Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-08-31
2001-08-28
Evanisko, George R. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S120000
Reexamination Certificate
active
06282444
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an apparatus for killing microorganisms which may form in a biofilm on surfaces of implanted devices and, more particularly, to such an apparatus used with a cardiac stimulation device, e.g., a cardioverter-defibrillator (ICD), pacemaker or the like.
BACKGROUND OF THE INVENTION
Infections which may occur with pacemaker/ICD devices are relatively untreatable without device removal since the bacteria live in a biofilm on the device which blocks antibiotics. When the biofilm of such an implantable device becomes infected, it is almost universally impossible to treat the infection with systemic antibiotics. The standard medical procedure is to explant the device, leading to additional costs, risks and discomfort to the patient.
The reason that device infections cannot be treated by systemic antibiotics is that the biofilm protects the bacteria from systemic antibiotics and allows them to tolerate levels of antibiotics that are several orders of magnitude above that which can safely be given to a patient.
To overcome this tolerance to antibiotics, the use of electrical fields to kill bacteria in the biofilm has been investigated and discussed in the prior art. Exemplary patents include U.S. Pat. Nos. 5,312,813; 5,409,467; and 5,462,644.
SUMMARY OF THE INVENTION
The present invention is directed to an apparatus for treating an infection which may occur in the biofilm which surrounds an implanted cardiac stimulation device, e.g., a cardioverter-defibrillator (ICD) or a pacemaker. Such infections are relatively untreatable by conventional antibiotics treatments. Thus, explanting of the implanted devices may be required. Accordingly, the present apparatus provides an electrical treatment that enables a biocide, i.e., an antibiotic, to successfully treat the infection within the biofilm and thus avoid the necessity to explant the device. Furthermore, the present invention provides this electrical treatment in a manner to not interfere with the stimulation pulses of the cardiac stimulation device.
A biofilm is a conglomerate of microbial organisms imbedded in a highly hydrated matrix of exopolymers, typically polysaccharides and other macromolecules. Unlike planktonic organisms which are relatively susceptible to antibiotics, the structural matrix established during biofilm formation can make the colonizing cells able to withstand normal treatment doses of a biocide. However, the application of a relatively low current on the order of perhaps 10-100 microamperes per square centimeter is sufficient to allow the antibiotics to penetrate the biofilm and destroy the bacteria.
In one study (ASAIO Journal 1991; 38:M174-M178, Prevention and Control of Bacterial Infections Associated with Medical Devices by Khoury et al.), the curve presented in
FIG. 1
was generated. The solid line shows only a minimal reduction in the concentration of living biofilm cells after a dozen hours of the application of an antibiotic. On the other hand, by applying a low current, the number of living biofilm cells dropped by one order of magnitude every two hours.
The present invention provides an electric current to treat an infection in the surrounding biofilm of an implanted cardiac stimulation device, e.g., a cardioverter-defibrillator (ICD), pacemaker or the like. More specifically, a first coil, i.e., the SVC coil, is implanted in the region of the right atrium and a second coil, i.e., the RV coil, or other suitable electrode is implanted in the right ventricle (RV). Currents are delivered between the RV coil and from the SVC coil to the conductive case of an implanted cardiac stimulation device to treat the infection.
Currents on the order of 15 microamperes per square centimeter are considered therapeutic for this process. Due to the heterogeneities of the current in an ICD surface, for example, one must be conservative in estimating the currents. It is desirable to assume a very cautious position, that the current density in the device housing varies by 100:1 from the highest to the lowest current density. To simplify the calculations, it is further assumed that the lowest current density is {fraction (1/10)} of the average. Thus, an average current density of 150 microamperes per square centimeter is needed to guarantee the minimum requirement for purposes of the invention. Assuming a device having a 70 cm
2
surface area, this results in a treatment level of about 10 ma for the average current to the device. This average current is preferably maintained for about 10 hours (see
FIG. 1
) to achieve a maximum therapeutic benefit. However, a 10 ma current from an implantable coil to the case of a cardiac stimulation device is also capable of pacing the heart and thus care must be taken to not induce an arrhythmia. Accordingly, the present invention supplies an infection control current in a manner to not interfere with either the natural pacing of the heart or pacing pulses supplied or sensed by an implanted cardiac stimulation device. Accordingly, the risk of causing an arrhythmia is minimized.
In a first embodiment, the application of the infection control current is restricted to the refractory periods of portions, e.g., the atria and/or ventricles, of the cardiac muscle (i.e., the heart). Since the heart cannot be stimulated during these time periods, the heart's operation is not affected by this infection control current. In a next operational mode, the infection control current is applied at a frequency that is too high to stimulate the heart.
Thus, a primary feature, of the present invention is the use of electric currents to control/treat infections associated with a cardiac stimulation device without adversely effecting the operation of the cardiac stimulation device or the heart.
Another feature of the present invention is the use of the casing (housing) of the device as one of its electrodes for supplying (or sinking) the electrical current.
In a first treatment mode, the present invention is used, preferably in conjunction with a course of antibiotics, when an infection is first detected.
In a second treatment mode, the present invention can be used prophylactically following implantation of the cardiac stimulation device in conjunction with the traditionally applied antibiotic treatment that follows surgery.
Other and further features, advantages, and benefits of the invention will become apparent in the following description taken in conjunction with the following drawings. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings which are incorporated in and constitute a part of this invention, illustrate one of the embodiments of the invention, and together with the description, serve to explain the principles of the invention in general terms. Like numerals refer to like parts throughout the disclosure.
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Costerton, J.W. et al,Practical Measures to Control Device-Related Bacterial Infections, The Interaction Journal of Artificial Organs, vol. 16, No. 11, pp. 765-770 (1993).
Costerton, J.W. et al,Mechanism of Electrical Enhancement of Efficacy of Antibiotics in Killing Biofilm Bacteria, Antimicrobial Agents and Chemotherapy, vol. 38, No. 12, pp. 2803-2809 (Dec. 1994).
Jass, J. et al,The Effect of Electrical Currents and Tobramycin on
Adinolfi David W.
Kroll Mark W.
Mandell Lee J.
Evanisko George R.
Pacesetter Inc.
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