Surgery – Instruments – Electrical application
Reexamination Certificate
2002-04-26
2004-03-23
Gibson, Roy D. (Department: 3739)
Surgery
Instruments
Electrical application
C128S898000
Reexamination Certificate
active
06709432
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to ablation methods and apparatus, e.g., such as those used for cardiac therapy. More particularly, the present invention pertains to apparatus and methods that use monitoring of acoustic energy to control and/or provide information regarding ablation processes.
BACKGROUND
Catheters for electromagnetic ablation are known and are commonly used to treat various diseases and medical disorders. Typically, the catheter includes an energy-delivering electrode that is coupled to a source of electromagnetic energy, e.g., an electrosurgical generator. Other electrodes can be proximally positioned on the catheter and can be used for sensing and other related electrical purposes. The generator energizes the electrode, which then transfers the energy to tissue disposed adjacent thereto. The surgical energy is typically applied to the tissue at a selected level and for a selected duration to effect a biological change in the tissue.
In prior procedures, the ablation catheter is employed to alter tissue. In order to ablate the tissue, electromagnetic energy is applied to create a lesion via the energy-delivering electrode without regard to the specific level of electromagnetic energy supplied by the generator. In situations where too much electromagnetic energy is delivered to the tissue during the electrosurgical procedure, the tissue “pops,” thus indicating the application of an excessive amount of energy.
As such, when the ablation electrode has firm contact with tissue and high power is applied, an undesirable crater may be formed at the contact site. When crater formation occurs, electromagnetic energy directed by the ablation electrode causes cells within the tissue to explode, thus creating the popping sound that may even be heard outside the patient's body. Crater formation may cause an uncontrolled high-volume lesion. To further patient safety, prevention of crater formation is desired because it is unknown how much of an effect crater formation has on the occurrence of thromboembolic incidents.
In other words, high-strength electromagnetic energy can cause tissue cells to be undesirably destroyed during certain medical procedures, e.g., ablation. As such, the delivery of such energy needs to be effectively controlled.
Further, electrosurgery cutters and ablation catheters use such electromagnetic energy. While a cut with an electrosurgical cutter is very deep and performed relatively fast, an ablation lesion formed by an ablation catheter should be precise. In other words, lesion size should also be controlled, and at least one way to control lesion size is to control the delivery of the energy to the ablation site.
Therefore, for at least the above reasons, some ablation systems known in the art include sophisticated power control systems. Such control systems use various techniques to monitor the ablation process and control the delivery of energy to the desired ablation site.
For example, catheters including temperature measurement sensors allow for control of an ablation energy generator such that an appropriate constant temperature of the ablation electrode can be maintained. However, when the temperature is low, the lesion may not be sufficient to effectively destroy the tissue. If the temperature rises too high, e.g., above 70 degrees Celsius, coagulation on the electrode may occur and undesirably increase the impedance of the ablation system.
Further, for example, U.S. Pat. No. 5,733,281 to Nardella entitled “Ultrasound and Impedance Feedback System for Use with Electrosurgical Instruments,” issued Mar. 31, 1998, discloses an electrosurgical feedback system that includes an acoustical detection element and/or an impedance determination circuit. The acoustical detection element may include an ultrasonic transducer that acoustically detects the effects of energy on tissue, such as the generation of steam created during the heating process. The acoustical detection element generates an acoustic output signal that may regulate the application of power to an energy delivering electrode. Nardella further discloses that the acoustical detection element may include a microphone coupled to a speaker for producing an audible output signal.
Various other problems may also be present in an ablation process. For example, to use the maximal amount of ablation energy, the energy-delivering electrode preferably should have an intimate contact with the cardiac tissue. Because of cardiac contractions, dislodgement of the electrode from the desired position may occur.
Electrophysiologists usually monitor intracardiac potentials to confirm the proper position (e.g., stability of) as well as the proper contact of the electrode with tissue, e.g., the endocardium. However, the intracardiac potential is discontinuous, being characterized with intrinsic deflection that is repetitive at the frequency of heart beats. Distinct ST wave amplitude elevation caused by the injury current may be used to confirm the pressure of the electrode to the cardiac muscle. However, dislodgement may also occur anywhere within the cardiac cycle while there is no intracardiac signal.
Table 1 below lists U.S. Patents relating to various ablation techniques.
TABLE 1
Patent No.
Inventor
Issue Date
5,840,030
Ferek-Petric et al.
Nov. 24, 1998
5,733,281
Nardella
Mar. 31, 1998
4,763,646
Lekholm
Aug. 16, 1988
All documents listed in Table 1 above, and further elsewhere herein, are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Embodiments, and claims set forth below, many of the devices and methods disclosed in the documents of Table 1 and other documents incorporated by reference herein may be modified advantageously by using the teachings of the present invention.
SUMMARY OF THE INVENTION
The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the art with respect to ablation of tissue. One such problem involves the inadvertent creation of an ablation crater. Another problem involves lack of stability of an ablation catheter during ablation due to physiological events, e.g., heart contractions.
In comparison to known ablation techniques, various embodiments of the present invention may provide certain advantages. For example, the present invention provides apparatus and methods that enable a practitioner to acoustically monitor ablation of tissue and control the amount of electromagnetic energy directed to the tissue to prevent crater formation. Further, the present invention provides systems and methods that increase stability of an ablation catheter during ablation by acoustically monitoring ablation and indicating instability to the practitioner. Further, the present invention provides systems and methods for monitoring both acoustical energy and temperature during ablation to aid in preventing crater formation.
Some embodiments of the present invention may provide one or more of the following features for ablating tissue: providing a catheter including an ablation electrode; ablating tissue using an ablation electrode, wherein the ablation electrode directs electromagnetic energy to the tissue; detecting at least acoustical energy resulting from ablation of tissue (e.g., cardiac tissue); comparing detected acoustical energy to at least a portion of an ECG waveform to determine stability of a catheter; determining whether detected acoustical energy is synchronized with at least a portion of an ECG waveform; controlling electromagnetic energy directed to tissue based on comparing detected acoustical energy to at least a portion of an ECG waveform; detecting at least acoustical energy resulting from ablation of tissue using a piezoelectric transducer element; detecting an ablation temperature using a piezoelectric transducer element; controlling electromagnetic energy directed to tissue based on a detected ablation te
Gibson Roy D.
Medtronic Inc.
Soldner Michael C.
Vrettakos Peter
Wolde-Michael Girma
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