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 . 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 fig5 and fig6 . 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 fig1 . 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 &# 39 ; 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 fig6 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 &# 39 ; s location in space is not well resolved . turning to fig1 there is shown a patient &# 39 ; 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 &# 39 ; 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 . fig2 shows the interaction of the physician with the heart model . the locations for ablation are shown on the map 20 as x &# 39 ; 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 fig3 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 fig4 a and fig4 b which are two panels of a software flow chart describing software executed by the ensite work station . turning to fig4 a , initially the catheter is placed in the desired heart chamber as seen in fig2 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 .
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 &# 39 ; 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 .