Surgery – Instruments – Electrical application
Reexamination Certificate
2001-08-31
2004-05-25
Gibson, Roy D. (Department: 3739)
Surgery
Instruments
Electrical application
C606S041000
Reexamination Certificate
active
06740080
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to an electrophysiological (“EP”) system for providing radio frequency (“RF”) energy to biological tissue and, more particularly, to an ablation system having multiple selectable current path means for directing the flow of current through tissue in energy and time efficient manners.
2. Description of Related Art
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.
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 typically placed on the back 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, electrodes carried by an EP catheter 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. When the blood temperature reaches approximately 100° C., coagulum can occur. Blood coagulation is a major limitation or complication associated with RF ablation therapy. Coagulation can lead to thromboembolism and also form an insulating layer around the electrode, thereby hindering further energy delivery required for ablation therapy. Thus, heating of blood is a major concern for ablation safety and efficacy.
A basic configuration of an RF ablation system, as shown in
FIG. 1
, includes an ablation catheter and a backplate. The ablation catheter includes a distal tip which is fitted with a tip electrode for applying RF energy. The tip electrode is the source of an electrical signal that causes heating of the contacting and neighboring tissue. The tip electrode act as one electrical pole. The other electrical pole is provided by the backplate which is in contact with a patient's external body part. The backplate acts as a current path means in that it establishes a current path with respect to the tip electrode. During operation, a RF signal, typically in the 500 kHz region, is applied to the tip electrode. The current path for the RF signal established between the tip electrode and the backplate produces a localized RF heating effect in the tissue which in turn produces a lesion. In order to obtain a deep, localized lesion at the contacting tissue, i.e., target tissue, using a given amount of RF energy, the backplate and tip electrode should be optimally positioned relative each other, not as shown in
FIG. 1
, such that the target tissue is located between the tip electrode and the backplate. However, the backplate may not always be located in the optimal position. Specifically, if the backplate is positioned such that the target tissue is not between the ablating tip electrode and the backplate, as shown in
FIG. 1
, the current that enters the tissue conducts away from the tissue interior toward the backplate, causing more energy to be dissipated into the blood. The net result of the redistribution of current is a measurable difference in lesion depth and size. In order to obtain a lesion of quality similar to that obtainable when the backplate is in the optimal position, the amount of current flowing through the tissue must be increased. However, this presents a risk that the blood may be heated to the point where coagulum forms (100° C.) before achieving a desired lesion volume. Alternatively, the backplate may be physically repositioned on the patient in order to place it in the optimal position. This is undesirable for the patient because it increases the overall time of the procedure.
Hence, those skilled in the art have recognized a need for an ablation system having multiple and selectable current path means for directing a current through target tissue to thereby create a quality lesion in a safe and efficient manner. The invention fulfills these needs and others.
SUMMARY OF THE INVENTION
Briefly, and in general terms, the invention is directed to a system and method for selectively providing RF energy to biological tissue and, more particularly, to an ablation system having multiple selectable current path means for directing the flow of current through tissue in energy and time efficient manners.
In one aspect, the invention relates to a system for delivering energy to any one of a plurality of tissue regions at a biological site within a biological body. The system includes at least one primary electrode that is adapted to be positioned adjacent any one of the plurality of tissue regions. Also included in the system is a plurality of secondary electrodes adapted to be positioned about the biological site such that any one of the plurality of tissue regions is interposed between at least one of the secondary electrodes and the at least one primary electrode. The system also includes a power generator that is adapted to provide power to the at least one primary electrode. Further included is a switching device that is adapted to selectively couple one
Jain Mudit K.
KenKnight Bruce
Morris Milton M.
Cardiac Pacemakers Inc.
Fulwider Patton Lee & Utecht LLP
Gibson Roy D.
Roane Aaron
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