# Patent

## Title
Radio frequency ablation servo catheter and method

## Abstract

A system that interfaces with a workstation endocardial mapping system allows for the rapid and successful ablation of cardiac tissue. The system allows a physician to see a representation of the physical location of a catheter in a representation of an anatomic model of the patient's heart. The workstation is the primary interface with the physician. A servo catheter having pull wires and pull rings for guidance and a servo catheter control system are interfaced with the workstation. Servo catheter control software may run on the workstation. The servo catheter is coupled to an RF generator. The physician locates a site for ablation therapy and confirms the location of the catheter. Once the catheter is located at the desired ablation site, the physician activates the RF generator to deliver the therapy.

## Background
CROSS REFERENCE
The present invention is a utility patent application based upon U.S. Provisional Application No. 60/575,741, filed May 28, 2004, which is incorporated by reference herein in its entirety.


FIELD OF THE INVENTION
The present invention relates generally to radio frequency ablation catheter systems and more particularly to an interactive and automated catheter for producing lesions to treat arrhythmias in the atrium of a patient's heart.
BACKGROUND OF THE INVENTION
Many atrial arrhythmias are caused by anatomical accessory pathways in the heart, which provide spurious conduction paths. Conduction of electrical depolarization's along these pathways within a chamber gives rise to arrhythmias. Although drugs have been used to treat such arrhythmias for many years, cardiac ablation, or destruction of localized regions of tissue, can provide a permanent cure for the patient. For this reason cardiac ablation is preferred in many instances. This treatment is especially preferred for patients that experience detrimental effects from drugs.
Cardiac ablation has traditionally been a tedious procedure performed under fluoroscopy by a physician who sequentially maps the electrical potentials within the heart using a manually directed EP catheter. Once an appropriate site has been selected identified and selected for ablation, RF energy is delivered to the site. Ablation energy is typically delivered through the same catheter used to “map”. The purpose of the ablation is to destroy a small bolus of tissue at the location. This tissue lesion can no longer conduct and the arrhythmia is interrupted and the arrhythmia stops.
One common intervention is ablation around the annulus or the ostium of the pulmonary vein that is located in the left atrium. However, navigating to this location reliably and sequentially and delivering electrical energy is an extremely tedious procedure requiring substantial amount of skill and time to complete successfully.
For this reason there is a continuing need to improve catheter technology.
SUMMARY OF THE INVENTION
The present invention provides a system that allows for the automated rapid and successful ablation of cardiac tissue. The overall system interfaces with an Endocardial Solutions Ensite “work station” endocardial mapping system of the type sold by Endocardial Solutions, Inc. of St. Paul, Minn., or other equivalent devices.
The “Ensite” system is preferred as it includes a “NavX” feature that allows the physician to see a representation of the physical location of his catheter in a presentation of an anatomic model of the patient's heart.
The system includes a “servo catheter” and a servo catheter control system that are interfaced with the work station. The work station is the primary interface with the physician and it is anticipated that the servo catheter control software will run on the work station. The servo catheter will also be coupled to a conventional RF generator.
In use the physician will locate site for ablation therapy and then he will confirm the location of the catheter which will automatically navigate to the lesion site desired by the physician. Once the catheter is located at that desired point or site the physician will activate the RF generator to deliver the therapy.



BRIEF DESCRIPTION OF THE DRAWINGS
Throughout the several drawings identical reference numerals indicate identical structure wherein:
FIG. 1 is a schematic representation of the overall system;
FIG. 2 is a schematic representation of a portion of the overall system;
FIG. 3 is a schematic representation of an image displayed by the system;
FIG. 4A is a flow chart representation of a method of the system;
FIG. 4B is a flow chart representation of a method of the system;
FIG. 5 is a representation of a servo catheter of the system; and,
FIG. 6 is a representation of a servo catheter of the system.



DETAILED DESCRIPTION
Overview
For purposes of this disclosure the NavX features of the Ensite system as sold by ESI of St Paul Minn., allows for the creation of a chamber geometry reflecting the chamber of interest within the heart. In a preferred embodiment a mapping catheter is swept around the chamber by the physician to create a geometry for the chamber. Next the physician will identify fiducial points in the physical heart that are used to create a base map of the heart model. This base map may be merged with a CT or MRI image to provide an extremely high resolution, highly detailed anatomic map image of the chamber of the heart. Or in the alternative the base map may be used for the method. The physician identifies regions of this model heart for ablation by interacting with a computer terminal and for example using a mouse to lay down a collection of target points which he intends to ablate with RF energy.
In summary the servo catheter is also interfaced with the Ensite system and makes use of the NavX catheter navigation and visualization features of NavX. In operation the physician navigates the servo catheter to the approximate location of the therapy and a relatively complicated control system is invoked that navigates the servo catheter tip to various locations sequentially identified by the physician. Once in place and after its position is verified the physician will activate the RF generator to provide the ablation therapy.
Servo Catheter
The catheter has a number of attributes that permit the device to carry out this function. An illustrative and not limiting prototype version of the device is seen in FIG. 5 and FIG. 6. The catheter 100 has been constructed with eight pull wires (of which 4 are shown for clarity) and two associated pull rings labeled 102 and 104 in the figures.
The pull wires typified by pull wire 106 and 108 are manipulated by servo mechanisms, such as stepper or driven ball screw slides illustrated in FIG. 1. These mechanisms displace the wire with respect to the catheter body 110 and under tension pull and shape the catheter in a particular direction. The use of multiple wires and multiple pull rings allows for very complex control over the catheter's position, shape and stiffness, all of which are important to carry out the ultimate therapy desired by the physician. Multiple pull rings and multiple individual wires permits control over the stiffness of the catheter which is used to conform the shape of the catheter so that the entire carriage may be advanced on a ball screw to move the catheter against the wall of the heart.
At least one force transducer 112 is located within the catheter provide feedback to the control system to prevent perforation of the heart and to otherwise enhance the safety of the unit. Preferably the force transducer takes the form of a strain gauge 112 coupled to the control system via connection 120.
The catheter distal tip will carry an ablation electrode 124 coupled via a connection not shown to the RF generator as is known in the art. It is preferred to have a separate location electrode 126 for use by the Ensite system as is known in the art. Once again no connection is shown to simply the figure for clarity.
As seen in FIG. 6 pulling on pull wire 108 deflects the distal tip while pulling on pull wire 106 deflects the body 110 of the catheter. Since each wire is independent of the others the computer system may control both the stiffness and deflection of the catheter in a way not achieved by physician control of the wires. In general the physician will use a joystick of other input device to control the catheter. However, this control system also invokes many of the automated procedures of the servo catheter and is not strictly a direct manipulator.
Although robotic control has made great headway in surgery most conventional systems use a stereotactic frame to position the device and the coordinate systems with respect to the patient. One challenge of the current system is the fact that the target tissue is moving because the heart is beating and the catheter within the heart is displaced and moved by heart motion as well so that there is no permanently fixed relationship between the catheter and its coordinate system, the patient and its coordinate system, and the patient and its coordinate system at the target site. This issue is complicated by and exacerbated by the fact that the map may not be wholly accurate as well, so the end point or target point's location in space is not well resolved.
Operation Overview
Turning to FIG. 1 there is shown a patient's heart 10 in isolation. A series of patch electrodes are applied to the surface of the patient (not shown) typified by patch 12. These are coupled to an Ensite catheter navigation system 14 which locates the tip of the Servo catheter 16 in the chamber 18 of the patient's heart. The Ensite system is capable of using this catheter or another catheter to create a map of the chamber of the heart shown as image 20 on monitor 22 of a computer system. In operation the physician interacts with the model image 20 and maps out and plans an RF ablation intervention that is applied to the Servo catheter 16 through its proximal connection to the Servo catheter interface box 24. The interface box allows RF energy from generator 26 to enter the catheter upon the command of the physician and ablate tissue in the cardiac chamber. Critical to the operation of the servo catheter is the translation mechanism 28, which provides a carriage for translating the catheter proximal end advancing or retracting the catheter from the chamber as indicated by motion arrow 30. An additional group of sensors and actuators or other servo translation mechanism 32 are coupled to the proximal end of the catheter 16 to allow the device to be steered automatically by software running on the Ensite 14 workstation.
Thus, in brief overview, the physician navigates the catheter into the chamber of interest, identifies locations of interest within that chamber which he desires to ablate, then the Servo mechanism moves the catheter to various locations requested by the physician and once in position the physician administers RF radiation to provide a therapeutic intervention.
FIG. 2 shows the interaction of the physician with the heart model. The locations for ablation are shown on the map 20 as X's 32 which surround an anatomic structure that may be, for example, the pulmonary vein 34. These locations are typically accessed on the map image through a mouse or other pointer device 36 so that the physician may act intuitively with the model. As is clear from the Ensite operation manual the catheter 16 may also be shown on the image to facilitate planning of the intervention. Turning to FIG. 3 the servo catheter 16 has been activated and the catheter has been retracted slightly as indicated by arrow 41 and has been manipulated to come into contact with the cardiac tissue at location 40. In this instance the physician is in a position to perform his ablation.
The control system to achieve this result is shown in FIG. 4A and FIG. 4B which are two panels of a software flow chart describing software executed by the Ensite work station.
Turning to FIG. 4a, initially the catheter is placed in the desired heart chamber as seen in FIG. 2 by the positioning of catheter 16 as represented on the Ensite work station within the chamber of the heart 20. This process occurs after the creation of the chamber geometry. In block 202 the Ensite system determines the location of the location ring of catheter 16 in the chamber and in process 204 a small motion is initiated by the operation of the steppers 32 controlling the various pull wires of the catheter. The Ensite system tracks the motion of the location electrode and establishes a relationship between the operation of the various pull wires and motion in the chamber. It is important to note that this process eliminates the need to keep track of the X, Y, Z references of the body and the catheter. In process 206 the physician manipulates the joystick or other control mechanism and places the target location, for example target location 32, around an anatomic feature of interest, for example the OS of the pulmonary vein. The user then activates a “go” command on the workstation and the catheter 16 automatically navigates to the location 32 by measuring the difference between its current position and the desired location position in block 210. If it is within 0.5 millimeters or so, the process stops in block 212. However, if the catheter is farther away from the target location than 0.5 millimeters, the process defaults to step 212 wherein a displacement vector is calculated in process 212. In process 214 the displacement vector is scaled and in process 216 an actuation vector is computed to drive the catheter toward the location. In process 218 the actuation vector is applied to the pull wires 32 and to the carriage 28 to move the catheter tip toward the desired location. After a short incremental motion in process 220 a new location for the catheter is computed and the process repeats with comparison step 210. It is expected that in most instances the algorithm will converge and the catheter will move smoothly and quickly to the desired location. However, after a certain number of tries if this result is not achieved it is expected that an error condition will be noted and the physician will reposition the catheter manually and then restart the automatic algorithm.

## Claims

1. A system for automated delivery of a catheter to a predetermined cardiovascular target site, said system comprising:
a catheter having a distal end, a proximal end, a catheter body and at least one catheter electrode proximate said distal end;
a plurality of paired electrodes adapted to be configured in a predetermined orientation relative to said cardiovascular target site;
a modeling system that uses a plurality of electrical signals generated by said at least one catheter electrode and said plurality of paired electrodes to create a model of said cardiovascular site;
a servo translation mechanism operably coupled to said catheter, said servo translation mechanism providing for at least three degrees of freedom of motion of said distal end of said catheter; and
control software that utilizes said model of said cardiovascular site and said at least one catheter electrode to monitor and direct the location of said distal end of said catheter to said predetermined cardiovascular target site,
wherein said catheter further comprises:
a plurality of spaced-apart pull rings; and
a plurality of pull wires connected to each of the pull rings and operably coupled to the servo translation mechanism.

2. The system of claim 1, wherein said at least one catheter electrode is selected from the group consisting of: a location electrode, an ablation electrode, and combinations thereof.

3. The system of claim 1, wherein said catheter further comprises at least one force transducer.

4. The system of claim 3, further comprising an anatomic image of a heart, wherein the anatomic image of the heart is created by sweeping the catheter around a chamber of the heart and using signals created by the force sensor to indicate when the catheter has reached a boundary point of the heart chamber.

5. The system of claim 1, wherein the control system uses the servo translation mechanism to control a plurality of pull wires connected to a first pull ring to define a first fulcrum about which the control system may pivot the catheter by controlling one or more pull wires connected to a second pull ring which is spaced a predetermined distance from the first pull ring.

6. A servo catheter system, comprising:
a catheter having a distal end, a proximal end, a catheter body and at least one catheter electrode proximate said distal end;
a modeling system that uses electrical signals generated by said at least one catheter electrode to create a model of said cardiovascular site, wherein said modeling system may be used to identify a plurality of target points in the cardiovascular site;
a servo translation mechanism operably coupled to said catheter, said servo translation mechanism providing for at least three degrees of freedom of motion of said distal end of said catheter; and
control software that utilizes said model of said cardiovascular site and that utilizes information measured from said at least one catheter electrode to direct the location of said distal end of said catheter to at least one of the plurality of target points in the cardiovascular site,
wherein said catheter further comprises:
a plurality of pull rings spaced at least one predetermined distance from each other; and
a plurality of pull wires connected to each of the pull rings and operably coupled to the servo translation mechanism,
wherein the pull rings and pull wires are adapted to control stiffness and shape of the catheter.

7. A method of locating and controlling a catheter within a patient, said method comprising the steps of:
providing a catheter having a distal end, a proximal end, a catheter body, a force sensor, a plurality of spaced-apart pull rings, a plurality of pull wires connected to each of the pull rings, and a catheter electrode proximately located to the distal end;
mechanically coupling a servo translation mechanism to at least the plurality of pull wires;
sweeping the catheter in a heart chamber, monitoring signals created by the force sensor to determine when the catheter has reached boundary points in the heart chamber, and recording the locations for a plurality of boundary points to create an anatomic map image of the heart chamber;
displaying the anatomic map image of the heart chamber;
accepting input from a user who identifies at least one target where the distal end of the catheter is to be positioned;
using a catheter location system to generate information reflecting the location of the catheter in a patient;
activating the servo translation mechanism to move the distal end of the catheter to the at least one target in the heart chamber; and
utilizing the location information generated by the catheter location system to provide feedback to the servo translation mechanism to assist in the movement of the distal end of the catheter.

8. The method of claim 7, wherein the step of accepting input from a user who identifies at least one target comprises accepting input from a mouse or joystick to identify at least one target in the heart chamber where the distal end of the catheter is to be positioned.

9. The method of claim 7, wherein the step of using a catheter location system to generate information reflecting the location of the catheter in a patient comprises:
providing a plurality of paired electrodes configured in a predetermined orientation relative to said cardiovascular target site; and
measuring electrical signals between the plurality of paired electrodes and the catheter electrode to determine the location of the distal end of the catheter in a patient.

10. The method of claim 7, further comprising utilizing the information measured by the force sensor to provide feedback to the servo translation mechanism to assist in moving the distal end of the catheter.

11. The method of claim 7, further comprising:
initiating a small motion in the servo translation mechanism to move the catheter;
measuring an actual distance that the catheter is moved;
establishing a relationship between the servo translation mechanism and the catheter.

12. The method of claim 7, wherein the step of sweeping the catheter to create an anatomic map image comprises:
sweeping the catheter in a heart chamber;
monitoring signals created by the force sensor to determine when the catheter has reached boundary points in the heart chamber;
recording the locations for a plurality of boundary points to create a first image of the heart chamber;
receiving a second image of the heart chamber; and
combining the first and second images of the heart chamber to create an anatomic map image.

13. The method of claim 7, further comprising:
controlling a plurality of pull wires connected to a first pull ring to define a fulcrum about which the control system may pivot the catheter; and
controlling one or more pull wires connected to a second pull ring that is spaced a predetermined distance from the first pull ring in order to pivot the catheter about the fulcrum.