Surgery – Instruments – Electrical application
Reexamination Certificate
2001-11-28
2004-02-17
Peffley, Michael (Department: 3739)
Surgery
Instruments
Electrical application
C606S042000
Reexamination Certificate
active
06692492
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to an electrophysiological (“EP”) catheter for providing energy to biological tissue within a biological site and, more particularly, to an EP catheter having a dielectric-coated ablation electrode having a non-coated window with thermal sensors.
2. Description of the Related Art
The heart beat in a healthy human is controlled by the sinoatrial node (“SA node”) located in the wall of the right atrium. The SA node generates electrical signal potentials that are transmitted through pathways of conductive heart tissue in the atrium to the atrioventricular node (“AV node”) which in turn transmits the electrical signals throughout the ventricle by means of the His and Purkinje conductive tissues. Improper growth, remodeling, or damage to, the conductive tissue in the heart can interfere with the passage of regular electrical signals from the SA and AV 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 percutaneously, a procedure in which a catheter is introduced into the patient through an artery or vein and directed 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 to create a conductive tissue block for preventing propagation of the arrhythmia and restoring normal heart function. 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 surgical “Maze procedure” involves the formation of 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. Migration to a percutaneous catheter approach removes the morbidity associated with a surgically opened chest cavity. 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. In this sense transmural is meant to include lesions that pass through the atrial wall or ventricle wall from the interior surface (endocardium) through the cardiac muscle layer (myocardium) to the exterior surface (epicardium).
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 both the unipolar and the bipolar methods, the current traveling between the electrodes of the catheter and between the electrodes and the backplate enters the tissue and induces a temperature rise in the tissue resulting in ablation.
During ablation, RF energy is applied to the electrodes to raise the temperature of the target tissue to a lethal, non-viable state. In general, the lethal temperature boundary between viable and non-viable tissue is between approximately 45° C. to 55° C. and more specifically, approximately 48° C. Tissue heated to a temperature above 48° C. for several seconds becomes permanently non-viable and defines the ablation volume. Tissue adjacent to the electrodes delivering RF energy is heated by resistive heating which is conducted radially outward from the electrode-tissue interface. The goal 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 well below 100° C. In clinical applications, the target temperature is set below 65° C. to minimize coagulum formation. Lesion size has been demonstrated to be proportional to temperature and duration of ablation.
Blood coagulation is a major limitation/complication associated with RF ablation therapy. Coagulation can lead to thromboembolism and can also form an insulating layer around the electrode hindering further energy delivery required for ablation therapy. Heat appears to be a major factor in the formation of blood coagulum on a catheter electrode. During a typical RF energy ablation procedure using an EP catheter, one or more electrodes carried by the catheter are positioned such that a portion of the electrode(s) are in contact with the tissue being ablated while the remaining portion of the electrodes are in contact with blood. The RF energy applied during the procedure resistively heats the tissue which in turn heats the electrode through conduction. As blood stays in contact with the heated electrode, platelet activation and protein binding occur. This platelet activation appears to be a pathway to coagulum formation.
To reduce the possibility of coagulum formation, one or more thermal sensors may be positioned on the electrodes. Temperature readings provided by the sensors are used to monitor the temperature of the electrodes and to automatically control the power delivered to the electrodes in order to maintain the temperature at or below a target temperature. This type of temperature control scheme assumes that the temperature readings provided by the thermal sensors accurately reflect the temperature at the interface between the electrode and the tissue. This may not, however, be the case, particularly when band electrodes are being used or when thermal sensor orientation to the tissue interface is less than optimum.
During an ablation procedure using a band electrode, only a portion of the band electrode contacts the tissue. Depending on the orientation of the band electrode relative to the tissue and the position of the thermal sensor relative to the band electrode, the thermal sensor may not coincide with that portion of the electrode which contacts the tissue. In this situation, the temperature readings provided by the thermal sensor do not reflect the temperature at the electrode/tissue interface and instead more likely reflect the temperature of the blood pool surrounding the electrode. Power delivery control based on such temperatures may lead to overheating of the electrode/tissue interface and the formation of coagulum.
Hence, those skilled in the art have recognized a need for providing an EP catheter capable of significantly reducing the possibility of coagulum due to electrode overheating regardless of the position of the thermal sensor relative to the tissue. The invention fulfills these needs and others.
SUMMARY OF THE INVENTION
Briefly, and in general terms, the invention is directed to an ablation catheter having one or more electrodes partially coated with a dielectric material. The non-coated portion of the electrode defines a window through which ablation energy is transferred. One or more thermal sensors are located within the window to prov
Bowe Wade A.
Calhoun Jeffrey A.
Hall Jeffrey A.
Simpson John A.
Cardiac Pacemaker, Inc.
Fulwider Patton Lee & Utecht LLP
Peffley Michael
Vrettakos Peter
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