Surgery – Diagnostic testing – Structure of body-contacting electrode or electrode inserted...
Reexamination Certificate
2000-06-30
2002-06-04
Dvorak, Linda C. M. (Department: 3739)
Surgery
Diagnostic testing
Structure of body-contacting electrode or electrode inserted...
C600S382000, C600S391000, C600S392000, C600S393000, C607S142000
Reexamination Certificate
active
06400975
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to medical test devices, methods and systems, and more particularly to devices, methods and systems for consistently and accurately measuring and mapping cardiac function, and simultaneously delivering electrical energy to the heart.
BACKGROUND
The heart is composed of a specialized system of cells that generate and conduct electrical impulses; it is these cells which are responsible for propagating muscle contraction, thus facilitating the pumping function of the heart. While over 90 percent of the heart's mass is comprised of muscle fibers, the remaining specialized conduction tissues are distributed throughout the heart in order to enable contraction to be well synchronized. The heart is comprised of 4 chambers: 2 atria and 2 ventricles. Normally cardiac impulses are generated in the sino-atrial (SA) node, located in the right atrium. The signals then pass to the left atrium, and down the bundle of His towards the left and right ventricular bundles. Once arriving at these bundles, the impulse is distributed throughout the ventricles, enabling them to contract, thus pumping blood throughout the pulmonary and systemic circulations. The ventricles are capable of initiating an impulse if the normal SA pathway is disrupted, albeit at a much slower rate. Deviations from the normal pattern often lead to a variety of symptoms, and can predispose the patient to several serious clinical problems including sudden cardiac death (SCD). Problems with the cardiac conduction system are frequently called arrhythmias or dysrhythmias. Dysrhythmias in which the heart beats too slowly often require a pacemaker to raise the rate to more physiologic levels. Ventricular dysrhythmias whereby the heart beats too rapidly, often called tachycardia, can devolve into a life threatening emergency called ventricular fibrillation, which requires defibrillation to treat.
A variety of cardiac disease processes can contribute to the heart beating too slowly to provide appropriate cardiac output. When this occurs, often a pacemaker is required to reestablish proper heart rate. Cardiac pacing, or electrostimulation, involves sending signals from an electrical generator to the heart in order to initiate or sustain a heart rate that is physiologically appropriate. There are a variety of methods to apply such technology, including transthoracic, thransvenous and permanent pacemakers. Transcutaneous pacemakers involve placing electrodes on the skin of the patient, usually one on the chest, and one on the back, in order to deliver high energy impulses. This method is usually reserved for emergency pacing.
In the majority of patients dying suddenly from sudden cardiac death (SCD), primary electrical failure occurs, usually in the form of ventricular fibrillation. Fibrillation is chaotic, asynchronous electrical activity of the heart. The impulse in this dysrhythmia spreads erratically along a variety of changing pathways, instead of originating from a single site, usually the SA node, and then spreading in a highly ordered manner. These fibrillatory impulses result in the different regions of the heart muscle being depolarized randomly in relation to the other areas of the myocardium. Because there is simultaneous relaxation and contraction of the heart muscle cells, depending upon their relation to the fibrillation impulses, there is complete disruption of ventricular contraction, and the loss of pump function. Circulatory collapse ensues, unless rapid and appropriate advanced cardiac life support (ACLS) is initiated.
ACLS involves supplementing basic cardiopulmonary resuscitation with additional interventions, including electrocardiographic monitoring and external pacemaker devices or defibrillation. Successful treatment of patients in ventricular fibrillation depends upon reaching the patient early in the event, and initiating definitive therapy rapidly. Once on the scene, one of the rate limiting steps is the 2 step process of applying electrodes to monitor for the dysrhythmias to define the cardiac mechanism, then applying the defibrillation paddles to deliver the charge to the patient's heart.
Electrical defibrillation is a method used to terminate ventricular fibrillation. It can also be used to terminate atrial and ventricular tachydysrhythmias. The procedure involves placing two paddle electrodes on the chest, and delivering a high-energy shock wave to the heart. If the shock energy is sufficiently powerful, it will depolarize the heart cells, allowing the sinus node to resume initiating cardiac impulses in a more coordinated manner. The objective is to use the lowest amount of energy possible. Unfortunately the large electrode area and skin resistance create the need for larger amounts of energy to be used, which predisposes the patient to discomfort and bums. The energy required to terminate ventricular fibrillation is between 200-400 Joules, depending upon the underlying cardiac pathology, the body habitus of the patient, and the orientation of the heart within the chest cavity. More energy is required to overcome size and resistance. The energy of the electrical discharge can cause myocardial injury.
The process of defibrillation is subject to similar procedural and anatomic problems found in obtaining electrocardiograms (ECG or EKG). The current state of the art involves placing 2 electrodes on the patient's chest. It is well known that fibrillatory signals do not propagate in a coordinated or linear manner simplistically as north to south, left to right. Also, we know resistance to the delivered shock is patient dependent.
It is widely accepted that the success of scientific testing and therapeutic interventional procedures is based upon two criteria: 1. Reproducibility, and 2. Accuracy. Nowhere are these more critically essential than in medicine, especially cardiology, where lives often hang in the balance relying on the results.
The EKG has long been an important diagnostic tool in the field of cardiology. The EKG is used to measure the timing and amplitude of the electrical signal from the subject's heart, presenting the measurements as a visual display. The standard “twelve-lead” EKG involves the separate placement on the patient's body of ten individual electrodes, six precordially and one each on each of the four limbs. The ten electrodes are attached one at a time and must each be placed over a specific point on the patient's body. If any of the precordial electrodes are mixed up with each other, or if the arm or leg electrodes are swapped over, the EKG tracing obtained will be faulty.
The six precordial electrodes are placed on the patient's chest at specific recording zones over the heart. V1 is properly positioned in the fourth intercostal space to the immediate right of the sternum. V2 is also located in the fourth intercostal space, but to the immediate left of the sternum. V4 is positioned in the fifth intercostal space at the midclavicular line. V5 and V6 are similarly located in the fifth intercostal space, but at the anterior axillary and midaxillary lines respectively. Finally, V3 is positioned midway between V2 and V4.
The process of obtaining an EKG tracing is fraught with potential errors. In particular, the technician may make mistakes either in placing the electrodes or in reading the tracing. This is particularly likely in an emergency situation, when the test often must be administered in a hurry and the patient is frequently sweaty, immobile, and minimally cooperative. Further variability and error, in the form of discordant respiratory artifact, is introduced due to the fact that the six precordial electrodes move independently with the patient's respiration, causing noise or spurious signals. Similarly, error is introduced into EKGs performed during stress testing due to the independent motion of the six precordial electrodes, leading to multiple discordant body motion artifact (BMA).
In particular, many studies support the fact that there is a lack of reproducibility in EKG tracings obtai
Banner & Witcoff , Ltd.
Dvorak Linda C. M.
Ruddy David M.
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