Implantable medical stimulation apparatus with intra-conductor capacitive energy storage

An implantable device electrically stimulates an organ of an animal in response to a trigger event. Between trigger event that device receives a wireless signal, such as a radio frequency signal, and stores energy from the signal in a plurality of capacitors. The capacitors are located within a electrical lead that extends to a stimulation electrode attached to the organ. That electrical lead has a hollow outer insulating tube with a pair of conductors extending longitudinally therein. The plurality of capacitors are connected between the pair of conductors. Thus the electrical lead serves as both a conductor of a stimulation current to the electrode and a housing for the plurality of capacitors.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to implantable medical devices which produce electrical pulses that to stimulate organs of an animal, and more particularly to the storage of energy in such medical devices.

2. Description of the Related Art

A remedy for people with slowed or disrupted natural heart activity involves implanting a cardiac pacing device which is a small electronic apparatus that stimulates the heart to beat at regular rates.

Typically the pacing device is implanted in the patient's chest and has sensor electrodes that detect electrical impulses associated with in the heart contractions. These sensed impulses are analyzed to determine when abnormal cardiac activity occurs, in which event a pulse generator is triggered to produce electrical pulses. Wires carry these pulses to electrodes placed adjacent specific cardiac muscles, which when electrically stimulated contract the heart chambers. It is important that the stimulation electrodes be properly located to produce contraction of the heart chambers.

Modern cardiac pacing devices vary the stimulation to adapt the heart rate to the patient's level of activity, thereby mimicking the heart's natural action. The pulse generator modifies that rate by tracking the activity of the sinus node of the heart or by responding to other sensor signals that indicate body motion or respiration rate.

U.S. Pat. No. 6,445,953 describes a cardiac pacemaker that has a pacing device, which can be located outside the patient, to detect abnormal electrical cardiac activity. In that event, the pacing device emits a radio frequency signal, that is received by a stimulator implanted in a vein or artery of the patient's heart. Specifically, the radio frequency signal induces a voltage pulse in an antenna on the stimulator and that pulse is applied across a pair of electrodes, thereby stimulating adjacent muscles and contracting the heart.

Although this cardiac pacing apparatus offered several advantages over conventional pacemakers, it required that sufficient energy be derived from the received radio frequency signal to power the implanted circuit and to stimulate the adjacent organ. The amount of energy required may be relatively great, especially when the apparatus is an implantable defibrillator.

Therefore, it is desirable to provide an energy storage mechanism in the implanted apparatus which will accumulate energy from a radio frequency signal and provide that accumulated energy when needed for organ stimulation.

SUMMARY OF THE INVENTION

An apparatus is provided to artificially stimulate an organ of an animal. That apparatus includes a first electrode and a second electrode for implantation into the animal. An electrical lead has a first conductor and a second conductor with a plurality of capacitors connected to the first and second conductors. The plurality of capacitors may be connected in parallel or in series between the first and second conductors.

An element is provided for receiving wireless signals, which may be in the radio frequency spectrum, for example. A stimulation circuit is connected to the first electrode, the first conductor, the second conductor and the element. The stimulation circuit uses energy from a received first wireless signal to charge the plurality of capacitors with electrical energy. In response to a trigger event, the stimulation circuit applies the electrical energy from plurality of capacitors to the first and second electrodes to electrically stimulate the organ of the animal.

The trigger event may be the receipt of a second wireless signal that has a unique format which indicates that stimulation should occur. In this case, the second wireless signal may emanate from a pacing circuit that detects when artificial pacing of a heart if required. In another case, the wireless signal may emanate from a circuit that detects when cardiac defibrillation is required.

DETAILED DESCRIPTION OF THE INVENTION

With initial reference toFIG. 1, a pacing apparatus10electrically stimulates a medical patient's heart12to contract or to convert from fibrillation to a normal rhythm. That apparatus comprises an external pacing device14and a stimulator20that is implanted in a blood vessel18of a muscle in the heart. As will be described in greater detail, the pacing device14transmits a radio frequency signal16which causes the stimulator20to emit an electric current that stimulates the heart muscle.

Referring toFIG. 2, the pacing device14, that preferably is worn outside the patient's body adjacent the chest, comprises a conventional pacing signal generator22connected to input electrodes23attached to the patient's body. Alternatively, the pacing device14may be implanted in the patient. The internal circuitry and operation of the pacing signal generator22are similar to prior cardiac pacers. However, instead of the output stimulation signals being applied to the electrodes via leads, the pacing signals are applied to an input of a radio frequency (RF) transmitter24. In response to the stimulation signal (also known as a pacing signal) from the generator22, the radio frequency transmitter24generates a pulse of the radio frequency signal16that is transmitted throughout the chest cavity via an antenna26. Preferably the antenna26either is located relatively close to the heart12or is of a type which focuses the radio frequency signal toward the heart. Both the pacing signal generator22and the RF transmitter24are powered by a battery28.

As illustrated inFIG. 3, the stimulator20is placed in an artery or vein18in close proximity to the atria or ventricles of the heart12. For example the vascular stimulator20may be positioned in the coronary sinus vein. The stimulator20includes a body30similar to well-known expandable vascular stents that are employed to enlarge a restricted vein or artery. The body30has a generally tubular shape that initially is collapsed to a relatively small diameter enabling the stimulator to pass freely through blood vessels of a patient. The procedure for implanting the stimulator20is similar to that used for vascular stents. For example, a balloon at the end of a standard catheter is inserted into the stimulator20in a collapsed configuration. That assembly is inserted through an incision in a vein or artery near the skin of a patient and passed through the vascular system to the appropriate location proximate to the atria or ventricles of the heart12. The balloon of the catheter then is inflated to expand the stimulator20, thereby slightly enlarging the blood vessel18which embeds the stimulator in the wall of the vein or artery. The balloon is deflated, the catheter is removed from the patient, and the incision is closed. Alternatively, a self-expanding body30may be utilized. The slight enlargement of the blood vessel18and the tubular design of the body30allows blood to flow relatively unimpeded through the vascular stimulator20.

With additional reference toFIG. 4, the stimulator20has a stimulation circuit32and a receive antenna34in the form of a wire coil wound circumferentially around the body30. A first electrode36in the form of a ring encircles the body. The stimulation circuit32includes an RF signal detector38having an input connected to the receive antenna34and tuned to the frequency of the RF signal16that is emitted by the pacing device14. The RF signal detector38converts the energy of that RF signal into an electric voltage that charges a storage capacitor40which supplies electrical power to the circuitry on the vascular stimulator20. The periodic pulses of the RF signal charge the storage capacitor40so that it will have sufficient stored energy when stimulation of the heart is required.

A first electrode36in the form of a ring encircles the body is connected to one terminal of the storage capacitor40. A second electrode44is adjacent to the wall of a blood vessel46in another section of the heart, as seen inFIG. 3, and is coupled to the stimulation circuit32by an insulated electrical lead48extending through the blood vessels. The relatively small size of the second electrode44allows it to be placed into a significantly smaller blood vessel46than the vascular stimulator20. As a result, the second electrode44can be placed is a greater variety of locations in the cardiac vascular system and in close proximity to the muscles that contract the desired portion of the heart12.

In order to provide a enough electrical energy for stimulation, especially for defibrillation, as relatively large storage capacitance is required. Instead of placing that capacitance on the body30of the stimulator20, a plurality of capacitors are placed along the length of the electrical lead48that connects the second electrode44to the stimulation circuit32. With reference toFIG. 5, the electrical lead48has a tubular shell50of insulated material with two conductors51and52extending longitudinally along the central opening. A plurality of disk-shaped capacitors54also are spaced along that central opening. These capacitors54may be conventional surface mount type devices, such as model PCC2232CT which is 4.7 μf, 16 WVDC capacitor available from Panasonic Corporation of North America in Secaucus, N.J. 07094. The terminal on one side of each capacitor54is connected to the first electrical conductor51and the other terminal is connected to the second conductor52. Therefore, the plurality of capacitors54are connected in parallel so that the individual capacitances are summed to form a large equivalent storage capacitor40.

FIG. 6illustrates an alternative structure for the electrical lead48which has an tubular insulated shell60with first and second conductors61and62extending longitudinally along the central opening. A plurality of disk-shaped capacitors64are connected in series between the first and second conductors61and62, in contrast with electrical lead48in which the capacitors54are connected in parallel.

Referring again toFIG. 4, the pacing device14periodically transmits the radio frequency signal16to the stimulator20. The RF signal detector38derives electrical voltage from the energy of that RF signal and applies that voltage across conductors51and52to charge the plurality of capacitors64that form the storage capacitor40. Thus a sufficient charge is maintained on the storage capacitor40for when cardiac stimulation is needed.

The pacing device14also responds to the electrical signals from the heart, that are detected by the input electrodes23, by determining in a conventional manner when cardiac stimulation is to required. When stimulation is to occur, the RF transmitter sends a uniquely shaped RF signal pulse sequence. The RF signal detector38inFIG. 4responds to that RF signal pulse sequence by activating a pulse circuit42that closes a switch45connected to a second electrode. That action completes a circuit thereby dumping the voltage stored on the capacitor across the first and second electrodes36and44which stimulates the heart tissue between those electrodes.

FIG. 7illustrates a third structure for the electrical lead48which has an tubular insulated shell70with first and second conductors71and72extending longitudinally along the central opening. A plurality of disk-shaped capacitors74-80are located within central opening. The capacitors are connected in groups with the devices in each group being coupled in series with the groups connected in parallel to the first and second conductors71and72. Specifically, one group comprises capacitors74,75and76that are connected in series with the first capacitor74in that group having a terminal that is coupled to the first conductor71and the last capacitor76in that group having a terminal that is coupled to the second conductor72. Another group comprises capacitors77,78and79connected in series with the first capacitor74coupled to the first conductor71and the last capacitor76coupled to the second conductor72. The number of capacitors in each group and the number of groups are chosen to provide the desired cumulative capacitance and working voltage for the storage capacitor40of the stimulator20.

The foregoing description was primarily directed to preferred embodiments of the invention. Even though some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.