Phrenic nerve pacing of the quadriplegic patient

J THORAC CARDIOVASC SURG 1990;99:35-40

Phrenic nerve pacing of the quadriplegic patient Phrenic nerve pacing can be used to free a quadriplegic patient from ventilatory dependency. During a 6-year period (1982 to 1988), 23 patients with an age range of 17 to 63 years (mean 31 years) underwent implantationof a phrenic nerve pacemaker because of ventilatory dependency resulting from quadriplegia. Fourteen patients bad a unilateral phrenic nerve implant and nine bad a bilateral implant. The time from injury to implantation was 12 to 16 weeks. The site of implantation was the cervical phrenic nerve in 13 patients and the thoracic phrenic nerve in 10 patients. During the past 24 months, onlya transthoracic approach has been used. The indication for pacing was failure to be weanedfrom ventilatory support in aU patients. Failure to stimulate the phrenic nerve at implantation was noted in three patients, despite preoperative testing indicating an acceptable respome. There were no deaths, and minor complications developed in three patients. FoUow-up is available in all patients: Eight patients are completely free from the ventilator, nine patients are in markedly improved condition but require the ventilator at night; three patients are in moderately improved condition; and three patients had no response. Three patients required reexploration for component failure from 6 weeks to 18 months after implantation.

Joseph I. Miller, MD, James A. Farmer, PA (by invitation), WilliamStuart, MD (by invitation), and David Apple, MD (by invitation), Atlanta, Ga.

Diaphragmatic pacing by phrenic nerve stimulation has a history dating back hundreds of years. The shortterm effects of external stimulation were well demonstratedbythe tum of the century;however, clinical applications were not available until the development of modem pacemaker technology. Current concepts in surgical technique and equipment development are largely attributedto Dr. WilliamGlennand hispioneering efforts at YaleUniversity.' Historically, Caldanf wasthe firstto note movement of the diaphragm with phrenic nerve stimulation in 1786. In 1873, Hufeland' proposed treatmentof asphyxia neonatorum with phrenicnervestimulation, and in 1898 Puchenne noticed that the phrenic nerve couldstimulatenormal respiration. I In 1968, Judsonand Glenn" first reported that a phrenic nervepacemaker had been implanted in a patient for chronic obstructive pulmonary disease. In 1972, Glenn and colleagues" reported the first pacemaker implant in a From the Joseph B. Whitehead Department ofSurgery, Division of Cardio-Thoracic Surgery, Emory University School ofMedicine, Atlanta, Ga. Read atthe Sixty-ninth Annual Meeting ofThe American Association for Thoracic Surgery, Boston, Mass., May 8-10,1989. Address for reprints: Joseph I. Miller, MD, 25 Prescott S1. NE, Atlanta, GA 30308. 12/6/16328

quadriplegic patient with ventilatory dependency. Since that time,phrenicnervepacinghas beena standard techniquefor treatingventilatory insufficiency in selected patients. Interruptionofthe motorneuronsofthe phrenicnerves associated with quadriplegia is usually the result of trauma to the spinalcord abovethe level of the sixthcervicalvertebra (C6). Occasionally, it may be from tumor invasion, radiation injury,hemorrhage, infarction, syringomyelia, and certain demyelinating diseases.v? Interruption of the neurotransmission in the spinal cord may be partial or complete. A paralyzed diaphragm can be electronically stimulatedif the lowermotor neuronsand the phrenicnerves are intact and their cell bodies in segments C3, C4, and C5 of the spinal cord are viable. Indications for phrenic nerve pacing include (l) idiopathic central alveolar hypoventilation, (2) organic lesions of the brain stem, (3) lesions of the cervical cord, (4) certain neuromuscular diseases, and (5) possible chronicobstructive pulmonary disease," In this report,we deal with lesions of the cervical cord resulting in quadriplegia. Indications for phrenic nerve pacing in quadriplegia are (1) respiratory paralysis necessitating artificialventilationfor morethan 1 month, (2) a viablephrenicnerve, (3) response ofthe diaphragmto electrical stimulationon testing, and (4) normalcerebralfunctionofthe patient," 35

3 6 Miller et al.

( Fig. 1. Dotted line illustrates skin incision over second intercostal space with planned resection of second costal cartilage.

Patients and methods This report details our experience with 23 patients with quadriplegia who underwent implantation of a phrenic nerve pacemaker between 1982 and 1988. Nineteen patients were from the Shepherd Spinal Center in Atlanta, Georgia, and four were patients of the Emory University Affiliated Hospital System. The Shepherd Spinal Center was founded in 1975 and is the largest rehabilitation hospital dedicated solely to spinal cord injuries and paralyzing disorders in the United States. The center has an average of 375 admissions per year. Approximately 250 patients are admitted for a full rehabilitation program, and approximately 115 of this group will be admitted to a full program for quadriplegia. Our 23 patients represent 4% to 5% of the total quadriplegic patient population seen during the period of study. The age range of the patients was 17 to 63 years, with a mean of 31 years. There were 10 men and 13 women. The causes of the quadriplegia were trauma in 21 patients and demyelinating disease in two patients. There were 14 unilateral implants and nine bilateral implants. The level of quadriplegia was Cl in two patients, C2 in five patients, C3 in nine patients, C4 in seven patients, and C5 in two patients. The surgical approach consisted of a cervical approach in 13 patients and a transthoracic approach in 10 patients. All bilateral cervical approaches were performed at the same time. Bilateral transthoracic implants were performed at staged intervals of 2 weeks. Surgical technique. The cervical implant technique has previously been reported by Glenn, Hogan, and Phelps." The technique basically consists of a small 2 em incision overlying the scalene triangle with lateral traction of the scalene fat pad and identification of the phrenic nerve as it crosses the anterior scalene muscle. A unipolar phrenic nerve electrode is passed under the phrenic nerve and attached with 3-0 silk sutures to the underlying scalene muscle. The lead is tunneled over the clavicle, and an infraclavicular incision is made approximately 2 ern

The Journal of Thoracic and Cardiovascular Surgery

below the clavicle in the midclavicular line. A pocket is created that will accommodate the radio receiver unit and the anode ground electrode. The technique for transthoracic implantation of the phrenic nerve pacemaker system has been modified from that originally described by Glenn so that it requires only one incision when a transthoracic approach is used. A 5 to 7 ern transverse incision is made overlying the second costal cartilage and rib (Fig. 1). The incision is extended down to the costal cartilage and rib surface. The second costal cartilage is resected in toto, and the pleural space is entered. A small pediatric retractor is placed into the wound. Ventilation is achieved by the indwelling tracheostomy tube. The lung is packed off with two pads, both superiorly and inferiorly (Fig. 2). Two traction sutures of 2-0 silk are taken above the phrenic bundle, approximately 1 em inferior to the sternal edge. These are elevated and attached to hemostats, so that the pericardium is lifted superiorly. The phrenic nerve can easily be identified along the anterior surface of the pericardium. On the right side, the ideal site for implantation isjust inferior to the junction of the superior vena cava with the right atrium. On the left side, the site of implantation is approximately at the levelof the left main pulmonary artery as it crosses out from the pericardial reflection. Once the phrenic nerve is identified, two parallel incisions are made on each side of the phrenic nerve. The entire phrenic nerve bundle, consisting of artery, nerve, and vein, is gently lifted off with a right-angle Gemini clamp. A 0 silk ligature is placed under the phrenic nerve. A unipolar phrenic nerve electrode is passed with the toe of the electrode coming from below, so that that entire phrenic bundle lies within the If-shaped bend of the phrenic nerve electrode. The electrode is affixed to the pericardium with ligatures of 3-0 silk. At the lateral portion of the thoracic incision, a battery pocket is created in the prepectoral plane. An area of approximately 5 em? is needed to implant the radio receiver unit. The electrode is affixed to the radio receiver unit, and the anode plate connecter pin is inserted into the receiving unit connector. The excess wire is tied and placed in the Teflon bag that is supplied with the implant system. The receiver unit is implanted with the copper coil facing outward, and the anode plate is placed facing outward, but not in contact with the receiver unit. The anode plate is isolated by sutures from the receiving unit, and the wound is closed in the usual fashion (Fig. 3). This modification necessitates only one incision and provides for better placement of the antenna. Selection of patients Assessment ofphrenic nerve viability. Phrenic nerve pacing is indicated in quadriplegia if respiratory paralysis, either partial or complete, has necessitated ventilatory assistance for at least I month and is stable; the phrenic nerves are viable; the diaphragm responds well to electrical stimulation; and cerebral function is normal or nearly normal," When the patient has recovered from the acute effects of the spinal injury and is in stable condition, the integrity of the phrenic nerves is investigated. Phrenic nerve viability is initially tested by percutaneous electrode stimulation I month after the injury, and the test is repeated before electrode implantation. In general, all implant operations have been performed between 12 and 16 weeks from the date of the original injury. This length of time has been established to see if there is any return of function of a previously damaged nerve. Phrenic nerve viability is tested by placing the patient on a fluoroscopic table and measuring the excursion of each hemidiaphragm during voluntary ventilation. A normal diaphragm

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Phrenic nerve pacingin quadriplegia

Number 1 January 1990

37

Fig. 2. Viewthrough second intercostal space with lung packed off and unipolar electrode placed beneath phrenic nerve. in the supine position will descend approximately 5 to 8 em during maximum voluntary inspiration. The status of the phrenic nerve is subsequently tested by applying an electrode stimulus to the nerve from outside the neck. Transcutaneous phrenic nerve stimulation is achieved by stimulating the phrenic nerve at its motor point in the neck and sensing the diaphragm muscle action potential with skin cutaneous electrodes at the ipsilateral eighth intercostal space," To be sure that there are no false negative responses, we continuously monitor the patient's condition fluoroscopically during phrenic nerve stimulation. The stimulator delivers impulses of I msec duration at a rate of I impulse per second at a current of I to 10 mA. I.8 If the nerve isviable, brisk contractions will be observed fluoroscopically and recorded on the oscilloscope. Evidence of phrenic nerve stimulation on application of percutaneous stimulation is a vigorous contraction of the hernidiaphragm visible at the costal insertion of the muscle, in addition to fluoroscopic confirmation. Nonviability of the lower motor neurons is indicated by no response of the diaphragm. Vigorous contractions with good excursions greater than 5 cm indicate a viable intact phrenic nerve. A slight contraction of the hemidiaphragm suggests that some of the motor neurons are still viable. As Glenn and Phelps! indicated, if there is any doubt about viability, the nerve should be exposed surgically and stimulated directly. During surgical implantation, the phrenic nerve is always directly stimulated and monitored with a fluoroscope. Site ofimplantation. Our initial implant operations were all performed through the cervical approach, as originally described by Glenn, Hogan, and Phelps.' After the published reports by Glenn's group" in 1986 about the transthoracic approach and its advantages, we gradually began to perform the transthoracic approach and now deem it the approach of choice and preferred site of implantation. In the thorax, the phrenic nerve is a continuous single trunk. By implanting in the thorax, one can achieve full potential of stimulation of the phrenic nerve. The phrenic nerve pacing system consists of a radio receiver unit, a unipolar or bipolar electrode, an anode ground plate, a radio antenna, and an external radio transmitter. These components have previously been described in detail," The unipolar

Fig. 3. Complete implanted phrenic nerve pacemaker system .with unipolar electrode, radiofrequency receiver unit, and anode plate. electrode is generally chosen because of the ease of insertion. The only absolute contraindication to a unipolar phrenic electrode is the prior implantation of another electronic device, such as a cardiac pacemaker, which may experience interference from the electrical discharge of a diaphragm pacemaker. In such cases, a bipolar phrenic nerve electrode must be used.

Results Twenty-three patients underwent phrenic nerve implantation. There were 13 unilateral implants and 10 bilateral implants. Cervical bilateral implants were performed in one stage and bilateral transthoracic implants were performed as a staged procedure 2 weeks apart. Operative time was approximately 45 minutes to 1 hour per side, regardless of which surgical approach was used. Complications were observed in six patients. In three patients the diaphragm failed to pace at the time of surgical exploration. Each had initially paced on percutaneous stimulation before the surgical procedure. All three of these failures occurred within the first 15 implants. Until this time we had used the original method described by Glenn and his associates' at Yale, which involvesonly oscilloscopic monitoring. In each of the patients, the action potential of the nerve appeared to be adequatefor phrenic nerve implantation. However, at the time of surgical exploration by direct stimulation of the nerve, we could not get the diaphragm to pace. There was slight diaphragmatic movement of approximately 1 em in one patient, but we did not see the usual diaphragmatic excursion of 5 to 8 em in any patient. When the third episode occurred, each approximately 2 years apart, we started to combine fluoroscopic and oscilloscopicmonitoring of phrenic nerve

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3 8 Miller et al.

stimulation. Since then, no false positive responses have occurred. Significant pneumonia developed in three patients but cleared in all of them. There were no hospital deaths. All 23 patients were available for follow-up. Results were classified as follows: Excellent-The goal of complete ventilatory independence was achieved Good-A significant gain was achieved from pacing, but another mode of support, generally the respirator, was also required Poor-Ventilatory support was required, and the pacing was not able to sustain time off the respirator

According to these criteria, eight patients required no ventilatory support, nine patients showed marked improvement but required night ventilation, three patients showed moderate improvement, and three patients showed no response. Two patients have subsequently died at home 12 months after undergoing implantation. The exact cause of death is unknown. Once the pacemaker is implanted, the conduct of phrenic nerve pacing and training of the phrenic nerve requires considerable experience and time on the part of the physician, patient, and family. There is a 2-week wait after implantation to allow edema around the phrenic nerve to subside before pacing is begun. The patient is then taken to the fluoroscopic suite in the radiology department and the pacing threshold to stimulate the diaphragm is measured. The amount of diaphragmatic excursion is measured, and the pacing threshold is set to achieve 80% to 85% of diaphragmatic excursion. The general start-up values are a pacing threshold of 1.5 to 2 rnA, a pulse interval of 40 msec, and a respiratory rate of 10 to 12 breaths/min. The lowest value that we have seen on initial implantation has been 1 rnA and the highest, 3.2 rnA. Values for arterial blood gases, forced vital capacity, and inspiratory rate are measured. The vital capacity is measured four times a day for the next month, while training of the phrenic nerve begins. Adjustments of the stimulation frequency, respiratory rate, and current amplitude will be necessary to obtain maximum ventilation, but one should always try to keep the electrical charge to the tissue as low as possible, to avoid diaphragmatic fatigue. As originally noted by Glenn, Hogan, and Phelps," the current amplitude should never be set at supermaximal, the stimulus frequency higher than 25 Hz (40 seconds), or the respiratory rate faster than 16 breaths/min. After initial stimulation thresholds, 2 to 3 months is required to train the phrenic nerve to achieve the desired goal of pacing of 8 to 12 hours. In general, a 12-hour period of time can be achieved, although in certain patients a maximum of only 8 hours can be achieved before diaphragmatic fatigue occurs. The patient is discharged ap-

proximately 6 weeks to 2 months after implantation. At that point, the phrenic nerve can be paced for between 4 and 6 hours on each side in the majority of patients with unilateral implants. The remaining training of the phrenic nerve is done at home by parents or trained personnel who are familiar with the phrenic nerve apparatus. When pacing parameters have been selected and initial threshold and maximal termination of diaphragmatic motion obtained, pacing in the quadriplegic patient is begun at 5 minutes an hour while the patient is awake, from 7 AM to 7 PM. The sides are alternated. Measurement of vital capacity at the beginning and the end of each pacing cycle is measured. A decrease of vital capacity of more than 25% at the end of the cycle compared with the beginning indicates potential diaphragmatic fatigue. The ultimate goal is to pace each hemidiaphragm for 12 hours, which results in ventilatory independence. We have used the alternating method of pacing one side for 8 to 12 hours and then pacing the other side for 8 to 12 hours while allowing the alternate side to rest. We have not adopted the use of uninterrupted simultaneous pacing of both hemidiaphragms with low-frequency stimulation of 7 to 8 Hz and a respiratory rate of 5 to 9 breaths/min, as now advocated by Glenn and his associates." because of the increased expense of the component and apparatus to the patient of approximately $15,000 to $22,000. We have had three episodes of component failure in 23 patients, at 6 weeks, 3 months, and 2 years from the date of implantation. In each patient, the malfunctioning part was the implanted radio receiver. It completely stopped pacing in two patients and paced only intermittently in one patient. All three patients underwent reexploration, the receiver unit was replaced, and satisfactory pacing was reestablished.

Discussion The successful achievement of diaphragmatic pacing in quadraplegia requires appropriate preoperative selection of candidates, the assessment of respiratory center function, determination of phrenic nerve viability, and diaphragmatic strength with lung mechanics and gas exchange. Meticulous surgical technique is a sine quo non to achieve an excellent result. Contraindications to diaphragmatic pacing, as originally outlined by Glenn, Hogan, and Phelps,? consist of nonviable phrenic nerves in which there has been injury to the anterior hom cells of C3 through C5 and progressive neurologic disease. There may be primary diaphragmatic weaknesses as a result of myopathies involving the diaphragm, flattening of the diaphragm from air trapping, and fatigue of the diaphragm from excessive ventilatory loads. In addition, poor lung compliance because of

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Phrenic nerve pacingin quadriplegia 3 9

Table I. Pacing schedules for children and adults'

Side paced

Unilateral Bilateral, simultaneously Bilateral, alternate sides Bilateral, simultaneously

Status of diaphragm

UPorP P UPorP UPorP

Time paced

Time paced (HR/23 HR)

RR (breaths/min)

Part time Part time Full time Full time

9-12 8-18

10-12

12 each side 24

8-12 10-11 5-9

Optimal pulse frequency (msec)

40-70 50-100 40-70 130-150

HR, Heart rate; RR, respiratory rate; UP. unparalyzed; P, paralyzed.

severe parenchymal lung disease or significant thoracic cage deformities is also a contraindication to phrenic nerve pacing. Certain precautions must be taken with diaphragmatic pacing": 1. Diaphragmatic pacing interferes with demand cardiac pacing. 2. A permanent tracheostomy is necessary to obtain adequate ventilation during pacing. 3. The patient's compliance and intelligence and the family's support are necessary. 4. A positive-pressure ventilator must always be available as a back-up. 5. An apnea alarm should be available in all cases. 6. A minimum pacing threshold to accomplish diaphragmatic excursion at 80% to 85% of measured excursion should be used. 7. Unilateral stimulation should not be for more than 12 hours. 8. Sedation should be avoided during pacing in all patients. The pacing schedule for adults is given in Table I. We have used the bilateral alternating side technique with stimulation of up to 12 hours on each side. Without a great amount of time, effort, and financial resources,a successfuloutcome will not be achieved. We havecompared our seriesof23 patients with 20 of Glenn's quadriplegic patients? who underwent diaphragmatic pacing. His findings are similar to ours in that eight patients achieved excellent results and eight patients received good results, that is, they still required part-time ventilatory support. Diaphragmatic pacing may be unsuccessful for the following reasons'"; (1) poor selectionof cases; (2) injury to the phrenic nerves at the time of surgical exploration; (3) improper use of the pacemaker, resulting in diaphragmatic fatigue; (4) upper airway obstruction; and (5) defective apparatus. Pacing will also fail in conditions marked by progressive disease or injury to the phrenic nerve, lungs, and diaphragm. Phrenic nerve pacing in patients with quadriplegia is a useful modality when appropriate patient selection, me-

ticulous surgical technique, and appropriate phrenic nervetesting and training are completed. Excellent results can be anticipated. Long-term success depends on adequate follow-up, support of the medical and surgical team, and the dedicated care and support of the patient's family. REFERENCES 1. Glenn WL, Phelps ML. Diaphragm pacing by electrode stimulation of the phrenic nerve. Neurosurgery 1985; 17:974. 2. Caldani LM. Institutiones physiologicae venice pezzana 1786. CitedbySchecter DC.Application ofelectrotherapy to noncardiac thoracic disorders. Bull NY Acad Med 1970;46:932. 3. Hufeland CWo Deusuelec tricaein asphyxia experimentis iIIustrato. Incugurialdissent gottingne. Cited by Schechter DC. Application of electrotherapy to noncardiacthoracic disorders. Bull NY Acad Med 1970;46:932. 4. Judson JP, Glenn WL.Radiofrequency electrophrenic respiration. JAMA 1968;203:1033. 5. Glenn WL, Holcomb WG, McLaughlin AJ, et al. Total ventilatory support in a quadriplegic patientwithradiofrequency electrophrenic respiration. N Engl J Med 1972; 286:513. 6. Glenn WL, Phelps ML, Elefteriades JA, et al. Twenty years ofexperience in phrenic nerve stimulation to pacethe diaphragm. PACE 1986;9:789. 7. Glenn WL, Hogan JF, Phelps ML. Ventilatory support of the quadriplegic patient with respiratory paralysis by diaphragmatic pacing. Surg Clin North Am 1980;60:1055. 8. ShawRK, Glenn WL, HoganJF, et al. Electrophysiologicalevaluation of phrenic nerve function in candidates for diaphragm pacing. J Neurosurg 1980;53:346. 9. Glenn WL, Hogan JF, Oloke JS, et al. Ventilatory support by pacing ofthe conditioned diaphragm in quadriplegia. N Engl J Med 1984;310:1150. 10. Marcy TW, 010ke JS. Diaphram paging forventilatory insufficiency. J Intensive Care Med 1987;2:345. Discussion Dr. John A. Elefteriades (New Haven, Conn.). Dr. William Glenn, as was mentioned, pioneered phrenic nerve pacing at Yale, and wehave been continuing the work theresince his retirement. In all, we have implanted 84 phrenic pacemakers at

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Yale. Our longest term for part-time pacing is now 19 years and for full-time pacing, 16 years. Thirty-two of the operations were done for complete quadraplegia. Initially we used unilateral pacing and subsequently we switched to bilateral pacing with alternating sides. However, what we found was that long-term survival in quadraplegic patients was dependent on freeing them completely from the ventilator, because the positive-pressure ventilator always had the inherent problems of infection, tracheal damage, and death from sudden disconnection. We found continuous stimulation of both hemidiaphragms simultaneously to be the most physiologic mode of pacing. We have compared results in patients whose phrenic nerve was conditioned to pace at a low pulse train frequency with those who were not conditioned in this way. Only one of seven "unconditioned" patients is now alive after a mean duration of pacing of 32 months. By contrast, all 12 of the "conditioned" patients, in whom the pacing frequency was about 8 Hz, were able to achieve full-time pacing and are currently alive. This demonstrates the beneficial effect of preconditioning the diaphragm to resist fatigue by lowering the electrical stimulation frequency. The average follow-up on those 12 patients is now 48 months. I have a number of questions for the authors. What was the reason for unilateral rather than bilateral pacing in some patients? Dr. Miller. The answer to that was failure of the nerve to stimulate on the side not implanted. On percutaneous stimulation and also on direct stimulation, we did not implant if we could not stimulate the nerve. Dr. Elefteriades. Some of your patients had an intact nerve at preoperative testing but failure to pace at operation. What was the reason for that? Dr. Miller. I don't know the reason. In the first group, we used only oscilloscopic monitoring without fluoroscopy. The failures occurred approximately 18 months apart in the study, and after the third one occurred we began using both oscilloscopic and fluoroscopic monitoring on percutaneous testing. Dr.Elefteriades. In a few patients function has been restored several months after the injury. Twelve weeks seems a bit early to initiate pacing. Have you had that experience at all? Dr. Miller. We have seen an occasional return of function. Generally, if function has not returned by 4 months, we don't believe it will return. I might reply to your one other question. The reason we have not used bilateral simultaneous pacing is that the cost of the apparatus is an additional $15,000 to $22,000. Also, the smaller radiofrequency transmitter is easier to attach to the wheelchair, which also must accommodate a portable ventilator. Dr. Michel N. I1bawi (Chicago. Ill.). We have used phrenic nerve pacing for a variety of conditions in 34 pediatric patients. The majority (26 or 76%) had central hypoventilation. In five (15%), quadraplegia caused by trauma was the etiologic factor. Our surgical techniques and preoperative evaluation are similar to those described by the authors. However, we differ from the authors in the sense that we use a low-frequency ventilation, which we found from both our clinical and experimental work to be much less harmful to the phrenic nerve and to be helpful in conditioning the diaphragm

Thoracic and Cardiovascular Surgery

for prolonged pacing. Thus we elect to use long interpulse intervals of 95 msec, very short inspiratory time, and moderate respiratory rates. The results in the patients with central hypoventilation have been gratifying, inasmuch as we have been successful in the majority. However, in quadraplegic patients the results are not as good. There was a failure rate of around 40% in these patients, probably because of preexisting, subclinical phrenic nerve disease. Dr. Miller, have you tried using very long interpulse intervals and low-frequency pacing rather than the high-frequency pacing that you mentioned? Dr. Miller. No, we have not. We have used only the parameters presented. Dr. I1bawi. We have faced component failure, the most important of which was receiver failure. Did you encounter similar problems? Dr. Miller. Yes, we had three receiver failures in a group of 23 patients. All three receivers were replaced and successful pacing was reestablished. Dr.Ernst Wolner (Vienna. Austria). My colleagues, Thoma and Holle, and I have treated 16 patients at Vienna University, II for spinal cord injury with a respiratory pacemaker and four for lower spinal cord injuries with a leg pacemaker. We use a device similar to yours, with an externally controlled power unit with high-frequency energy transmission, and also a telemetric control of the pacemaker tha t allows us to change the stimulation parameters of the pacemaker. There is some difference between our system and yours with regard to the top of the electrodes. Four of these small electrodes are attached to the nerve by microsurgical methods, and these four electrodes allow us to switch the electric stimulation through the nerve with a computerized program to prevent nerve fatigue. Like you, we developed a special clinical program for patients with spinal cord injuries. This special program ends with closure of the tracheostoma after about 3 months, which is comparable to your follow-up program. Of these II patients with high spinal cord injury, three died, two of pulmonary embolism and one of sepsis. Of the other eight patients, six are at home with a closed tracheostoma. The overall experience with this method is now 35 patient-years. I have two questions for you: All our patients were operated on through the transthoracic approach. What is your opinion about neck approach versus transthoracic approach for the electrodes? Dr. Miller. The transthoracic approach is a much simpler approach. It is quick and, as pointed out by Dr. Glenn, it avoids anomalies of the phrenic nerve in the neck, which are present in 15% to 25% of individuals. Dr. Wolner. Are you able to wean all patients with unilateral phrenic stimulation from the respirator? Dr. Miller. The majority of patients who had lesions at the C3-C4 level and who had a unilateral implant were able to be weaned. If the injury was at C2 or above and we could stimulate only one side, we could not wean the patient from the ventilator completely.