Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2000-06-27
2001-06-26
Kamm, William E. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06253108
ABSTRACT:
FIELD OF OUR INVENTION
Our invention is directed towards a method for treating cardiac dysfunction arising from post-defibrillation electromechanical dissociation, and to an apparatus for providing such treatment. In particular, the invention relates to an implantable cardiac cardioverter-defibrillator, capable of detecting fibrillation, delivering a defibrillating shock, sensing electrical cardiac rhythmicity coupled with inadequate blood flow and delivering a therapy to restore cardiac function.
BACKGROUND OF OUR INVENTION
Electromechanical dissociation (EMD) is a clinical condition of cardiac arrest with no palpable pulse or blood flow although coordinated ventricular electrical activity exists. This does not exclude the possibility of very weak ventricular contractions, not usually perceptible by standard external or indirect clinical means, which do not produce significant perfusion pressure capable of sustaining life. EMD may occur as the primary modality of cardiac arrest, distinct from fibrillation. Where EMD occurs, the prognosis for recovery is very poor, with survival rates reported on the order of a few percent. When persistent and untreated, EMD is associated with global ischaemia, which will result in rapidly progressive and irreversible brain damage within minutes.
EMD also commonly occurs after defibrillation. In the past, the accepted remedy has been to provide continued life-support while waiting for cardiac output to return. Life support measures commonly include CPR and the administration of drugs such as epinephrine in connection with a search for and removal of reversible causes for the condition. Chest compressions and ventilation may extend the period of viability, although it is well known that standard CPR is a poor substitute for cardiac contractions. If cardiac output does not spontaneously return death is probable. This may particularly be the case for patients with implantable automatic cardioverter-defibrillators. The device may terminate an episode of ventricular fibrillation, cardiac electrical rhythm may be restored, and the patient may nevertheless die as a result of EMD.
The basic implantable cardioverter/defibrillator system consists of at least one electrode attached to the heart and connected by a flexible lead to a shock or pulse generator. This generator is a combination of a power source and the microelectronics required for the system to perform its intended function. An implantable cardioverter/defibrillator may also include a pacemaker to treat bradycardia. Many cardioverter/defibrillators in current use incorporate circuits and antennae to communicate non-invasively with external instruments called programmers. Implantable cardioverters/defibrillators have the capability of correcting dangerous tachyarrhythmias and fibrillation by applying selected stimulation patterns or high-energy shocks. High-energy shocks are used primarily to correct life-threatening tachyarrhythmias by essentially stopping the heart and allowing an appropriate rhythm to re-establish itself.
There remains a need, however, for apparatus that can not only terminate fibrillation, but can also identify post-defibrillation electromechanical dissociation, and provide a therapy.
It is an object of our invention, therefore, to provide a method for treating post-defibrillation electromechanical dissociation.
It is also an important object of our invention to provide an apparatus that can stimulate the heart in the presence of post-defibrillation EMD in such a manner as to restore life-sustaining cardiac output.
Another important object of our invention is to provide an implantable cardioverter-defibrillator with apparatus for sensing and treating post-defibrillation EMD.
SUMMARY OF OUR INVENTION
We have invented an implantable defibrillator, which may include cardioversion and pace maker capabilities, which has the capability of detecting and treating post defibrillation EMD. The implantable defibrillator of our invention comprises a power source and microelectronic apparatus in a hermetically sealed case, and means for detecting and treating EMD.
The stimulator/defibrillator may be connected to the heart by one or more leads, the leads bearing electrodes. At least one electrode serves as an indifferent electrode, which electrode may be part of the hermetically sealed case. At least one electrode for defibrillation is also provided. This electrode may be an endocardial or epicardial electrode or other suitable defibrillation electrode, as is known in the art. A sense circuit senses the electrical condition of the heart of the patient. A hemodynamic sensor is also provided for sensing a parameter correlated to the state of blood flow. The cardiac stimulator/defibrillator is capable of detecting ventricular tachyarrhythmia including fibrillation and providing a therapy to terminate ventricular tachyarrhythmia. After termination of the ventricular tachyarrhythmia, the stimulator/defibrillator can detect the presence of electrical rhythm in the heart correlated, however, with inadequate blood flow to sustain life (i.e., EMD). Under such conditions, the device provides an output to stimulate the heart to overcome electromechanical dissociation and restore adequate blood flow.
The device of our invention may also be used as an external therapy device, as part of, or in conjunction with an external defibrillator. We have also invented a method for treating the heart to restore blood flow where electromechanical dissociation occurs after termination of a ventricular tacyarrhythmia or ventricular fibrillation. The method comprises identifying electromechanical dissociation after termination of a ventricular tach arrhythmia or a fibrillation and providing electrical therapy, the therapy comprising a series of packets of electrical pulses.
We will now describe our preferred embodiment of our invention, in connection with the accompanying drawings.
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Deno D. Curtis
Rosborough John P.
Intermedics Inc.
Kamm William E.
Schwegman Lundberg Woessner & Kluth P.A.
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