Surgery – Instruments – Electrical application
Reexamination Certificate
2001-03-01
2003-12-23
Dvorak, Linda C. M. (Department: 3739)
Surgery
Instruments
Electrical application
C606S034000, C607S101000, C607S102000
Reexamination Certificate
active
06666862
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to an electrophysiological (“EP”) system and method for providing energy to biological tissue within a biological site, and more particularly, to an EP system and method for controlling the delivery of RF energy to the tissue based on the flow of fluid through the biological site.
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.
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 generally occurs.
Blood coagulation is a major limitation/complication associated with RF ablation therapy. Coagulation can lead to thromboembolism and also form an insulating layer around the electrode hindering further energy delivery required for ablation therapy. Thus, heating of blood is a major concern for ablation safety and efficacy. During ablation therapy, it is known that the temperature of blood near an electrode is dependent on the blood flow rate. Low blood flow results in reduced convective heat dissipation within the blood pool around the electrode and thus higher blood temperature. Conversely, high blood flow rate results in increased convective heat dissipation within the blood pool around the electrode and thus a lower blood temperature.
Conventional RF ablation systems fail to account for the effect that varying blood flow rates have on blood, electrode and tissue temperatures, which can be substantial. During an ablation procedure, conventional systems apply a level of RF energy to the electrodes sufficient to elevate the tissue temperature to a level that causes the tissue to become non-viable. The level of RF energy is generally constant regardless of the blood flow rate and is only adjusted if the system employs some type of temperature feedback control. In these systems an attempt is made to guard against blood coagulation and coagulum formation by monitoring the temperature of the electrodes, usually using a thermocouple attached to the electrode. When a threshold temperature is reached, the application of RF energy is either reduced or shut off. However, such thermocouples are generally located at the tissue/electrode contact location, which can have a significantly different temperature than the opposite side of the electrode that is in the blood pool.
Such systems tend either to have a high incidence of coagulation or to operate inefficiently. Coagulation is likely to occur in these systems when the RF energy delivered to the electrode is set to an ablation-inducing level during periods of high-blood flow. The temperature sensing thermocouple does not provide the system with sufficient information about the temperature of the blood pool. Consequently, the convective heat dissipation effect of the high-blood flow keeps the blood pool around the electrode cool and ablation is efficiently accomplished, however, during periods of low-blood flow, the reduced convective heat dissipation allows the blood pool to heat. Over the course of an ablation procedure, the cumulative effect of the periods of low-blood flow is likely to result in coagulum formation.
In order to avoid coagulation the energy level may be reduced. This, however, tends to lead to an inefficient ablation procedure. If the energy level is set to induce ablation during periods of low flow, the convective heat dissipation effect during periods of high-blood flow reduces the electrode temperature and thus the tissue temperature to a non-ablative level. The culmination of these periods of non-ablative temperature levels at best increases the amount of time necessary to achieve an ablation-inducing temperature and thus the overall procedure time, and at worst prevents the electrode from ever reaching an ablation-inducing level.
Hence, those skilled in the art have recognized a need for a RF ablation system and method that controls and adjusts the RF energy level delivered to tissue within a biological site based on the flow rate of fluid through the site. The invention fulfills this need and others.
SUMMARY OF THE INVENTION
Briefly and in general terms, the present invention is directed to a system for, and a method of, controlling the delivery of energy to biological tissue during an ablation procedure based on the flow of fluid through the biological site.
In one aspect, the invention relates to a system for applying energy to biological tissue within a biological organ having fluid flowing therethrough. The system includes a generator for providing energy and a catheter carrying an electrode system at its distal end. The distal end of the catheter is adapted to be positioned in a biological organ and the electrode system is adapted to receive energy from the generator. The system further includes a device adapted to provide flow rate information indicative of the flow rate of the fluid through the biological organ and a processor adapted to receive the flow rate information. The processor is adapted to assess whether the fluid-flow rate is high or low and control the generator s
Jain Mudit K.
KenKnight Bruce
Morris Milton M.
Cardiac Pacemakers Inc.
Dvorak Linda C. M.
Fulwider Patton Lee & Utecht LLP
Ruddy David M.
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