Surgery – Instruments – Electrical application
Reexamination Certificate
1999-06-17
2002-05-21
Dvorak, Linda C. M. (Department: 3739)
Surgery
Instruments
Electrical application
C606S039000, C606S040000, C606S041000, C606S042000, C606S046000, C606S049000, C607S113000, C607S115000
Reexamination Certificate
active
06391024
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to an electrophysiological (“EP”) apparatus and method for providing energy to biological tissue, and more particularly, to an EP apparatus and method for assessing the adequacy of contact between an ablation electrode and biological tissue. The invention also relates to an apparatus and method for providing energy to biological tissue while simultaneously monitoring the electrical activity within the tissue.
The heart beat in a healthy human is controlled by the sinoatrial node (“S-A node”) located in the wall of the right atrium. The S-A node generates electrical signal potentials that are transmitted through pathways of conductive heart tissue in the atrium to the atrioventricular node (“A-V node”) which in turn transmits the electrical signals throughout the ventricle by means of the His and Purkinje conductive tissues. Improper growth of, or damage to, the conductive tissue in the heart can interfere with the passage of regular electrical signals from the S-A and A-V nodes. Electrical signal irregularities resulting from such interference can disturb the normal rhythm of the heart and cause an abnormal rhythmic condition referred to as “cardiac arrhythmia.”
While there are different treatments for cardiac arrhythmia, including the application of anti-arrhythmia drugs, in many cases ablation of the damaged tissue can restore the correct operation of the heart. Such ablation can be performed by percutaneous ablation, a procedure in which a catheter is percutaneously introduced into the patient and directed through an artery to the atrium or ventricle of the heart to perform single or multiple diagnostic, therapeutic, and/or surgical procedures. In such case, an ablation procedure is used to destroy the tissue causing the arrhythmia in an attempt to remove the electrical signal irregularities or create a conductive tissue block to restore normal heart beat or at least an improved heart beat. Successful ablation of the conductive tissue at the arrhythmia initiation site usually terminates the arrhythmia or at least moderates the heart rhythm to acceptable levels. A widely accepted treatment for arrhythmia involves the application of RF energy to the conductive tissue.
In the case of atrial fibrillation (“AF”), a procedure published by Cox et al. and known as the “Maze procedure” involves continuous atrial incisions to prevent atrial reentry and to allow sinus impulses to activate the entire myocardium. While this procedure has been found to be successful, it involves an intensely invasive approach. It is more desirable to accomplish the same result as the Maze procedure by use of a less invasive approach, such as through the use of an appropriate EP catheter system providing RF ablation therapy. In this therapy, transmural ablation lesions are formed in the atria to prevent atrial reentry and to allow sinus impulses to activate the entire myocardium.
There are two general methods of applying RF energy to cardiac tissue, unipolar and bipolar. In the unipolar method a large surface area electrode; e.g., a backplate, is placed on the chest, back or other external location of the patient to serve as a return. The backplate completes an electrical circuit with one or more electrodes that are introduced into the heart, usually via a catheter, and placed in intimate contact with the aberrant conductive tissue. In the bipolar method, electrodes introduced into the heart have different potentials and complete an electrical circuit between themselves. In the bipolar method, the flux traveling between the two electrodes of the catheter enters the tissue to cause ablation.
During ablation, the electrodes are placed in intimate contact with the target endocardial tissue. RF energy is applied to the electrodes to raise the temperature of the target tissue to a non-viable state. In general, the temperature boundary between viable and non-viable tissue is approximately 48° Centigrade. Tissue heated to a temperature above 48° C. becomes non-viable and defines the ablation volume. The objective is to elevate the tissue temperature, which is generally at 37° C., fairly uniformly to an ablation temperature above 48° C., while keeping both the temperature at the tissue surface and the temperature of the electrode below 100° C.
In order to produce effective transmural lesions it is necessary to ensure that the electrodes are in intimate contact with the tissue. Positioning of the electrodes is typically done visually under fluoroscopy imaging and is thus largely a function of a physician's training and experience. Assessment of adequate electrode/tissue contact is somewhat of an art and verification, at present, is typically inferred through comparison of pre- and post-ablation electrocardiogram (“ECG”) analysis.
The use of impedance as an indication of electrode/tissue contact has been reported in the treatment of focal arrhythmias, such as ventricular tachyarrhythmia. In these procedures, a catheter with a single combination ablation/impedance-measuring tip electrode is inserted into the local blood pool within the heart and an impedance measurement is taken. The tip electrode is then placed at an ablation location and, so as to push the tip electrode deep into the cardiac tissue, force is applied along the axis of the catheter. An impedance measurement is then taken and compared to the impedance of the blood pool. This subsequent impedance measurement is referred to as a “contact-assessment” impedance. A significant increase in the contact-assessment impedance relative the blood-pool impedance serves as an indication that the tip electrode is in contact with cardiac tissue.
In this procedure a significant increase in impedance is noted due to the fact that the tip electrode is pushed deep into the cardiac tissue and is thus largely surrounded by tissue, as opposed to blood. While this electrode/tissue contact assessment technique is effective for the treatment of focal arrhythmias, it is less effective for the treatment of non-focal arrhythmias, such as atrial fibrillation. Ablation therapy for atrial fibrillation often involves the formation of transmural linear lesions. In this form of ablation therapy a linear array of band electrodes is placed against the atrial wall. While the band electrodes are held against the tissue with some degree of force, a portion of the band electrodes is likely to remain in the blood pool. The presence of blood against a portion of the band electrode affects the impedance measurement and reduces the significance of the difference between the blood-pool impedance and the contact-assessment impedance. Thus, the above-described electrode/tissue contact assessment technique that relies on the use of a tip electrode forced into the tissue is ineffective for linear ablation therapy. This known technique is further ineffective for linear ablation because it does not account for fluctuations in impedance measurements which may occur due to movement of electrodes caused by respiration and heart contractions.
As previously mentioned, in present ablation procedures, once ablation therapy is completed, the effectiveness of the therapy is verified through electrocardiogram (“ECG”) analysis. Ablation therapy is completed upon the application of ablation energy for a prespecified time period. Once ablation therapy is completed, the ablation electrode is disconnected from the ablation energy source and is reconnected to an ECG amplifier/recorder. The ECG amplifier/recorder collects electrical data from the heart through the ablation electrode. The ECG amplifier/recorder analyzes the electrical data and produces signals indicative of the electrical activity through the heart tissue and particularly the ablated tissue. This present technique of assessing the effectiveness of ablation is inconvenient in that it requires ablation therapy be completed prior to assessing the ablation results and further requires physical switching from the ablation source to the ECG amplifier/recorder.
Hence, those skilled in the art h
Anderson Russ E.
Bowe Wade A.
Castellano Thomas M.
Lockwood Kathryn E.
Sherman Marshall L.
Cardiac Pacemakers Inc.
Dvorak Linda C. M.
Fulwider Patton Lee & Utecht LLP
Kearney R.
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