CLEVELAND—Actor Christopher Reeve, who has been ventilator-dependent since an accident eight years ago, has opted to use an experimental device that may soon allow him to be free of the ventilator. The new device consists of electrodes surgically implanted into the diaphragm to stimulate breathing.

A SAFER ALTERNATIVE?

Mr. Reeve is the third patient to try the device, which was developed by a Case Western Reserve University team headed by Anthony F. DiMarco, MD, and Raymond Onders, MD. Their technique, which requires only laparoscopic surgery, is expected to be safer than traditional phrenic nerve pacing, in which electrodes are inserted into the nerve itself.

The former Superman star underwent the surgical procedure on February 28. Dr. DiMarco stated in an interview that, as is usual with patients who have been ventilator-dependent for a long time, Mr. Reeve needs a 12- to 14-week period of gradual strengthening and toning of his pulmonary musculature before he can attempt to abandon the ventilator. This period typically begins about two weeks after the surgery and involves switching the patient from mechanical ventilation to diaphragm pacing for progressively longer periods each day. Within weeks of starting his postsurgical training, the actor was able to breathe on his own for several hours each day.

“Our goal is to provide something safer and less expensive than conventional phrenic nerve pacing. Our experience so far suggests that diaphragm pacing provides an overall improved sense of well-being and enables the patient not only to breathe but also to speak more normally. There are also social benefits, since in a casual setting you really can’t tell that a patient is being paced by this device,” commented Dr. DiMarco.

PACING PROCEDURE

The procedure for Mr. Reeve was the same as that used in the initial case the investigators reported last year,[1] with one exception: They are now using only suction electrodes to identify target areas in the diaphragm rather than the elaborate fine mapping technique described in that report. “One thing we are still working on is refining our method for identifying target spots for electrode placement,” Dr. DiMarco noted.

Four trocars are placed into the abdominal cavity, and a pneumoperitoneum is created (Figure 1). Suction electrodes are used to identify the two phrenic nerve motor points—the places where the phrenic nerves enter the right and left hemidiaphragms. Two stainless steel intramuscular diaphragm electrodes are inserted into each motor point. Wires from the four electrodes are brought out through the epigastric port (some slack is left to allow movement), tunneled subcutaneously to the chest, and attached to a connecting circuit. Each wire is then tunneled subcutaneously to the right subclavicular region, where the wires exit the chest wall.

Figure 1

The laparoscopic implant procedure used for diaphragmatic pacing requires insertion of four trocars into the abdominal cavity. Electrodes are inserted through these trocars into the phrenic nerve motor points—the places where the phrenic nerves enter the right and left hemidiaphragms. Adapted from DiMarco et al. Am J Respir Crit Care Med. 2002.[1]

“Recovery from the laparoscopic surgery has been incredible,” Dr. DiMarco said. “Patients are up and eating dinner by the end of the day.”

The electrodes in the diaphragm are then connected to an external four-channel electrical stimulator about the size of two decks of cards. This is programmed to produce regular contractions (“pacing”) of the diaphragm. The investigators expect to have a smaller, completely implantable radio-controlled version available within two years; this would eliminate the need for wires exiting the chest.

Dr. DiMarco reported that the first patient to use this device continues to do well after two years and maintains a maximum inspired volume of over 1,200 mL. Diaphragm pacing was not successful for the second patient, however. “There were no effects at all, and we are still trying to figure out why,” Dr. DiMarco explained. “We suspect that there were unrecognized problems in phrenic nerve conduction in this patient.”

Traditional phrenic nerve pacing requires thoracotomy and the placement of electrodes around the nerve, at an estimated cost of $60,000 for equipment plus $10,000 to $15,000 for hospitalization. The diaphragm-pacing equipment is expected to cost less than $30,000, and the laparoscopic procedure does not require hospitalization.

According to Dr. DiMarco, the method for implanting the device is fairly easy to learn and it could be available in about two years. If all goes well with the next 10 patients, Dr. DiMarco said, his group will consider marketing it, as they are legally entitled to do under their investigational device exemption. Meanwhile, they are in the process of recruiting the 25 to 35 patients needed to obtain full FDA approval.

To be a candidate for diaphragm pacing, a patient must be ventilator-dependent due to spinal cord injury but have intact bilateral phrenic nerve function. “Physicians who have patients they would like to refer for our study should first obtain bilateral phrenic nerve conduction studies,” Dr. DiMarco stated.

—Janis Kelly

Reference
1. DiMarco AF, Onders RP, Kowalski KE, et al. Phrenic nerve pacing in a tetraplegic patient via intramuscular diaphragm electrodes. Am J Respir Crit Care Med. 2002;166:1604-1606.

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