Surgery – Instruments – Electrical application
Reexamination Certificate
1999-09-24
2001-07-24
Dvorak, Linda C. M. (Department: 3739)
Surgery
Instruments
Electrical application
C606S034000, C606S042000, C606S049000
Reexamination Certificate
active
06264653
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to improvements in systems for implementing ablation procedures such as cardiac ablation procedures. More particularly, the invention concerns systems for gauging the amount or quality of the contact between body tissue and one or more electrodes supported on a catheter. The invention also concerns methods for controlling power delivery to particular electrodes on a catheter in response to tissue contact data derived from that electrode or other electrodes during the ablation procedure.
BACKGROUND OF THE INVENTION
Standard generators used in catheter ablation procedures provide radio frequency (RF) energy in a unipolar fashion between one or more electrodes supported on an ablation catheter and a ground electrode applied to the patient. The delivery of ablation energy is controlled by monitoring rises in the tissue-electrode interface temperature or tissue impedance.
Recent bench studies comparing a standard generator delivering energy simultaneously to multiple electrodes to delivering pulsed RF (PRF) energy to multiple electrodes shows that pulsing produces contiguous lesions more consistently. Conventional PRF energy delivery systems deliver packets of energy to multiple electrodes at a set frequency. Once an electrode reaches a specified temperature, excess pulsed energy is diverted to a shunt resistor. Studies suggest, however, that the convective heat loss using PRF at the electrode-tissue contact point is faster than the heat conduction within the myocardium. As a result, the peak tissue temperature achieved using PRF energy can occur at depths of approximately 2 mm below the electrode within the myocardium rather than at the electrode-tissue interface. The extent of convective heat loss into the blood pool that circulates about the indwelling ablation catheter will vary with the quality and amount of electrode-tissue contact. When a portion of the ablation electrode surface area is not in contact with tissue (“poor tissue contact”), that portion of the electrode will be exposed to the circulating blood pool, resulting in the temperature sensor on the catheter reading lower temperatures for that electrode than if a greater portion of the electrode were in good contact with the tissue. A conventional system response to the low temperature reading is the application of further PRF energy to that electrode in an attempt to reach and maintain a temperature set point.
In practice, as the temperature at an electrode reaches about 100° C., a sharp impedance rise is detectable as the blood begins to boil and the denatured plasma proteins begin to adhere to that electrode. To counter this occurrence, most generators offer an adjustable impedance cut-off point that will shut down the generator if it detects such an impedance rise (typically, a rise from about 80-100 &OHgr; to about 150-200 &OHgr;). The risk of having peak tissue temperature reached within the myocardium instead of at the electrode-tissue interface is that super heating of the myocardium can occur and go undetected (i.e., a greater temperature may exist within the body organ than was measured at the electrode/tissue interface). If such a condition is not detected or thwarted, an explosion effect can occur within the myocardium causing extensive tissue damage long before a peak temperature or impedance rise is detected.
What is needed in the art is a system and method for detecting poor tissue contact conditions. What is further needed is such a system and method that can use such data to control pulsed radio frequency energy delivered to a tissue site. The present invention satisfies these and other needs.
SUMMARY OF THE INVENTION
The invention provides methods and a system for monitoring and optionally controlling a catheter ablation procedure.
In one embodiment, the invention provides a method in which a catheter and a pulsed source of RF energy are provided. The catheter can support an arbitrary number of electrodes along its length and at least one temperature sensor. In a preferred embodiment, there are a number of temperature sensors associated with the electrodes, such as one for each electrode. During and throughout an ablation procedure, pulsed radio-frequency energy is provided to the electrodes and the number of pulses delivered to each electrode is monitored over an interval of time. The amount or quality of tissue contact is gauged in this embodiment by comparing the number of pulses delivered to a particular electrode during the interval to either the number of pulses delivered to at least one other electrode of the plural electrodes or data derived during the ablation procedure.
Further preferred features include outputting the comparison to a display, and controlling the number of pulses delivered to any particular electrode in response to the comparison.
In another embodiment, a system for monitoring contact between one or more electrodes and tissue includes a controller coupled between a source of pulsed RF energy and each of several electrodes on an ablation catheter. The controller supplies pulsed RF energy to the electrodes using a gating signal and receives temperature signals throughout the ablation procedure from temperature sensors associated with the electrodes. A counter is provided which registers the number of pulses of RF energy delivered to each electrode. Finally, a processor responds to data gathered by the counter and generates a signal that gauges the amount or quality of tissue contact at each electrode. The processor optionally governs the gating signal automatically to either limit or stop the supply of pulsed RF energy to that electrode based on the contact signals from other electrodes. As a preferred feature, the system provides a continuously updated display of the gauge of tissue contact.
REFERENCES:
patent: 5759158 (1998-06-01), Swanson
patent: 5769880 (1998-06-01), Truckai et al.
patent: 5840030 (1998-11-01), Ferek-Petric et al.
patent: 5840031 (1998-11-01), Crowley
patent: 5935079 (1999-08-01), Swanson et al.
patent: 6063078 (2000-05-01), Wittkampf
patent: 6071281 (2000-06-01), Burnside et al.
patent: 6123702 (2000-09-01), Swanson et al.
patent: 6183468 (2001-02-01), Swanson et al.
C. R. Band, Inc.
Darby & Darby
Dvorak Linda C. M.
Ruddy David M.
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