THE VIENNA PHRENIC PACEMAKER, LONGTERM DATA OF FAILURES

 

H. Thoma*, P.Darrington**, E.Unger*

 

*  University Vienna, Austria, Department of Biomedical Engineering and Physics

** Börgel Inc., Limburg, Germany

 

INTRODUCTION

 

The Vienna Phrenic Pacemaker System consists of extracorporal (control unit, RF transmission coil) and implanted components (electronic 8-channel implant with stimulation electrodes/1/). To avoid fatigue of the diaphragm muscle because of continous electrostimulation – 24 h per day – the so-called “roundabout-stimulation” was developed and patented /2/. The implant is powered and controlled by RF-impulse transmission from the control unit. The control unit is powered by rechargable batteries. This development was used 1982/83 for stimulation of lower extremities in 4 paraplegic patients for standing up and walking using forearm crutches. The same system was implanted in the first quadroplegic patient (level: C1/2) with paralyzed breathing in 1983, but new software for stimulation of inspiration cycle was used. Since 1980, the development of this system has not undergone relevant changes despite of some technological improvements – e.g. total metal sealing of all electronic components in 1993 /3/. Therefore it is of interest to do an analisis of relevant failures and to develop an update control unit in order to avoid such failures in future.

 

In the following we will focus on a statistic of failures of the electronic implant and the control unit. We have nearly no failures in electrodes, RF coil and 220 V power supply. Otherwise batteries and cables were exchanged routinely about once a year.

 

METHODS

 

For this paper we collected material from different sources. Patient’s data and implant failures were found in former publications. In addition, we could prove this data by auditing accounts of Medimplant Inc. Vienna – producer of the pacemaker system. The yearly check of the patients´ pacemaker is an order by law. Therefore we got excellent data concerning the functions of the pacemaker via the patient’s medical record keeping device. This documentation is done by Börgel Inc., Limburg, German representative of the Vienna phrenic pacemaker. A new control unit was developed this year.

 

In the following section detailed results of patients, the lifetime of implants and specific failures of the control unit as well as the features of the new development are presented.

 

RESULTS

 

1.      The implant

An overview of our phrenic pacemaker patients is summarized in fig. 1. Despite of these 26 registered patients one male patient was operated on in 1982 and one 6 year old boy with a lesion in the level C 0 was not registrated /4/.

 

Reimplantation was necessary 18 times. In 3 patients reimplantation was necessary 3 or 4 times, in 17 patients there was no reimplantation. In 4 patients lifetime of the implant is between 9 and 11 years. The main reason of the frequent early failures was due to the implant technology: some electronic parts were sealed only in Hysol. Implants after 1993 were totally wrapped in metal housing, the receiver RF coil protected by a ceramic ring. Up to now, there are not any failures with this updated implants. As our implants have connectors to the 8 electrodes, is the change quite similar to the cardiac pacemaker.

 

In 1990 we started a development of a 20 channel implant encapsulated by niobium. This implants were tested in animal studies (calfs) for a period of cumulative 4,5  years in Vienna and Ljubljana. No failures were observed during these tests.

 


Fig 1: patient overview, starting 1983 up to 2001

 

2.      The control unit T154S

 

Specific failures of the battery driven control unit T154S were analysed in 5 patients, lasting for cumulative 60 patient years. In fig. 2 patients were listed according to “years after implantation” (7 up to 15 years). In the process of time 3 different groups may be discussed. During the first 5 years few failures were only due to mechanic components. The most frequent failures were registered during the period of the years 6, 7 and 8. The remaining years 9 to 15 have to be discussed: on the one side the number of evaluated patients is going down, on the other, the yearly failure rate decreases unproportionally to the number of remaining patients, e.g. no registered failures in the year 11 after implantation. We may get additional informations calculating the failure rate of each patient:

 

 

 

 

 

years

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

total

 

number of patients

5

5

5

5

5

5

5

4

4

4

4

3

3

2

1

 

mechanic

housing

 

 

I

 

II

 

II

I

 

 

 

 

 

I

 

7

cable connectors

 

 

I

 

I

I

I

II

I

I

 

 

I

I

 

10

cable break

 

 

I

 

 

I

I

II

I

 

 

 

I

I

 

8

plug connection break

 

 

 

 

 

II

 

 

I

I

 

 

I

 

 

5

hardware

display

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0

switch print

 

 

I

 

 

I

II

I

I

I

 

 

 

I

 

8

power print

 

 

 

 

I

II

I

 

 

 

 

I

 

I

 

6

main print

 

 

 

 

 

I

I

 

 

 

 

 

 

I

 

3

software

eprom update

 

 

I

 

 

I

 

II

 

 

 

 

 

 

 

4

microprocessor

 

 

 

 

 

I

 

I

 

 

 

 

 

 

 

2

 

total

0

0

5

0