Surgery – Instruments – Electrical application
Reexamination Certificate
1998-12-10
2001-02-27
Dvorak, Linda C. M. (Department: 3739)
Surgery
Instruments
Electrical application
C606S032000, C606S038000, C606S041000, C606S048000, C607S101000, C607S102000
Reexamination Certificate
active
06193713
ABSTRACT:
The present invention relates to a method for the operation of a high frequency ablation instrument comprising a radiofrequency energy source having a plurality of regulatable outputs, with a plurality of electrodes being connected to its outputs. Furthermore, the invention is directed to an instrument for high frequency tissue ablation.
Ablation instruments of this kind are, for example, used for the treatment of cardiac irregularity or disordered action of the heart. For this purpose an ablation catheter having one or more electrodes is connected to a radiofrequency energy source and is, for example, introduced via a blood vessel into the interior of the heart. The electrodes provided at the end of the catheter are positioned at the desired location at the inner or outer surface of the heart, whereupon the regions standing in contact with the electrodes are thermally obliterated by the supply of radiofrequency energy.
The electrical characteristics of the treated heart tissue are so changed through the lesions which are produced in this manner that cardiac irregularities which are present are removed.
Catheters with only one electrode are poorly suited for certain types of cardiac irregularities, for which larger areas of tissue have to be obliterated, since the sequence of a plurality of point-like lesions that is required with the heart beating is generally only inadequate and only possible with a large expenditure of time. For the obliteration of larger areas of tissue, catheters having a plurality of electrodes can be used. In this arrangement it is advantageous if the energy yield for each catheter electrode can be individually adjusted so that, for example, the ideal temperature acting in the tissue can be set for each catheter electrode, despite different cooling conditions in the different electrodes, and also despite different load resistances for each catheter electrode.
The individual catheter electrodes normally cooperate with a large area electrode contacting the body of the patient to be treated, the so-called indifferent electrode, so that with an energy supply to the catheter electrodes, current in each case flows from the catheter electrodes through the body of the patient to the indifferent electrode. Since the current density is highest directly at the transition between the catheter electrodes and the tissues to be treated, as a result of the small area of the catheter electrodes, the temperature in this region is sufficiently high, with adequate energy supply, that the desired lesions are produced.
When using catheters with a plurality of electrodes, the following problem arises: Since, in dependence on the requirement, different temperatures can be necessary at different catheter electrodes, or different energies can be necessary to achieve a specific temperature, and since the load resistances which become active at the electrodes can be different, the energy yield via the individual catheter electrodes must be individually set. This leads to different voltage values and current values being necessary at the different catheter electrodes. In particular, when the catheter outputs have low output resistances, compensation currents arise between electrodes to which different voltage values are applied or with phase shifts between the output voltages. These compensation currents are currents which flow, instead of to the indifferent electrode, to another catheter electrode at which a voltage is present which differs from the voltage at the electrode from which the current emerges. If a high potential difference exists between the two catheter electrodes, then the compensation current flowing into the other electrode can lead to undesirably high current densities at this electrode, which in turn bring about undesired coagulations at this electrode. This effect is particularly notable at electrodes at which no energy transmission or only a small energy transmission is desired.
BRIEF SUMMARY OF THE INVENTION
The object of the invention is to design an instrument and a method of the initially named kind so that compensation currents between the outputs or between electrodes connected to the outputs are largely avoided. Furthermore, a continuous energy delivery should be possible. The instrument should have a high degree of efficiency and also the circuit complexity should be as low as possible.
Starting from a method of the initially named kind, the part of the object relating to the method is satisfied in that a respective power value and/or current value representative of the power and/or the current transmitted by the radiofrequency energy source is detected for each output; in that the voltage transmitted from the radiofrequency energy source is so regulated in dependence on the detected power value and/or current value that the latter corresponds substantially to a predetermined power value and/or current value; and in that a predetermined phase relationship is in each case maintained between the currents or between the voltages at the outputs of the radiofrequency energy source.
The part of the object relating to the apparatus is satisfied in accordance with the invention by an instrument of the initially named kind with at least one measurement element for detecting power values and/or current values representative for the power and/or current delivered at the respective outputs, and by at least one regulating element connected to the measurement element for the regulation of the voltage delivered by the radiofrequency energy source in dependence on the detected power value and/or current value applied to an actual value input of the regulating element, and on a preset power value and/or current value applied to a desired value input of the regulating element, with the currents or voltages at the outputs of the radiofrequency energy source each having a predetermined phase relationship to one another.
The apparatus of the invention is thus so designed that its outputs have the behavior of a current or power source. In this way compensatory currents which would, for example, flow from an electrode with a higher voltage to an electrode with a lower voltage and lead to a feedback into this electrode are avoided. This feedback would lead to a situation in which, in an extreme case, a current of higher magnitude undesirably flows through the compensatory current to this electrode, which brings about an undesired coagulation at this electrode. For example, under some circumstances, the compensation current can be subtracted from the suppressed output current of the affected electrode, which can lead to a situation in which the direction of action of the current flowing through the affected electrode is reversed.
Through the current or power regulation in accordance with the invention, this deviation in the desired value is directly counteracted by follow-up regulation, for example, by an increase of the output voltage, so that the desired current again flows through the electrode.
In accordance with a preferred embodiment of the invention, the rf-energy source comprises at least one regulatable DC voltage source, which consists, for example, of a non-regulated DC voltage source and a voltage regulator, and at least one switching stage connected to the DC voltage source, with the or each switching stage being controlled by an in particular periodic switching signal for the generation of the rf output voltage, and with the voltage transmitted by the DC voltage source being regulated for the regulation of the voltage transmitted by the rf energy source. In this manner a particularly simple and cost favorable design of an instrument formed in accordance with the invention is possible. the switching signal thereby normally consists of rectangular pulses, with the frequency of the switching signal typically lying in the range from 300 to 1000 kHz.
In a further advantageous embodiment of the invention, the power transmitted by the DC voltage source and/or the current transmitted by the DC voltage source are detected, so that the power and/or current detection takes
Geistert Wolfgang
Uphoff Peter
Dvorak Linda C. M.
Fitch Even Tabin & Flannery
Ruddy David M.
Sulzer Osypka GmbH
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