Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2000-08-07
2002-09-24
Bockelman, Mark (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06456877
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a discharge circuit for use in a multielectrode defibrillator or cardioverting device and methods of using such a circuit.
2. Background
Cardiac devices for treating electrical malfunctions of a heart are known. These devices operate by delivering an electrical shock to the heart, which typically stimulates the heart and causes it to begin beating normally. Various devices have been developed over the years for treating a variety of different malfunctions. Some such devices are designed to monitor the heart and deliver a therapeutic shock automatically upon detection of a malfunction. Other devices operate manually, delivering a shock only upon intervention by a user.
One cardiac device is a defibrillator. A defibrillator delivers a relatively large electric shock to a heart that is in fibrillation. Early defibrillators delivered a monophasic shock to the heart. In a monophasic shock, the polarity of the voltage remains the same throughout the shock. It was soon discovered, however, that a biphasic shock can be more effective in treating fibrillation than a monophasic shock. In a biphasic shock, a first portion of the waveform applied to the heart has a first polarity and a second portion of the waveform has an opposite polarity. Typically, a biphasic shock is able to defibrillate a heart with less energy and/or voltage than a monophasic shock.
Known circuits for delivering a biphasic shock utilize either a single discharge capacitor or two discharge capacitors configured to act as a single capacitor. An example of the former circuit is shown in FIG.
1
. As shown in
FIG. 1
, four switches
104
,
106
,
114
, and
116
control the discharge of capacitor
102
through electrodes
108
and
112
into heart
110
. Upon determination that a defibrillating shock needs to be delivered to heart
110
, a charging circuit (not shown) charges capacitor
102
. When capacitor
102
is sufficiently charged, switches
104
and
116
are closed, while switches
106
and
114
remain open. Capacitor
102
begins to discharge, creating a current that flows from electrode
108
to electrode
112
. When capacitor
102
has only partially discharged, switches
104
and
116
are opened. Shortly thereafter, switches
106
and
114
are closed. Capacitor
102
then continues to discharge, but this time current flows from electrode
112
to electrode
108
. The circuit shown in
FIG. 1
is commonly referred to as an “H” bridge.
FIG. 2
illustrates an example of a prior art circuit in which two capacitors arranged to act as a single capacitor create a biphasic shock. In the circuit of
FIG. 2
, four switches
206
,
208
,
216
, and
218
control discharge of two capacitors
202
and
204
through electrodes
210
and
214
into heart
212
. As with the circuit of
FIG. 1
, a charging circuit (not shown) charges capacitors
202
and
204
. When these capacitors are sufficiently charged, switches
206
and
218
are closed, while switches
208
and
216
remain open. Capacitors
202
and
204
, in series, begin to discharge, creating a current that flows from electrode
210
to electrode
214
. When these capacitors have only partially discharged, switches
206
and
218
are opened. Shortly thereafter, switches
208
and
216
are closed. With switches
208
and
216
closed and switches
206
and
218
open, capacitor
204
—but not capacitor
202
—is charges. This creates a current that flows from electrode
214
to electrode
210
.
The timing of the opening and the closing of the switches in
FIGS. 1 and 2
is typically controlled using one of three general methods. The first is known as the fixed tilt method. Switches
104
and
116
or switches
206
and
218
are closed until the voltage on capacitor
102
or capacitors
202
and
204
falls below a predetermined level. Once the voltage on these capacitors falls to the predetermined level, switches
104
and
116
or switches
206
and
218
are opened. The second general method of controlling the switches is known as the fixed duration method. Switches
104
and
116
or switches
206
and
218
are closed for a predetermined period of time. Once the predetermined period of time expires, the switches are opened. The third general method of controlling the timing of the opening and closing of the switches is a hybrid of the fixed tilt method and the fixed duration method. Switches
104
and
116
or switches
206
and
218
are closed for a predetermined period of time that begins when the voltage on capacitor
102
or capacitors
202
and
204
falls below a predetermined level.
Because of the high voltages and currents required to defibrillate a heart, the switches in circuits such as those shown in
FIGS. 1 and 2
must be rugged. In particular, they must be capable of “hot switching”, i.e., closing and opening when there is a high voltage potential across the switch. Examples of switches that have been used in prior art devices include, but are not limited to, metal oxide semiconductor field effect transistors, insulated gate field effect transistors, insulated gate bipolar transistors, and silicon controlled rectifiers.
SUMMARY OF THE INVENTION
The present invention is directed to a discharge circuit for use in a multielectrode defibrillator or cardioverting device and methods of using such a circuit. The circuit includes at least two electrodes that are in electrical contact with a heart. Upon determination that a therapeutic shock needs to be applied to the heart, two capacitors configured for independent discharge are charged. Once these capacitors are sufficiently charged, one of the capacitors is switched such that it begins to discharge into the heart. At an appropriate time, this capacitor is switched again such that it no longer discharges into the heart. At this time, the other capacitor is switched such that it begins to discharge into the heart, and at the appropriate time, it is switched such that it stops discharging into the heart. The two capacitors are preferably configured with opposite polarities so that the waveform applied to the heart by the sequential discharging of the two capacitors is biphasic.
REFERENCES:
patent: 4953551 (1990-09-01), Mehra et al.
patent: 5199429 (1993-04-01), Kroll et al.
patent: 5948004 (1999-09-01), Weijand et al.
patent: 5968080 (1999-10-01), Brewer et al.
patent: 6047211 (2000-04-01), Swanson et al.
patent: 6263239 (2001-07-01), Brewer et al.
patent: 6411846 (2002-06-01), Brewer et al.
Bockelman Mark
Mitchell Steven M.
Pacesetter Inc.
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