Surgery – Instruments – Electrical application
Reexamination Certificate
1998-04-01
2001-03-06
Dvorak, Linda C. M. (Department: 3739)
Surgery
Instruments
Electrical application
C606S042000, C606S045000, C607S102000
Reexamination Certificate
active
06197023
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an apparatus for catheter ablation in general and for radiofrequency catheter ablation of preferably living endomyocardial tissue in particular, and also to a corresponding ablation catheter and a process for its operation.
2. Discussion of Relevant Art
In the treatment of cardiac arrhythmias which are produced by electrically autonomous tissue and in particular by tissue which is not subject to the central excitation control of the heart, thermal coagulation of the tissue concerned has been shown to be successful, and is well-established in the field. In this procedure, the ablation catheter is pushed endocardially into the heart, and energy is delivered to the concerned tissue from an electrode at the tip of the catheter or from electrodes arranged along the longitudinal axis of the catheter, so that a local coagulation takes place and the tissue region causing the disturbed functioning is electrically isolated. In this procedure, the energy is usually delivered continuously to the electrode by means of a high frequency generator at frequencies of 300-700 kHz, and a coagulation scar is thus produced to a depth of 3-5 mm.
However, it is disadvantageous for this process that the temperature of some portions of the catheter is so high that blood coagulates and adheres to the catheter. Further ablation is thereby hindered, and cleaning of the electrode is necessary. The subsequent withdrawal and reinsertion of the catheter represents an additional stress for both the patient and the surgeon. Furthermore, there is great danger of thrombosis due to the coagulated blood. On the other hand, there is a requirement to further increase the energy delivered to the tissue, in order to reach, with greater depths of lesion, arrhythmogenic tissue regions which lie deep in the myocardium.
SUMMARY OF THE INVENTION
The invention has as its object at least to mitigate such disadvantages in the catheter ablation of tissue, and to control the delivery of energy to the tissue to be ablated so that a predetermined coagulation temperature is reached within the concerned tissue region.
This object is attained in a surprisingly simple manner by a radio frequency catheter ablation apparatus having an ablation catheter, a connection to a high frequency generator, and to controlled or regulated high frequency ablation equipment associated with the catheter. The catheter has at least one electrode for ablation of tissue by irradiation of ablating power, and at least one temperature sensor associated with the electrode for sensing the temperature of the electrode. A sensing device senses a parameter that is related to a temperature difference between the temperature measured at the electrode and the temperature in tissue in the vicinity of the electrode.
The invention includes the highly surprising knowledge that the temperature measured at the catheter does not agree in every case with the internal tissue temperature, even when the catheter is closely adjacent to the tissue or is surrounded by it. In the meaning according to the invention, but without any limitation of generality thereby, the internal tissue temperature is the temperature within a tissue region which is 0-20 mm distant from the respective catheter electrode, preferably about 0-8 mm distant.
It was furthermore established that in pulsed ablation processes at higher power levels, i.e., at power levels above about 70 Watts and catheter temperatures above 60° C., the internal tissue temperature can be distinctly higher than the catheter temperature, even to the extent that vaporization or the formation of steam bubbles within the tissue can occur, which in some circumstances can have lethal consequences.
Furthermore the electrode temperature according to the invention, even with high internal tissue temperatures, can be kept in a region in which blood does not coagulate at the electrode and adhere to it. Here use was made of the knowledge that a much greater delivery of energy to the concerned tissue takes place, at a predetermined maximum electrode temperature, when an ablation catheter is used which is operated in a pulsed mode, in comparison with a continuously operated ablation catheter.
For example, about double the energy can be delivered to a tissue section until the predetermined electrode temperature of 60° C. is reached, when using a pulse operated ablation catheter with a pulse duty factor of one to one, than when using a continuously operated ablation catheter. The higher delivery of energy furthermore enables deeper depths of lesion to be attained, so that arrhythmogenic tissue regions which lie deeper in the myocardium can also be included. The required depth of lesion is reached more rapidly by means of the increased energy delivery; depths are even thereby reached which the continuous process cannot reach, and moreover the time required is reduced.
The catheter can advantageously include several selectively drivable electrodes with associated temperature sensors, whereby a linear ablation can be effected. This results in a shorter treatment time and hence reduced stress for the patient, and the separation of the concerned tissue section from the primary conduction system can potentially be more effectively insured by means of such an interruption of the conduction system than by the conventional process.
The circumstance that the internal tissue temperature often reaches uncontrolled high temperatures during pulse operation was taken into account in that, for each ablation catheter, a set of parameters is recorded in a test setup, with simultaneous measurement of the internal tissue temperature in a test body, and the result serves as a basis for calculating the internal tissue temperature for the subsequent ablation in the human heart. The occurrence of uncontrolled internal tissue temperatures which endanger the patient's life can thereby be substantially prevented.
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Dvorak Linda C. M.
Gibson Roy
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