Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-06-28
2001-08-28
Kamm, William E. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06280461
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the treatment of heart defects by the administration of electrical therapy. More particularly, this invention relates to an energy-delivery apparatus for imparting the electrical therapy to the heart.
2. Description of the Related Art
Technology is available for correcting excessively slow heart rates (bradycardia) using implantable devices, commonly referred to as pacemakers, which deliver microjoule electrical pulses to a slowly beating heart in order to speed the heart rate up to an acceptable level. Also, it is well known to deliver high energy shocks (e.g., 180 to 360 joules) via external paddles applied to the chest wall in order to correct excessively fast heart rates, and prevent the possible fatal outcome of ventricular fibrillation or certain ventricular tachycardias. Bradycardia, ventricular fibrillation, and ventricular tachycardia are all electrical malfunctions (arrhythmias) of the heart. Each may lead to death within minutes unless corrected by the appropriate electrical stimulation.
One of the most deadly forms of heart arrhythmias is ventricular fibrillation, which occurs when the normal, regular electrical impulses are replaced by irregular and rapid impulses, causing the heart muscle to stop normal contractions and to begin to quiver. Normal blood flow ceases, and organ damage or death may result in minutes if normal heart contractions are not restored. Although frequently not noticeable to the victim, ventricular fibrillation is often preceded by ventricular tachycardia, which is a regular but fast rhythm of the heart. Because the victim has no noticeable warning of the impending fibrillation, death often occurs before the necessary medical assistance can arrive.
Because time delays in applying the corrective electrical treatment may result in death, implantable pacemakers and defibrillators have significantly improved the ability to treat these otherwise life threatening conditions. Being implanted within the patient, the device continuously monitors the patient's heart for treatable arrhythmias and when such is detected, the device applies corrective electrical pulses directly to the heart.
Normal heart function often can be restored to a person suffering ventricular fibrillation or ventricular tachycardia by a procedure known as cardioversion, the synchronized application of electric therapy to the heart muscle. Pacemakers and defibrillators that apply corrective electrical pulses externally to the patient's chest wall also are used to correct such lifethreatening arrhythmias but suffer from a drawback insofar as it may not be possible to apply the device in time during an acute arrhythmic emergency to save the patient's life. Such treatment is needed within a few minutes to be effective.
Consequently, when a patient is deemed at high risk of death from such arrhythmias, electrical devices often are implanted so as to be readily available when treatment is needed. Alternatively, such patients are kept in a hospital where corrective electrical therapy is generally close at hand. Long term hospitalization, however, is frequently impractical due to its high cost, or due to the need for patients to engage in normal daily activities.
There also are many patients susceptible to heart arrhythmias who are at temporary risk of sudden death. For example, patients who have suffered a myocardial infarction are at substantial risk of tachyarrhythmias for several weeks thereafter. Such patients generally are hospitalized but could be discharged earlier if there were a practical means to protect them from life threatening arrhythmias. Additionally, patients awaiting implantation of an automatic defibrillator may require an external defibrillator to be close at hand, in case they experience a life-threatening tachyarrhythmia. Furthermore, some patients who may benefit from an implantable defibrillator may face an inordinate risk from the surgery required for implanting such a device.
It is evident from the above that there is a need for providing an effective means whereby susceptible patients can receive timely defibrillation or cardioversion without having to undergo an implant procedure and without having to remain hospitalized. Such a device should be capable of determining the energy as it is being delivered to the patient in order to monitor effective treatment, as well as determine that the device is in proper operating condition for delivering these therapeutic energy pulses to the patient.
SUMMARY OF THE INVENTION
The present invention provides for a patient-worn energy delivery apparatus for imparting electrical therapy to the body of a patient responsive to an occurrence of a treatable condition. The apparatus includes a voltage converter for converting electrical energy from an initial voltage to a final voltage. Preferably, the energy is converted at a plurality of charging rates.
The energy delivery apparatus in accordance with the present invention also includes a defibrillator electrically coupled between the converter and the patient and the defibrillator has an energy reservoir for receiving the electrical energy. The defibrillator produces preshaped electrical pulses such as defibrillation pulses and cardioversion pulses. The defibrillator preferably includes at least one insulated gate bipolar transistor for applying the electrical energy to the patient.
The apparatus additionally includes an energy delivery controller electrically coupled to the patient and the converter and the defibrillator. The controller causes the converter to provide the electrical energy to the defibrillator at a specific charging rate in response to an energy level in the reservoir. The plurality of charging rates correspond with a plurality of duty cycles which correspond to a selected output voltage level.
The controller causes the defibrillator to apply a selectable portion of the electrical energy in the form of electrical pulses to the body of the patient in response to the occurrence of the treatable condition. Preferably, the preshaped electrical pulses are approximately exponentially-shaped pulses and may be monophasic or biphasic exponential pulses. The selectable portion is preferably determined by the controller using a minimum energy delivery period and a maximum energy delivery period. The controller measures the voltage and current being delivered to the patient during the pulse delivery period to measure the actual amount of energy being delivered to the patient.
The apparatus further provides means for measuring the electrical energy as it is being delivered to the body of the patient through a plurality of electrodes interposed between the defibrillator and the patient. The apparatus periodically measures the voltage and current of the pulse being delivered. In a preferred embodiment, these measurements are rapidly periodically taken, on the order of every 94 microseconds, and stored for later analysis. The pulse is terminated when the desired energy level has been delivered to the patient. In the event of a malfunction, such as an overvoltage condition sensed by the apparatus, the pulse can be truncated so as to prevent harm to the patient or damage to the apparatus.
In a preferred embodiment, a programmable logic device receives the measured pulse voltage and the measured pulse current as inputs and calculates the energy level as it is delivered to the patient over time. If the energy level is equal to or exceeds a predetermined maximum energy level, the pulse is truncated.
The defibrillator may further include a plurality of silicon controller rectifiers and opto-triacs and selected ones of the capacitors may be serially connected with other capacitors and respective ones of the silicon controlled rectifiers may be serially interposed between adjacent capacitors. Each of the silicon controlled rectifiers may be controllable with the opto-triacs which cause the silicon controlled rectifiers to conduct responsive to a therapy initiation command from the
Glegyak John A.
Kaib Thomas E.
Peduzzi David J.
Russial Joseph
Buchanan Ingersoll P.C.
Kamm William E.
Lifecor, Inc.
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