Disposable in-package load test element for pacemakers

A test device for use with a pacemaker to simulate the load of a heart. The device is designed for telemetering control and includes in its circuit a magnetic reed switch which opens and closes a load circuit in response to a remotely applied magnetic field. The device is intended to be disposable and is installed in circuit with the pacemaker terminals which normally connect to the heart leads. The device as thus installed is packaged in the sterile shipping package with the pacemaker and both permit the final checking of the pacemaker within its sterile pack prior to shipment and testing of the pacemaker in preparation for implantation without the necessity of opening the sterile package to conduct the test.

This invention relates to cardiac pacemakers and, more particularly, to an 
element to be included in a sterile packaged pacemaker to permit more 
thorough testing thereof prior to surgical implantation. 
BACKGROUND OF THE INVENTION 
It is common for the manufacturers of electrical equipment to test such 
equipment before packaging and shipping the equipment to distributors, 
sales outlets, end users and the like. Such testing may include checking 
the various modes of operation of the equipment for satisfactory 
performance, proper adjustment of controls within prescribed tolerances, 
operating ranges, etc. and it may also include several hours or days of 
operation ("burn-in") to check for stability and to detect possible 
premature failure. Still other tests may involve running the equipment 
under specified overload conditions, performing tests of certain 
components or portions of individual circuits within the equipment, and 
checking for weaknesses or the presence of defective components or other 
circuit parts which may not be readily apparent from test operation of the 
equipment. It is not uncommon for others down-line in the distribution 
channel leading to the ultimate end user to perform similar tests of the 
equipment before final disposition. 
A cardiac pacemaker is a type of electrical equipment in which testing for 
proper, reliable operation is essential. Because of the nature of the use 
of a pacemaker, it is literally true that a life may be at stake if a 
pacemaker malfunctions during operation when implanted in a patient. For 
this reason, elaborate tests are performed during the manufacture of 
pacemakers to make them as reliable as possible. 
A further, relatively unique demand is imposed on pacemakers by virtue of 
their ultimate use. The pacemaker and all of its internal components must 
be surgically sterile. Thus, after manufacture and testing, the pacemaker 
is sterilized and sealed in sterile packaging, to be maintained in sterile 
condition until the packaging is removed in preparation for implantation 
of the pacemaker by a surgical team. 
An appreciation of the problem of testing an electronic component in a 
sterile package without invading the internal sterile environment of the 
component is evidenced in U.S. Pat. No. 4,605,007 of Heraly. That patent 
discloses an inner and outer container with feedthrough contacts in the 
outer container to physically contact the electrical contacts of the 
sterilized electrical component. Thus circuit connections may be 
established with the outer contacts without affecting the sterile 
condition and environment of the inner contacts that constitute part of 
the electrical component in the sterile environment. This component, 
however, is only a part of a cardiac pacemaker and is not subject to the 
problems of testing the terminal connectors and lead circuitry of an 
overal pacemaker. The provision of access to an internal, prepackaged 
electrical component which is taught by Heraly is akin to that which is 
customarily provided for testing drycells that are commonly marketed in a 
bubble pack package. A pair of small holes in the bubble pack are provided 
next to the drycell terminals so that a pair of voltmeter electrodes can 
be applied to the terminals without opening the package. Heraly adapts 
that principle to protection of a sterile environment in which an 
electrical component is packaged. 
It is generally possible to conduct certain tests of pacemakers while they 
are still enclosed within their sterile packaging. Modern pacemakers not 
only can receive programmed instructions, but they can also send back 
messages regarding the status of the pacemaker. This ability to remotely 
interrogate the pacemaker by wireless means is called telemetry. Telemetry 
can provide a readout of the various programmable functions of a pacemaker 
and an indication of the properties of certain of the pacemaker 
components. Final testing of a cardiac pacemaker is generally performed by 
the surgical team in preparation for implantation. It is common to have a 
plurality of pacemakers at hand, still in their sterile packaging, in the 
operating room at the time of final testing so that no time need be wasted 
in drawing another unit from inventory if a defect is discovered in the 
one under test. 
Heretofore it has been difficult, if not impossible, to provide a final 
test of the terminal connectors for the leads which are to be inserted in 
the patient's heart and plugged into the pacemaker for implantation, yet 
these terminal connectors constitute one of the important potential 
failure points of a pacemaker. While certain types of terminal failures 
may be detected at final telemetry testing, others cannot. For example, an 
unusually low impedance in the terminal connector circuit may suggest a 
break in insulation. However, since the terminal circuit is open prior to 
connection to the heart leads, a break in a wire leading to the terminal 
does not provide any different indication and therefore cannot be detected 
until the leads are connected to the pacemaker. Detection of such a 
failure at this points represents a setback in the surgery time schedule, 
necessitating the susbsitution of another pacemaker which requires 
duplication of the programming, testing. etc. already conducted on the 
first pacemaker. 
SUMMARY OF THE INVENTION 
In brief, arrangements in accordance with the present invention comprise a 
prefabricated until which can be temporarily installed in a circuit 
connection to the pacemaker terminals and is adapted to sterilization and 
packaging with the pacemaker. Thus the unit circuitry can be used during 
the final testing of the pacemaker by the surgical team to permit tests of 
the pacemaker terminal connectors and circuits which were not heretofore 
possible without removing the pacemaker from its sterile packaging. 
In its simplest embodiment, a unit in accordance with the present invention 
comprises a resistor in series with a normally open magnetic reed switch. 
This series circuit is placed electrically between the signal output and 
return terminals of the pacemaker. The circuit remains attached to the 
pacemaker in the sterile package. It presents no electrical load to the 
pacemaker circuits because the reed switch is in the normally open 
position. Usually a permanent magnet in the interrogation device is used 
to close a reed switch which is internal to the pacemaker. Thus the unit 
is effective in the testing of an associated pacemaker with any telemetry 
interrogation system that utilizes a magnetic field. 
When the reed switch of the unit is closed by the application of a magnetic 
field, the electrical load comprising the unit's resistor (plus the 
negligible resistance of the reed switch) is placed across the pacemaker 
terminals. Although the value of the resistor is not critical, it 
preferably approximates the load that a heart presents to the pacemaker, 
typically 300 to 500 ohms. When such a load value is used for the 
resistor, the measured data telemetered back to the interrogating device 
will be representative of data measured from a properly implanted 
pacemaker. In addition, the pacemaker connector/feedthrough terminal 
integrity may be tested. Such a device thus further improves the 
reliability and thoroughness of the testing procedure which occurs prior 
to implantation. Since it has only two electrical components, the device 
is extremely reliable. Moreover, because of its simplicity and low number 
of parts, its cost is very low. The device is designed to be discarded 
after a single use. 
Variations of the invention are designed for use with different kinds of 
pacemakers. The embodiment as just described is for use with a single 
chamber, bipolar (not inline) pacemaker). 
In another embodiment of the present invention, two series circuit paths, 
each including a single resistor and magnetic reed switch, are provided 
for connection to the terminals of a unipolar, dual-chamber pacemaker. In 
this embodiment, the distal ends of the two individual paths are tied 
together and connected to a pacemaker return contact. 
Still another embodiment of the present invention incorporates a pair of 
separate circuit paths, each including a load resistor and a magnetic reed 
switch, with both ends of these circuit paths being located for coupling 
to the terminal leads of a dual chamber, inline, bipolar pacemaker when 
the device is inserted into the female terminal configurations of the 
pacemaker. 
The circuit components of each unit are sealed within a plastic body, from 
which only the electrical lead terminals extend. The plastic body is 
configured to mate with the female terminal configuration of the pacemaker 
with which it is associated and, for units providing a pacer return 
contact, the configuration of the plastic body is such that the return 
contact is fixed in a position and attitude to contact the metal case of 
the pacemaker when the unit is inserted into the female terminal 
connectors of the pacemaker.

DETAILED DESCRIPTION OF THE INVENTION 
The following description is of the best presently contemplated mode of 
carrying out the invention. The description is not to be taken in a 
limiting sense but is made merely for the purpose of describing the 
general principles of the invention. The scope of the invention should be 
determined with reference to the attached claims. 
Implantable cardiac pacemakers of the type here involved have a housing 
which is of more or less standard size and shape for those models of 
pacemakers which are presently being manufactured. A typical pacemaker 10 
is shown in an enlarged view in FIG. 1. Such a pacemaker is approximately 
the size and weight of a conventional pocket watch. Typically the 
pacemaker 10 of FIG. 1 has a housing comprising a metal case 12 to which 
is affixed a connector top 14, usually formed of plastic. The pacemaker 10 
is shown with a pair of openings 16, 18 in the end wall 20 of the 
connector top. These openings 16, 18 are the outer ends of bores which 
extend back into the connector top and are provided to receive the 
terminal connectors of leads which extend to the patient's heart. The 
pacemaker may be single chamber or dual chamber, unipolar or bipolar, 
inline or not inline, and a test element configuration in accordance with 
the present invention may be adapted accordingly to be usable with a given 
pacemaker. 
FIG. 2 shows a particular arrangement of the present invention configured 
for a dual chamber unipolar pacemaker and corresponds to the circuit 
arrangement depicted in FIG. 4. Device 22 is shown with two wire terminal 
connectors 24, one for each of two pacer outputs, and a pacer return 
contact 26 which makes contact with the pacemaker case in the region 28 
(FIG. 1) when the unit 22 is mounted in place on the pacemaker 10. Device 
22 has a pair of cylindrical hollow rods 21 extending longitudinally from 
a base portion 30. By means of this arrangement, the rods 21 and the 
terminal connectors 24 are maintained in the proper orientation to enter 
the bores 16, 18 of the pacemaker when the device 22 is installed. Each 
cylindrical rod contains a resistor 32 and a magnetically responsive reed 
switch 34, interconnected with the return contact 26 as shown in FIG. 4. 
For the configuration represented in FIG. 5, which shows a single chamber, 
bipolar (not inline) pacemaker, wherein the return contact 26 is dispensed 
with, only one resistor and switch combination 32, 34 is present in one of 
the cylindrical rod portions 21. The other member 21 only contains a wire 
extending from the lower terminal connector 24 and completing the circuit 
to the reed switch 34. 
FIG. 3 shows a test device 36, like the device 22 of FIG. 2 except that the 
device 36 is provided with added contact elements 38 for use with a dual 
chamber, inline, bipolar pacer, such as the combination represented 
schematically in FIG. 6. In this arrangement, the return contact 26 is not 
in the circuit; it is not used electrically but is included for uniformity 
of fabrication. 
In the circuit of FIG. 5, one of the terminals 24 is the pacer output; the 
other is for the signal return. In the circuit of FIG. 6, the terminals 24 
are typically pacer output leads while the connectors 38 correspond to the 
signal return contacts where they connect into the pacemaker 10. 
FIG. 7 shows a combination 40 of a pacemaker 10 as packaged within a 
sterile pack 42, ready for shipment or for testing in preparation for 
implantation. The in-package test device 22 is shown installed on the 
pacemaker with the terminal connectors inserted into the plastic cap 14. 
The pack 42 is shown with a peripheral sealing edge 44 which surrounds the 
trapped, sterile chamber 46 in which the pacemaker 10 is maintained in a 
sterile environment. The chamber 46 typically contains a sterilizing gas 
which serves to sterilize the pacemaker and its components and to maintain 
the contents of the chamber sterile as long as the integrity of the 
package is not disrupted. The material of the pack 42 is typically of 
transparent plastic so that the pacemaker is clearly visible within the 
package. 
With devices in accordance with the present invention, faulty connector 
elements and feedthrough to internal electronics of a package pacer can be 
detected without opening the sterile package. This permits a final 
operational test of the pacemaker within its package before the unit is 
shipped. Telemetered interrogation of the packaged pacer occurs with the 
pacer under load--i.e., in circuit with the series resistor 32 of the test 
device--yet when the interrogation device is removed, the load is removed 
from the pacer circuitry upon the opening of the reed switch 34 so that 
there is no excessive battery drain between the time of manufacture and 
the time of implantation. At the other end of the pipeline, when the unit 
is prepared for implantation, the surgical implantation team can verify 
electrical functionality of the pacer by the same means before the sterile 
package is opened. 
It will be understood that the order of the elements in the series circuit 
path, the reed switch and the resistor, may be reversed, just as the 
output and return terminals 24 of the single chamber bipolar pacer of FIG. 
5 may be interchanged. 
The concept of the present invention is independent of the pacer 
manufacturer or pacer design, and is readily adaptable to different 
terminal configurations. The only requirement is that a magnetic field 
must be present to activate the reed swich during telemetered 
interrogation. However, equivalent devices providing the capability of the 
reed switch may be substituted in the test device circuit(s). For example, 
a Hall effect switch or some other proximity switch which can open and 
close an electrical path in response to a remote signal or applied field 
may be used. 
If desired, a light emitting diode (LED) or similar indicator may also be 
placed in the circuit, in series with the device as shown, thereby 
providing a simple, quick diagnostic tool which requires only the presence 
of a magnetic field to cause activation. Other variations in accordance 
with the present invention may be devised. 
Although there have been described above specific arrangements of a 
disposable in-package load test element for pacemakers in accordance with 
the invention for the purpose of illustrating the manner in which the 
invention may be used to advantage, it will be appreciated that the 
invention is not limited thereto. Accordingly, any and all modifications, 
variations or equivalent arrangements which may occur to those skilled in 
the art should be considered to be within the scope of the invention as 
defined in the annexed claims.