parameters. The objective of this study was to measure the extent of ex-vivo porcine kidney tissue ablation at variable generator parameters and to identify parameters to control lesion size. MATERIALS AND METHODS: The ultrasound waves generated by a cylindrical piezoceramic element (1.04 MHz) were focused at a depth of 100 mm using a parabolic reflector (diameter 100 mm). A needle hydrophone was used to measure the field distribution of the sound pressure. The morphology and extent of tissue necrosis were examined at generator powers of up to 400 W (P(el)) and single pulse durations of as long as 8 seconds. RESULTS: The two-dimensional field distribution resulted in an approximately ellipsoidal focus of 32 x 4 mm (-6 dB). A sharp demarcation between coagulation necrosis and intact tissue was observed. Lesion size was controlled by both the variation of generator power and the pulse duration. At a constant pulse duration of 2 seconds, a generator power of 100 W remained below the threshold doses for inducing a reproducible lesion. An increase in power to as high as 400 W induced lesions with average dimensions of as much as 11.2 x 3 mm. At constant total energy (generator power x pulse duration), lesion size increased at higher generator power. CONCLUSIONS: This ultrasound generator can induce defined and reproducible necrosis in ex-vivo kidney tissue. Lesion size can be controlled by adjusting the generator power and pulse duration. Generator power, in particular, turned out to be a suitable control parameter for obtaining a lesion of a defined size.