Surgery – Instruments – Electrical application
Reexamination Certificate
1996-02-21
2001-06-05
Cohen, Lee (Department: 3739)
Surgery
Instruments
Electrical application
C606S034000, C600S374000, C607S099000, C607S122000
Reexamination Certificate
active
06241724
ABSTRACT:
FIELD OF THE INVENTION
In a general sense, the invention is directed to systems and methods for creating lesions in the interior regions of the human body. In a more particular sense, the invention is directed to systems and methods for ablating heart tissue for treating cardiac conditions.
BACKGROUND OF THE INVENTION
Physicians frequently make use of catheters today in medical procedures to gain access into interior regions of the body. In some procedures, the catheter carries an energy emitting element on its distal tip to ablate body tissues.
In such procedures, the physician must establish stable and uniform contact between the energy emitting element and the tissue to be ablated. Upon establishing contact, the physician must then carefully apply ablating energy to the element for transmission to the tissue.
The need for precise control over the emission of ablating energy is especially critical during catheter-based procedures for ablating heart tissue. These procedures, called electrophysiology therapy, are becoming increasingly more widespread for treating cardiac rhythm disturbances, called arrhythmias.
Today, cardiac ablation procedures typically use radiofrequency (RF) energy to form a lesion in heart tissue.
Conventional cardiac ablation systems designed to cure re-entrant supra ventricular tachycardia (SVT), often create lesions in myocardial tissue with a penetration depth of about 3 to 5 mm and a lesion volume of less than 0.2 cm
3
, depending upon the size of the electrode and the amount of power that is applied.
However, to consistently cure MVT by ablation, a penetration depth greater than 3 to 5 mm and a lesion volume of at least 1 cm
3
is estimated to be required.
The solution may lie in larger electrodes and higher power systems. Yet, implementing this solution may itself pose additional problems.
The amount of RF energy that must be conveyed to conventional electrodes to create even small therapeutic lesions is already quite high (upwards to 50 watts or more). This is because conventional RF emitting electrodes are very inefficient. Only about 25% of the RF energy delivered to the electrode is actually directed into the heart tissue. The rest of the RF energy is dissipated into the circulating blood pool within the heart.
As a result, finding a predictable relationship between required RF power input and lesion volumes is often problematic. Not only are the power output to input efficiencies quite low, but they are also highly variable among patients.
Furthermore, the delivery of even larger amounts of RF energy to conventional electrodes means the dissipation of even larger amounts of energy into the blood pool. The effects of local blood heating, like the creation of thrombotic emboli, become more pronounced.
There is a need for energy emitting electrodes that more uniformly direct larger amounts of energy into the tissue, and not into the surrounding blood pool.
There is also a need for energy emitting electrodes that require less input power to create therapeutic lesions, regardless of their size.
SUMMARY OF THE INVENTION
The invention provides systems and methods that simplify the creation of lesions in body tissue, such as in the heart.
One aspect of the invention provides a multiple electrode array for ablating tissue in a body. The array comprises a support body having an axis. The body carries at least two electrode segments that are circumferentially spaced from each other about the body axis. Insulation on the support body electrically and thermally isolates the separated electrode segments from each other. Signal wires attached to the separated electrode segments convey ablating energy independently to the separated electrode segments.
Because of its segmented structure, the array may be placed with a single electrode segment in contact with tissue. Alternatively, two or more segments may contact the tissue at one time. Because each segment is electrically isolated, and because each segment is independently served by its own signal wire, a physician can operate an ablation energy generator to selectively channel the ablation energy only to the segments actually contacting the tissue.
A segmented electrode element provides significant improvements in lesion generation effectiveness and efficiency.
Another aspect of the invention provides a segmented electrode array that includes an orientation sensing mechanism on the support body for sensing the orientation of the separated electrode segments relative to tissue. The orientation sensing mechanism senses among the electrode segments which electrode segment is in contact with tissue and which electrode segment is not in contact with tissue.
Another aspect of the invention provides a system that integrates the segmented electrode array, an orientation sensing mechanism, and an ablating energy source. In this arrangement, the ablating energy source conveys ablating energy only to the electrode segment or segments sensed as being in contact with tissue.
Another aspect of the invention provides a method of ablating tissue in a body. The method comprises the steps of introducing a multiple electrode array comprising at least two separated and electrically isolated electrode segments. The method senses the orientation of the separated electrode segments relative to tissue and generates an orientation signal that identifies which one of the electrode segments contacts tissue and which one of the electrode segments does not. The method conveys ablating energy only to the electrode segment or segments identified as contacting tissue and not to the electrode segment or segments identified as not contacting tissue.
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Amirana Omar M.
Fleischman Sidney D.
Houser Russell A.
Swanson David K.
Cohen Lee
EP Technologies, Inc.
Lyon & Lyon LLP
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