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Bifocal Pacemakers
COMMUNICATIONS TO THE EDITOR
period of study whether or not these two failures were unusual deviations from the norm. Seymour Furman, M.D.
Bronx, New York
Bifocal Pacemakers To the Editor: I am prompted to write by our recent experiences with the American Optical Company Bifocal pacemakers. Because of the publication in Chest of a communication by Castillo and colleagues, and a laudatory editorial by Dr. Harken in the April, 1971 issue of Chest, I feel that Chest bears a special responsibility for the use of the pacemaker itself, as no other full length reports of its use exist. The implantation of this unit may be characterized by a problem of self-inhibition which has not been seen in similar fashion in any pacemaker manufactured heretofore. Improper placement of the atrial electrode or late postimplant movement of that electrode, even if initially well placed, may produce false inhibition of ventricular stimulation. The atrial stimuli in this unit are virtually continuous. The ventricular stimulating circuit operates in the ventricular inhibited (demand) mode. Consequently, if the atrial stimuli are sensed by the ventricular electrode, the pacemaker is driven to inactivity and returns the patient to an unprotected state of ventricular activity. If the atrial stimuli are adequate to drive the atrium which in turn drives the ventricle, then little physiologic effect occurs. In our patient the atrial electrode moved from a position adequate to one inadequate to stimulate the atrium., but from which the ventricular stimulator was inhibited. The patient had no pacemakerinduced activity of either atrium or ventricles, and was returned to the unprotected state. Castillo and co-authors briefly alluded to this theoretic possibility; nevertheless, the problem has now become a reality and one which should be carefully pointed out as a distinctly possible complication in this new type of pacemaker. In our patient, electrode revision returned the pacemaker to normal function. Two of the six pulse generators we implanted underwent early battery failure and failed within three months of use. The serial numbers suggested that they were manufactured at almost the same time. While it is possible that a single problem not indigenous to the bifocal pacemakers affected both units, I have no way of knowing this. As the manufacturer has recently offered the bifocal pacer for more general sale, I believe that the profession is due a recounting of the clinical experience with this unit. We should be reassured concerning its safety and efficacy and know over a prolonged
o
To the Editor: The possibility of false inhibition by the electrotonically conducted atrial impulse as it has been reported by Dr. Furman may occur with bifocal pacing when the atrial and the ventricular pairs of electrodes are less than one and one-half inches apart. It is important, therefore, that the atrial pair of electrodes be placed as far as possible from the tricuspid valve and, thus, prevent the possibility of its entry into the ventricular cavity. Between October, 1969 and February, 1972, 85 bifocal pacemakers made by our Research Division have been implanted for the purpose of clinical evaluation. Units which failed were returned and analyzed. Most of the failures, including the two reported by Dr. Furman, were traceable to a defective lot of batteries, which has also been reported as a cause of premature failures in commercial pacemakers made by other manufacturers. The chance of this type of defect occurring again has been eliminated by the battery manufacturer through a design improvement. The other causes of failure were random failure of components, associated with pacemakers made for research and in no way indicative of any defect in the design or concept of the bifocal pacemaker. These figures are given below:
Bifocal pacers implanted Returned after removal from patient for variety of reasons but functioning properly Returned after removal from patient with depleted battery (battery exhaustion) Returned after removal from patient because of failures due to defective lot of batteries Returned after removal from patient due to epoxy failure Returned after removal from patient due to defective output capacitor Returned after removal from patient due to defective glass capacitor
No. Pacers 85
Average Time (Months)
12 4
19
6
6
2
8
1
7
1
The dramatic improvements seen in some patients who needed the physiologic benefits obtainable only by bifocal pacing justifies the use of this modality of pacing, in spite of the increased pacemaker size and the additional skills needed when implanting two sets of electrodes instead of one.
237
period of study whether or not these two failures were unusual deviations from the norm. Seymour Furman, M.D.
Bronx, New York
Bifocal Pacemakers To the Editor: I am prompted to write by our recent experiences with the American Optical Company Bifocal pacemakers. Because of the publication in Chest of a communication by Castillo and colleagues, and a laudatory editorial by Dr. Harken in the April, 1971 issue of Chest, I feel that Chest bears a special responsibility for the use of the pacemaker itself, as no other full length reports of its use exist. The implantation of this unit may be characterized by a problem of self-inhibition which has not been seen in similar fashion in any pacemaker manufactured heretofore. Improper placement of the atrial electrode or late postimplant movement of that electrode, even if initially well placed, may produce false inhibition of ventricular stimulation. The atrial stimuli in this unit are virtually continuous. The ventricular stimulating circuit operates in the ventricular inhibited (demand) mode. Consequently, if the atrial stimuli are sensed by the ventricular electrode, the pacemaker is driven to inactivity and returns the patient to an unprotected state of ventricular activity. If the atrial stimuli are adequate to drive the atrium which in turn drives the ventricle, then little physiologic effect occurs. In our patient the atrial electrode moved from a position adequate to one inadequate to stimulate the atrium., but from which the ventricular stimulator was inhibited. The patient had no pacemakerinduced activity of either atrium or ventricles, and was returned to the unprotected state. Castillo and co-authors briefly alluded to this theoretic possibility; nevertheless, the problem has now become a reality and one which should be carefully pointed out as a distinctly possible complication in this new type of pacemaker. In our patient, electrode revision returned the pacemaker to normal function. Two of the six pulse generators we implanted underwent early battery failure and failed within three months of use. The serial numbers suggested that they were manufactured at almost the same time. While it is possible that a single problem not indigenous to the bifocal pacemakers affected both units, I have no way of knowing this. As the manufacturer has recently offered the bifocal pacer for more general sale, I believe that the profession is due a recounting of the clinical experience with this unit. We should be reassured concerning its safety and efficacy and know over a prolonged
o
To the Editor: The possibility of false inhibition by the electrotonically conducted atrial impulse as it has been reported by Dr. Furman may occur with bifocal pacing when the atrial and the ventricular pairs of electrodes are less than one and one-half inches apart. It is important, therefore, that the atrial pair of electrodes be placed as far as possible from the tricuspid valve and, thus, prevent the possibility of its entry into the ventricular cavity. Between October, 1969 and February, 1972, 85 bifocal pacemakers made by our Research Division have been implanted for the purpose of clinical evaluation. Units which failed were returned and analyzed. Most of the failures, including the two reported by Dr. Furman, were traceable to a defective lot of batteries, which has also been reported as a cause of premature failures in commercial pacemakers made by other manufacturers. The chance of this type of defect occurring again has been eliminated by the battery manufacturer through a design improvement. The other causes of failure were random failure of components, associated with pacemakers made for research and in no way indicative of any defect in the design or concept of the bifocal pacemaker. These figures are given below:
Bifocal pacers implanted Returned after removal from patient for variety of reasons but functioning properly Returned after removal from patient with depleted battery (battery exhaustion) Returned after removal from patient because of failures due to defective lot of batteries Returned after removal from patient due to epoxy failure Returned after removal from patient due to defective output capacitor Returned after removal from patient due to defective glass capacitor
No. Pacers 85
Average Time (Months)
12 4
19
6
6
2
8
1
7
1
The dramatic improvements seen in some patients who needed the physiologic benefits obtainable only by bifocal pacing justifies the use of this modality of pacing, in spite of the increased pacemaker size and the additional skills needed when implanting two sets of electrodes instead of one.
237