Surgery – Instruments – Electrical application
Reexamination Certificate
2000-12-28
2004-06-22
Robinson, Daniel (Department: 3742)
Surgery
Instruments
Electrical application
C219S494000
Reexamination Certificate
active
06752804
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 ablation system having multiple-sensor electrodes and a controller for assessing the position of the electrode and the sensors relative to the biological tissue and the adequacy of the energy being applied.
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 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.
During ablation, portions of the electrodes are typically in contact with the blood, so that it is possible for clotting and boiling of blood to occur if those electrodes reach an excessive temperature. Both of these conditions are undesirable. Clotting is particularly troublesome at the surface of the catheter electrode because the impedance at the electrode rises to a level where the power delivery is insufficient to effect ablation. The catheter must be removed and cleaned before the procedure can continue. Additionally, too great a rise in impedance can result in tissue dessication and thrombus formation within the heart, both of which are also undesirable. Further, too great a temperature at the interface between the electrode and the tissue can cause the tissue to reach a high impedance which will attenuate and even block the further transmission of RF energy into the tissue thereby interfering with ablation of tissue at that location.
To avoid these detrimental conditions, RF ablation catheters for cardiac applications typically provide temperature feedback during ablation via a thermal sensor such as a thermocouple. In the case where a catheter has a band electrode, such as for the treatment of atrial fibrillation by the ablation of tissue, the temperature reading provided by a single thermal sensor mounted to the band along the catheter's outside radius of curvature, may not accurately represent the temperature of the electrode/tissue interface. Typically the side of the band which is in direct contact with the tissue becomes significantly hotter than the rest of the band electrode that is cooled by the blood flow. Thus, the closer the thermal sensor is to the electrode/tissue interface, the more closely the temperature reading provided by the thermal sensor reflects the temperature of the tissue.
The position of the thermal sensor relative to the electrode/tissue interface is influenced by the rotational orientation of the catheter. If the catheter is oriented so that the single thermal sensor is not in contact with the tissue during the application of ablation energy, not only would there be a time lag in the sensor reaching the tissue temperature, but due to the effect of the cooling blood flow, the sensor reading may never approach the actual tissue temperature.
To overcome the effect that the rotational orientation of the catheter has on temperature sensing, two thermal sensors may be used. These thermal sensors are positioned at different locations on the band electrode and are also located about the catheter's outside radius of curvature, with one electrode being positioned on each side of the radius of curvature. As shown in
FIGS. 15 and 16
, the outside radius of curvature is the longitudinal line positioned at the outer most point of the outer half of the catheter, most distant from a reference center point of the catheter distal tip curve. Ideally, contact between the catheter and the tissue occurs along this longitudinal line, i.e., the outside radius of curvature. In such catheters it is generally assumed that at least one of the two thermal sensors will be located directly upon the electrode/tissue interface during ablation. Accordingly, while both thermal sensors provide temperature readings, only the highest measured temperature is of clinical interest. This is because the highest sensor reading is expected to reliably represent the electrode/tissue interface temperature.
In a catheter having two thermal sensors, it is still possible that neither sensor is positioned at the electrode/tissue interface. This may occur in situations where the contour of the anatomical structure in which the catheter is placed is such that the band electrode does not contact the tissue. This may also occur where the distal end of the catheter is misoriented such that while tissue contact is made, it is not made along the outside radius of curvature of the catheter. It may also occur where, due to excessive axial twisting of the distal end of the catheter, some
Hall Jeffrey A.
Sherman Marshall L.
Simpson John A.
Wood David S.
Cardiac Pacemakers Inc.
Fulwider Patton Lee & Utecht LLP
Robinson Daniel
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