Abstract:
The control for an ablation catheter provides increased ablation catheter operation feedback and increased options for programmable control of the ablation catheter for clinicians. The control for an ablation catheter has a microcontroller containing memory, an input and output coupled to the microcontroller, a movement program, a comparison program, and an annunciating program. The movement program processes position information from the input to calculate ablation catheter movement. The comparison program compares ablation catheter movement to a predetermined control data.

Description:
RELATED APPLICATION 
   This application claims priority to provisional U.S. application Ser. No. 60/371,543 filed Apr. 11, 2002. 

   FIELD OF THE INVENTION 
   This disclosure is in the field of medical devices and specifically ablation catheters that typically use radio frequency energy to lesion tissue. 
   BACKGROUND OF THE INVENTION 
   Radio frequency (RF) ablation catheters have proven to be a very effective treatment for several cardiac tachyarrhythmias. An example of an RF ablation catheter is described in the brochure entitled Medtronic ATAKR® II Advanced RF Ablation System (2000) available from Medtronic, Inc. Minneapolis, Minn. During an ablation procedure an ablation catheter is introduced into the heart usually via the femoral vein or artery under local anesthesia. A position locating system such as described in the brochure entitled Medtronic Model 9670000 LocaLisa® Intracardiac Navigation System. Certain electrogram characteristics, recorded also via an ablation electrode and additional ring electrodes, allow the physician to locate the area of tachycardia origin and the subsequent energy delivery results in thermal destruction of the arrhythmogenic substrate. The size of the demarcated lesion can be controlled by selecting a certain target temperature and appropriate power limits. The damage of arrhythmogenic substrate is a curative treatment and results in immediate and permanent termination of the arrhythmia making any concomitant palliative treatment such as medication unnecessary. 
   The clinician typically directly controls power to the ablation catheter by control settings on the RF generator and by an on-off switch operated by the clinician&#39;s foot. Clinician direct control of the power delivered to the ablation catheter can be inadequate if the catheter dislocates from the intended ablation position. In some circumstances, ablation catheter dislocation can occur so rapidly that the clinician does not have time to properly respond. Additionally, ablation systems such as the Medtronic ATAKR® II do not provide feedback to the clinician other than ablation catheter tip temperature. Catheter dislocation during RF delivery may result in an unintentional heating of healthy non-arrhythmogenic tissue. For example, catheter ablation to treat Atrial Ventricular Nodal Reentrant Tachycardia (AVNRT) involves an ablation target close to the physiological atrio-ventricular (AV) node, and damage of healthy non-arrhythmogenic tissue in this area can result in complete AV-block and pacemaker dependency. During temperature-controlled ablation, power is continuously adjusted to maintain a preset target temperature. During catheter dislocation electrode temperature will suddenly decrease and as a consequence power will be automatically increased. Increased power to the ablation catheter results in increased electrode temperature that can create a risk to healthy tissue that might come in contact with the electrode. 
   For the foregoing reasons, there is a need for a medical ablation catheter control that provides increased ablation catheter operation feedback to the clinician and provides the clinician with increased options for programmable control of the ablation catheter. 
   SUMMARY OF THE INVENTION 
   A medical ablation catheter control provides increased ablation catheter operation feedback to a clinician and increased options for programmable control of the ablation catheter. The control for an ablation catheter has a microcontroller containing memory, an input and output coupled to the microcontroller, a movement program processing position information from the input to calculate ablation catheter movement, a comparison program to compare ablation catheter movement to predetermined control data, and an annunciating program to indicate the relation of ablation catheter movement to the predetermined control data through the output. The movement program processes position information from the input to calculate ablation catheter movement. The comparison program compares ablation catheter movement to a predetermined control data. Some embodiments of the medical ablation catheter control can include a control program to determine when ablation catheter movement exceeds a predetermined movement range. Some embodiments can include a response program to interrupt power to the ablation catheter when ablation catheter movement exceeds the predetermined movement range. Many other embodiments of the medical ablation control catheter are possible. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows an environment of a medical ablation catheter. 
       FIG. 2  shows a block diagram of a medical ablation catheter control. 
       FIG. 3  shows a block diagram of the medical ablation catheter control box. 
       FIG. 4  shows an operational flowchart of the medical ablation catheter control. 
       FIG. 5  shows a flowchart of a movement program. 
       FIG. 6  shows a first portion flowchart of a comparison program. 
       FIG. 7  shows a second portion flowchart of the comparison program. 
       FIG. 8  shows a flowchart of an annunciating program. 
       FIG. 9  shows a broad flowchart of a control program. 
       FIG. 10  shows a more detailed flowchart of the control program. 
       FIG. 11  shows a flowchart of a response program. 
       FIG. 12  shows a flowchart of a physiological movement program. 
       FIG. 13  shows a graph of electrode position changes due to physiological movement. 
       FIG. 14  shows a flowchart of a method for ablation catheter control. 
       FIG. 15  shows the experimental tank setup. 
       FIG. 16  shows an operational flowchart of the medical ablation catheter control as used in the experimental task setup in FIG.  15 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows the environment of a medical ablation catheter  20 . The medical ablation catheter  20  can be any of a variety of commercial available ablation catheters such as a Medtronic Model RF Conductr® MC available from Medtronic, Inc. Minneapolis, Minn. USA, and the like. The handle of the ablation catheter provides steering capabilities of the catheter distal tip  22 . The ablation catheter  20  is connected to a radio frequency (RF) source  24  such as a Medtronic Atakr® II RF generator and the like. The RF generator delivers RF energy typically at a frequency of 480 kHz to the distal tip  22  of the ablation catheter  20 . An indifferent electrode that is in contact with the patient&#39;s body and connected to the RF source provides the current return path. 
     FIG. 2  shows a schematic drawing of a medical ablation catheter control  26  in use. The medical ablation catheter control  26  is connected between the RF source  24  indifferent electrode input  28  and the patient indifferent electrode  30  that is in contact with the patient. Furthermore, the medical ablation catheter control  26  is connected to an electronic position detection system  32 , such as a Medtronic Model 9670000 LocaLisa® and a computer for graphical display of the electrode position. The medical ablation catheter control  26  comprises switches  34  to select operational parameters such as allowed movement boundaries and the like and indicators  36  that annunciate the status of the program residing in memory that calculates catheter  20  movement. 
     FIG. 3  shows a block diagram of the medical ablation catheter control  26 , and  FIG. 4  shows an operational flowchart of the medical ablation catheter control  26 . The medical ablation catheter control  26  comprises a microcontroller  38  containing program and data memory  40  and digital inputs and outputs. The microcontroller  38  can be a Microchip PIC 16F877 and the like. The inputs  42  are coupled to the microcontroller  38  and configured for receiving position information of an ablation catheter  20  from an electronic position detection system  32 . More specifically, the inputs  42  can include a low battery detection signal, sensitivity control setting being such as allowed electrode movement boundaries and the like, and a serial data input reading X, Y, and Z electrode from the electronic position detection system. LocaLisa uses real-time 3-dimensional (3D) localization of intracardiac catheter electrodes as described in U.S. Pat. No. 5,983,126 “Catheter location system and method” by Wittkampf (9 Nov. 1999). This method uses an externally applied electrical field that is detected via standard catheter electrodes. Three skin-electrode pairs are used to send three small, 1.0 mA currents through the thorax in three orthogonal directions, with slightly different frequencies of 30 kHz used for each direction. The resulting voltage can be recorded via standard catheter electrodes and be used to determine electrode position. 
   The output  44  is coupled to the microcontroller  38  and configured for communicating ablation catheter  20  movement. The output  44  can include multiple outputs  44  such as an optical control block controlling the annunciating data signals, an RF source control block that terminates RF energy and the serial data output containing X, Y, Z electrode position information to the computer for graphical display of the electrode position. The medical ablation catheter control  26  includes software residing in program memory inside the microcontroller  38 . The software comprises an initialization program  46  for initializing microcontroller hardware, a movement program  48 , a comparison program  50 , and an annunciating program  52 . Some embodiments of the medical ablation catheter control  26  can include a control program  54 , a response program  56 , and a physiological movement program  58 . 
     FIG. 5  shows a flowchart of the movement program  48 . The movement program  48  resides in memory  40  and reads position information from the input  42  (also know as a serial interface) to calculate ablation catheter movement. In some embodiments, the movement program  48  can read two frames of electrode position information from the input  42 , validate this data, and store data into internal data memory  40 . The second frame of data is stored in a different location of memory  40  by incrementing a Random Access Memory (RAM) address pointer. At least two frames of electrode position information are stored, so the comparison program  50  can calculate a change in location (FIGS.  6 - 7 ). 
     FIGS. 6-7  show a flowchart of the comparison program  50 . The comparison program  50  resides in memory  40  and compares ablation catheter  20  movement to predetermined control data and calculates the difference between the electrode position data frames for X, Y and Z coordinates. The comparison program  50  decrements the address pointer to locate the position where the first frame is stored in RAM. The first frame X-axis data (X0) is read from RAM. The address pointer is incremented and the second frame X-axis data (X1) is read from RAM. The first frame X-axis data (X0) is subtracted from the second frame X-axis data (X1) to calculate X axis position change. The result of the subtraction can be zero, positive or negative. Out of the X-axis position change, velocity can be calculated along the X-axis. If the result of the subtraction is positive, the sensitivity setting, i.e. the allowed change of position selected by the operator, is subtracted [(X1−X0)−sensitivity setting]. If the result of the subtraction is negative, the sensitivity setting is subtracted from (X0−X1) to ensure that always a positive result from the subtraction of X0 and X1 is used for the subtraction with the sensitivity setting. The result of the subtraction with the sensitivity setting can be zero, i.e. the change in position along the X-axis is exactly that of the allowed limit, negative, i.e. the change in position is smaller than the allowed limit, or positive, i.e. the change in position is higher than the allowed limit (dislocation). The same routine and calculations are to be performed for the Y-axis and the Z-axis. Predetermined control data, as referred to the sensitivity settings, can be between 1.0 and 10.0 cm/sec and is typically the allowed limit for catheter electrode displacement. 
     FIG. 8  shows a flowchart of the annunciating program  52 . The annunciating program  52  resides in memory  40  and is coupled to the outputs of the comparison program. The annunciating program  52  indicates the relation of ablation catheter  20  movement to the predetermined control data and displays the catheter electrode velocity in mm/sec in X, Y and Z direction. The annunciating program  52  can also indicate predetermined messages such as “no movement”, “max. movement”, “movement within predetermined boundaries”, “movement exceeds predetermined boundaries”, “catheter dislocation”, and the like. 
     FIGS. 9-10  show a flowchart of the control program  54 . The control program  54  resides in memory  40  and reads user settings and predetermined control data. A predetermined movement range is set  57  in some embodiments using switches  34  that correspond to control parameters. A first time, a first x axis coordinate, a first y axis coordinate, and a first z axis coordinate are read  59 . At a second time, a second x axis coordinate, a second y axis coordinate, and a second z axis coordinate are read  60 . A difference is calculated  62  between the first x axis coordinate and the second x axis coordinate, the first y axis coordinate and the second y axis coordinate, and the first z axis coordinate and the second z axis coordinate. The difference is compared  64 with the predetermined movement range. A decision  66  is made concerning whether an ablation catheter  20  has exceeded the predetermined movement range. 
     FIG. 11  shows a flowchart of the response program  56 . The response program  56  resides in memory  40  and is coupled to one of the outputs of the comparison program. The response program  56  activates RF source control block and interrupts RF energy to the ablation catheter  20  when ablation catheter  20  movement exceeds the predetermined movement range. The response program  56  can interrupt power to the ablation catheter  20  in less than 500.0 ms after determining that movement has exceeded the predetermined value. In some versions, the response program  56  can interrupt power in as little as 1.0 ms. 
     FIG. 12  shows a flowchart of the physiological movement program  58 , and  FIG. 14  shows the physiological movement program  58  in relation to a method for ablation control. The physiological movement program  58  establishes a physiological movement baseline. The physiological movement baseline can be used to calculate respiratory rate and heart rate. The physiological movement program  58  comprises recording  68  physiological movement data and processing  70  physiological movement data. Physiological movement data is recorded over a period of time X coordinates, Y coordinates and Z coordinates while the ablation catheter position remains substantially unchanged. Physiological movement data is processed to determine a physiological movement baseline. Physiological movement boundaries are established  72  and can be used to adjust the predetermined movement control data. More specifically, the physiological movement program initiates the counter value, e.g. 150, meaning that 150 position data frames will be stored into memory. A first position data frame with X, Y, and Z position data will be read from the serial interface and stored into data memory. The counter is decremented by one and another data frame is read and stored. This will be repeated until the counter is zero (150 position data frames have been read and stored). Out of these position data frames, the minimal and maximal values for X, Y, Z position data are calculated. The maximal and minimal values can be used to calculate an adjusted sensitivity setting and to adjust the sensitivity parameters. The duration between 2 Maximal or Minimal values can be used to calculate and annunciate breathing rate. The duration between 2 local Maximal and Minimal values can be used to calculate and annunciate heart rate. 
     FIG. 13  shows a drawing of the change in electrode position along the axis due to physiological movement. The physiological movement is related to the beating of the heart and the breathing of the patient. The physiological movement program  58  establishes a physiological movement baseline during an unchanged catheter position. Out of these position data frames, the minimal and maximal values for X, Y, Z position data are calculated. These calculated values can be used to adjust the sensitivity parameters. The adjusted sensitivity can be calculated as: 
               Adjusted   ⁢           ⁢   Sensitive   ⁢           ⁢   Setting     =     SensitivitySetting   +     [       (     MaximalValue   -   MinimalValue       2     ]               Equation   ⁢           ⁢   1               
Other embodiments of the adjusted sensitive setting can be performed with other mathematical adjustments. The duration between 2 Maximal or Minimal values can be used to calculate breathing and annunciate breathing rate. The breathing rate per minute can be calculated as follows: 
               Breathing   ⁢           ⁢   Rate     =     60     Duration   ⁢           ⁢   Between   ⁢           ⁢   2   ⁢           ⁢     Maxima   /   Minima                 Equation   ⁢           ⁢   2               
Local Maximal and Minimal values, between 2 Maximal or 2 Minimal values (in seconds), can be determined and the duration between local maximal or 2 minimal values can be used to calculate and annunciate heart rate. The heart rate per minute can be calculated as follows: 
               Heart   ⁢           ⁢   Rate     =       60   ,   000       Duration   ⁢           ⁢   Between   ⁢           ⁢   Local   ⁢           ⁢     Maxima   /   Minima                 Equation   ⁢           ⁢   3               
     FIG. 14  shows a flowchart of a method for ablation catheter control  26 . The method begins with positioning an ablation catheter  20 . The distal position of the ablation catheter is monitored  74  with an electronic position detection system that generates position information. Position information is processed  76  to calculate ablation catheter movement. Ablation catheter movement is compared  78  to predetermined control data. The relation of ablation catheter movement to the predetermined control data is annunciated  80 . Some embodiments of the method can also include the following elements. Once ablation catheter movement is compared to predetermined control data, a determination  82  can also be made of whether ablation catheter movement exceeds a predetermined movement range. Power to the ablation catheter can be interrupted  84  when movement exceeds the predetermined movement range. Physiological movement data can be recorded over a period of time x coordinates, y coordinates and z coordinates while the ablation catheter position remains substantially unchanged. Physiological movement data can be processed to determine a physiological movement baseline. Physiological movement boundaries can be established  72  according to the physiological movement baseline. 
     FIG. 15  shows the experimental tank setup. The tank was filled with saline solution simulating the patient. Distance markers on the catheter  20  shaft were used for different speeds of electrode movement by manually dragging for a certain time along the appropriate distance. LocaLisa electrodes providing the excitation current.  FIG. 16  shows an operational flowchart of the medical ablation catheter control as used in the preliminary experiments with a first prototype. 
   An embodiment of the invention was developed and tested that initiates termination of RF delivery automatically upon catheter dislocation. The embodiment consisted of a microprocessor connected between the indifferent cable of the RF generator and the indifferent electrode (FIG.  2 ). The software program was developed using Microchip-MPLAB. This software inside the microprocessor continuously evaluates the X, Y and Z position information collected from the LocaLisa system that is transmitted at 9600 bits per second and updated ten times per second thus a change in electrode position can be detected within 200 ms. Four different sensitivity levels were programmed, i.e. 10, 20, 50 and 100. A sensitivity level of 10 allows a change in electrode position in either X, Y and Z direction of +/−10 mV without interaction by the embodiment of the invention. A red light indicates a sudden change within 200 ms of greater than the selected sensitivity level and an electronic switch is activated by the software to interrupt the connection between the indifferent electrode and the RF generator resulting in a high impedance shutdown and termination of RF energy delivery. Assuming a field strength of 50 mV/cm, the sensitivity values correspond to an electrode movement of 0.2 cm, 0.4 cm, 1 cm and 2 cm, respectively. This translates into speeds of electrode movement of 1 cm/sec, 2 cm/sec, 5 cm/sec and 10 cm/sec, respectively, considering the duration of 200 ms in which this movement must occur in order to initiate termination of RF energy.The RF safety device was connected according to FIG.  2  and tested in an in vitro tank simulating the patient. The LocaLisa electrodes, applying the 1.0 mA current, were connected at the tank having a connection to the inner of the tank that was filled with isotonic saline solution. The ablation catheter (RF Marinr, Medtronic EPSystems) was positioned inside the tank and connected to the RF generator (Atakr II, Medtronic EPSystems). During a constant RF power delivery of 25 W the catheter was manually withdrawn with a dragging speed of either 0.5, 1, 2, 5, 10, 15 or 20 cm/sec. and the reaction of the RF safety device was documented. Distance markers on the catheter shaft were used for different speeds of electrode movement by manually dragging for 1 second along the appropriate distance. 
   Every setting was repeated three times. For the sensitivity levels 10, 20, 50 and 100, an immediate termination of RF delivery was observed for an electrode dragging speed of greater or equal than 1 cm/sec, 2 cm/sec, 5 cm/sec and 10 cm/sec, respectively. The termination of RF delivery was achieved by an automatic shutdown of the generator due to an impedance of greater than 250Ω. 
   Embodiments of the medical ablation control catheter are disclosed. One skilled in the art will appreciate that the present invention can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation, and the present invention is limited only by the claims that follow.