Abstract:
A medical device is provided, including an ablation system with a generator, at least one ablation element, a patient return electrode, and a feedback system to verify and monitor the electrical connection between the generator and the patient return electrode, as well as contact of the patient return electrode with the patient. If an electrical connection is absent, intermittent, or of low quality, the medical device may also provide notice, a warning or alarm, and may also automatically cease ablation occurring at that time.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    N/A. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    N/A. 
       FIELD OF THE INVENTION 
       [0003]    The present invention relates generally to medical systems and methods of use thereof, and more particularly to an ablation system for detecting and monitoring a patient return electrode. 
       BACKGROUND OF THE INVENTION 
       [0004]    Numerous procedures involving catheters and other minimally invasive devices may be performed for a wide variety of treatments, such as ablation, angioplasty, dilation or other similar therapies. For example, there are many variations of cardiac arrhythmias with different causes, including atrial fibrillation, generally involving irregularities in the transmission of electrical impulses through the heart. To treat cardiac arrhythmias or irregular heartbeats, physicians often employ specialized ablation catheters to gain access to interior regions of a patient&#39;s body. Such catheters include tip electrodes or other ablating elements to create ablation lesions that physiologically alter the ablated tissue without removal thereof, disrupting or blocking electrical pathways through the targeted tissue. In the treatment of cardiac arrhythmias, a specific area of cardiac tissue, such as for example atrial rotors, having aberrant electrically conductive pathways with erratic electrical impulses is initially localized. A medical practitioner (such as a physician) may direct a catheter through a body passage including for example a blood vessel into the interior region of the heart that is to be treated. Subsequently, the ablating portion of the selected device is placed near the targeted cardiac tissue to be ablated, such as for example a pulmonary vein ostium or atrium. 
         [0005]    An ablation procedure may involve creating one or more lesions in order to electrically isolate tissue believed to be the source of an arrhythmia. During the course of such a procedure, a physician may perform, for example, radio-frequency (RF) ablation with an RF generator and a medical device such as a catheter having at least one ablation electrode. RF ablation systems may have one or more modes of operation, including for example: (i) bipolar ablation between at least two electrodes on an ablation device within a patient&#39;s body, (ii) monopolar ablation between an electrode on an ablation device within a patient&#39;s body and an external electrode contacting a patient&#39;s skin, and (iii) a combination of the monopolar and bipolar modes. The external electrode may have the form of one or more adhesive patches, which may be attached to the patient&#39;s back, and may be called a “patient return electrode.” 
         [0006]    For acceptable performance and operation in the monopolar mode or in any combination monopolar and bipolar mode, the patient return electrode should have good contact with the patient, and a continuous electrical connection to the RF generator. Accordingly, it is desirable to provide a medical device able to verify and monitor the electrical connection between an RF generator and a patient return electrode, as well as sufficient contact between a patient return electrode and the patient. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention advantageously provides a medical system for treating patients with tissue ablation, including a generator, a catheter with at least one ablation element, a patient return electrode, and a feedback system to verify and monitor the electrical connection between the generator and the patient return electrode, as well as contact of the patient return electrode with the patient. 
         [0008]    In particular, a medical system is provided, including a catheter having an ablation element, a radiofrequency generator connected to the catheter, the generator being operable to deliver monopolar ablation energy to the ablation element, a patient return electrode connected to the generator, and a feedback system connected to the generator and the patient return electrode, the feedback system operating to continuously monitor energy in the patient return electrode, and to cease delivery of ablation energy when the patient return electrode energy is less than a preselected threshold. 
         [0009]    A medical system is also provided, including a catheter having an ablation element, a generator connected to the catheter, the generator being operable to deliver monopolar ablation energy to the ablation element, a patient return electrode connected to the generator, a resistor connected to the patient return electrode and defining a voltage, a convertor connected to the resistor and having an output generating a signal corresponding to the voltage, and a processor connected to the generator and the output, operable to continuously monitor the signal and cease delivery of ablation energy when the signal is less than a preselected threshold. 
         [0010]    A method of treating a patient is provided, including providing an ablation system having an ablation element and a patient return electrode, defining a threshold, placing the ablation element proximate to a treatment site, placing the patient return electrode in contact with the patient, delivering ablation energy to the ablation element, measuring energy in the patient return electrode, comparing the measured energy to the threshold, and if the measured energy is less than the threshold, generating an alert and ceasing the delivery of ablation energy. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, wherein: 
           [0012]      FIG. 1  is an illustration of a medical system in accordance with the principles of the present invention; 
           [0013]      FIG. 2  is an illustration of an electrical device of the medical system of  FIG. 1 , in accordance with the principles of the present invention; 
           [0014]      FIG. 3  is an illustration of an electrical device having additional components in accordance with the principles of the present invention; 
           [0015]      FIG. 4  is an illustration of a medical device in accordance with the principles of the present invention; 
           [0016]      FIG. 5  is an illustration of an additional medical device in accordance with the principles of the present invention; 
           [0017]      FIG. 6  is a perspective illustration of a treatment assembly for the medical device of  FIG. 5 , in accordance with the principles of the present invention; 
           [0018]      FIG. 7  is an illustration of the treatment assembly of  FIG. 6 , in accordance with the principles of the present invention; 
           [0019]      FIG. 8  is an illustration of another treatment assembly in accordance with the principles of the present invention; 
           [0020]      FIG. 9  is an illustration of an additional treatment assembly in accordance with the principles of the present invention; 
           [0021]      FIG. 10  is an illustration of a medical system having an additional patient return electrode, in accordance with the principles of the present invention; 
           [0022]      FIG. 11  is an illustration of a medical system in accordance with the principles of the present invention, showing partial anatomical reference of a patient&#39;s heart; and 
           [0023]      FIG. 12  is an illustration of a flow diagram in accordance with the principles of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    The present invention advantageously provides a medical system and method for treating patients by performing an ablation procedure in which electrical connections between portions of the medical system and the patient are verified and monitored, thereby enhancing the safety and efficacy of the therapeutic procedure. In particular and as shown in  FIG. 1 , an ablation therapy system, generally designated at  10 , is provided for treating unwanted tissue conditions, including for example atrial fibrillation or other arrhythmias. The ablation therapy system  10  may generally include an electrical generator such as for example a radio-frequency (“RF”) generator  12 , an electrocardiogram (“ECG”) interface unit  14  operably coupled to the RF generator  12 , and a medical device  16 . 
         [0025]    The medical device  16  may include a catheter for performing various medical treatments, including for example an electrophysiology catheter which may be operably coupled to the RF generator  12  and the ECG interface unit  14 . The medical device  16  may have a shape and dimensions to reach various treatments sites, such as intraluminal access to vascular anatomy, including for example transseptal access to the left atrium of a patient&#39;s heart for subsequent treatment or ablation. The medical device  16  may generally define an elongated, flexible catheter body  18  having a distal treatment assembly  20 , as well as a handle assembly  22  at or near a proximal end of the catheter body  18 . 
         [0026]    The distal treatment assembly  20  may, for example, include one or more ablation elements such as electrodes  24 , each of which may be electrically coupled to the RF signal generator  12 . A patient return electrode  26  may also be provided, and may include a conductive pad having a greater surface area than the electrodes  24 . The patient return electrode  26  may be external to the patient, for example in contact with the patient&#39;s skin through an adhesive attachment to the back of the patient, and may be operably coupled to the ECG interface unit  14  and/or directly to the RF generator  12 . 
         [0027]    The ablation therapy system  10  may have one or more modes of operation, including for example: (i) bipolar ablation between at least two of the electrodes  24  on the medical device  16  within a patient&#39;s body, (ii) monopolar ablation between one of the electrodes  24  on the medical device  16  within a patient&#39;s body and the patient return electrode  26  contacting a patient&#39;s skin, and (iii) a combination of the monopolar and bipolar modes. 
         [0028]    In other words, the RF generator  12  may be operable (i) to deliver ablation energy to the electrodes of the treatment assembly in a bipolar mode, directing energy between pairs of the electrodes  24  on the medical device  16 , and (ii) to deliver ablation energy to one electrode  24  of the distal treatment assembly  20  and through the patient return electrode  26  in a monopolar mode. The RF generator  12  may also be operable to deliver ablation energy in a combination of the monopolar mode and the bipolar mode. 
         [0029]    The RF generator  12  may also include a user interface  28  which may include a display and/or a remote control  30 , which enable a user to select parameters for desired mapping and/or ablation treatment. The user interface  28  may allow the user to select an energy delivery mode for treatment, such as for example, selection among the delivery of only monopolar energy, only bipolar energy, or a combination of the two. When in combination mode, the user interface  28  may also allow selection a power ratio of monopolar energy to bipolar energy, such as 1:1, 2:1, or 4:1. The RF generator  12  may offer a set of specific energy ratios by default, such that the user can select one of the established energy ratios, and/or the user interface can allow the user to enter a different custom energy ratio. The user interface  28  may also allow changing the energy mode when the catheter is changed, or when the medical device  16  is moved to a different location to ablate different tissue. 
         [0030]    The ECG interface unit  14  may also have an ECG monitoring unit or display  32  to monitor and map signals detected by the electrodes  24  of the distal treatment assembly  20  of the medical device  16 . The RF generator  12  and the ECG interface unit  14  may both be operably coupled to the medical device  16 . The ECG interface unit  14  may be designed to electrically isolate itself and the display  32  from the signals generated by the RF generator  12 , which may include isolation from large magnitude signals and electrical noise that may result from the RF generator  12 . 
         [0031]    A feedback system  34  may be operably coupled with the RF generator  12  and the patient return electrode  26  to continuously monitor energy in the patient return electrode  26 , and to cease delivery of ablation energy from the RF generator  12  if energy in the patient return electrode  26  falls below a preselected threshold. During delivery of monopolar ablation energy between one or more ablation electrodes  24  and the patient return electrode  26 , in the monopolar mode or any combination mode, it is desirable to maintain good electrical contact between the RF generator  12  and the patient return electrode  26 , and likewise between the patient return electrode  26  and the patient. 
         [0032]    Referring to  FIG. 2 , the RF generator  12  may also have a processor  36  with a plurality of ablation outputs  38  coupled with an ablation connector  74 . The feedback system  34  may be positioned within an enclosure of the RF generator  12  and coupled with a patient return electrode connector  76 . In the generator shown in  FIG. 2 , the feedback system  34  is coupled in parallel with the patient return electrode  26 , and may include a resistor  40 , a transformer  42 , and a convertor  44  operable to continuously monitor voltage across the resistor  40  and produce an output feedback signal at a convertor output  46 . The resistor  40  may have a relatively small resistance, on the order of for example 0.1 ohms. The transformer  42  may be connected between the resistor  40  and the convertor  44 , and may have a 1:1 input to output characteristic, to isolate the circuits on either side of the transformer  42 . 
         [0033]      FIG. 3  depicts a more specific example of an RF generator having a more detailed feedback system. The processor  36 , ablation outputs  38 , resistor  40 , transformer  42 , ablation connector  74  and patient return electrode connector  76  are the same as those in  FIG. 2 . A convertor  48  is a root-mean-square (“RMS”) to direct-current (“DC”) convertor, which incorporates an integrated circuit  50  such as for example the commercially available integrated circuit convertor LTC 1968, with several components such as for example resistors  78  and capacitors  80 , to produce a DC output feedback signal at a convertor output  52 . 
         [0034]    During delivery of ablation energy, the ablation therapy system  10  determines an acceptable threshold or range of an output of the feedback system  34 . When the measured output is outside that acceptable threshold or range, then the ablation therapy system  10  stops ablating and may generate an alert or indication. 
         [0035]    For example, the feedback system  34  determines a measured parameter such as a voltage at the convertor output  46  or  52 . The processor  36  is operable to calculate a preselected threshold and compare it to the measured parameter. If the measured parameter at the convertor output  46  is greater than the preselected threshold, then ablation may continue as under normal operating conditions to treat the patient. If the measured parameter at the convertor output  46  is less than the preselected threshold, the feedback system  34  is operable to cease delivery of ablation energy, and may cause an alarm or warning. 
         [0036]    The processor  36  may be programmed to calculate an expected feedback parameter, which may vary depending on the current mode of operation, and then compare the measured parameter to the expected parameter. The processor may further be programmed to calculate a ratio of the measured parameter divided by the expected parameter, and compare it to a preselected threshold. For example, the preselected threshold may be selected at any suitable amount, ranging from 100% to a small percentage. In one particular example, the threshold may be selected to equal approximately 25%. 
         [0037]    As a specific example, the threshold value may vary according to the current mode of operation, along the lines of the following table: 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 DC output 
                 DC output 
               
               
                   
                 Mode 
                 All channels on 
                 Any one channel on 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Monopolar (1:0) 
                 0.25 
                 0.044 
               
               
                   
                 Combination (1:1) 
                 0.16 
                 0.033 
               
               
                   
                 Combination (2:1) 
                 0.1 
                 0.025 
               
               
                   
                 Combination (4:1) 
                 0.03 
                 0.006 
               
               
                   
                   
               
             
          
         
       
     
         [0038]    When the ratio of the measured parameter divided by the expected parameter is less than the threshold value, the processor may be programmed to provide an alarm and switch off the ablation energy. The alarm or warning may be auditory, visual, or tactile. After the practitioner verifies proper setup and operation of the system, an override switch (not shown) may be provided to manually reset the ablation therapy system and resume treatment of the patient. 
         [0039]    Now referring to  FIGS. 4-9 , some exemplary medical devices are depicted. In particular,  FIG. 4  shows an ablation catheter  54  having a distal treatment assembly  56  in which the electrodes have a linear configuration. The distal treatment assembly  56  may be used for bipolar ablation between the electrodes of the distal treatment assembly  56 , or for monopolar ablation between one electrode and a patient return electrode  26 , or a combination of bipolar ablation and monopolar ablation. A proximal handle  82  has a rotational actuator  84  for manipulating, bending, steering and/or reshaping the distal treatment assembly  56  into various desired shapes, curves, etc. 
         [0040]      FIGS. 5-7  show an ablation catheter  58  with a distal treatment assembly  60  in which the electrodes have a planar configuration. Similar to the ablation catheter  54 , the distal treatment assembly  58  may be used for bipolar ablation, monopolar ablation, or a combination thereof. A proximal handle  86  has a rotational actuator  88  for manipulating a distal portion of the ablation catheter  58 , and a linear actuator  90 . The linear actuator  90  can advance the distal treatment assembly  60  distally beyond a catheter shaft, and retract the distal treatment assembly  60  proximally inside the catheter shaft. When the distal treatment assembly  60  is advanced distally, it may resiliently expand from a compressed arrangement inside the catheter shaft to the deployed arrangement shown in  FIGS. 6 and 7 . 
         [0041]      FIG. 8  shows a catheter  62  which has a distal treatment assembly  64  having a resilient framework in which the electrodes have a proximally-directed configuration, which may for example be used for transseptal treatments of a patient&#39;s heart. 
         [0042]      FIG. 9  shows a catheter  66  which has a distal treatment assembly  68  in which the electrodes have an adjustable linear, planar, or spiral configuration. 
         [0043]    Now referring to  FIG. 10 , an ablation treatment system  70  may also a plurality of patient return electrodes  72 , with a processor operable to independently monitor electrical energy in each patient return electrode  72 . The processor may also operate to calculate a combined expected feedback parameter from both patient return electrodes  72 , determine a combined measured parameter for both patient return electrodes  72 , calculate a ratio of the combined measured parameter divided by the combined expected parameter, and compare the ratio to a preselected threshold. 
         [0044]    Accordingly, the medical device  16  may be used to investigate and treat aberrant electrical impulses or signals in a selected tissue region, such as in the heart. Primarily, the distal treatment assembly  20  may be advanced through the patient&#39;s vasculature via the femoral artery over a previously inserted guidewire. The distal treatment assembly  20  may then be advanced into the right atrium and into proximity of a pulmonary vein, for example. 
         [0045]    In an exemplary use of the present system as illustrated in the flow diagram of  FIG. 12 , the medical system is first prepared for ablation, and the ablation system is set up (step  100 ). One or more patient return electrodes are placed (step  102 ), and the ablation catheter is placed so that the distal treatment assembly  20  is in the desired position for treatment (step  104 ). Various ablation parameters are determined, including the intended duration of ablation (step  106 ). The desired ablation mode is selected, for example monopolar ablation, bipolar ablation, or a specific combination thereof, and the expected feedback is determined (step  108 ). A threshold value is calculated based on the selected parameters and mode of ablation (step  110 ), which may be a preselected percentage of the expected feedback. If all parameters are not acceptable (step  112 ), then the setup and parameters are evaluated and corrected (step  124 ). If all parameters are acceptable (step  112 ), then delivery of ablation energy may commence (step  114 ). 
         [0046]    During ablation, the feedback signal or output is continuously verified and monitored (step  116 ). A ratio of the measured feedback divided by the expected feedback is calculated (step  118 ). If the feedback ratio is greater than the threshold value (step  120 ), then all parameters continue to be evaluated (step  112 ), and ablation continues as under normal conditions until a parameter is not acceptable or the intended ablation duration completes. If the feedback ratio is equal to or less than the threshold value (step  120 ), then ablation stops, and the system indicates a warning (step  122 ). 
         [0047]    Sufficient contact with tissue may be determined through fluoroscopic imaging. In addition, the location and tissue contact can be confirmed using the electrodes  24  of the medical device. For example, an electrophysiologist can map the contacted tissue to not only determine whether or not to ablate any tissue, but to also confirm tissue contact which is identified in the mapping procedure. If conditions are determined to be inadequate, an operator may adjust the shape of carrier assembly, and/or the operator may reposition the distal treatment assembly  20  against tissue through various manipulations performed at the proximal end of the medical device  16 . Moreover, it will be appreciated that other conventional mapping catheters can be applied to map signals, such as a standard electrophysiology lasso catheter. 
         [0048]    Once sufficient tissue contact has been established and the mapping procedure has confirmed the presence of aberrant conductive pathways, ablation energy may be passed through the electrodes  24  (for example, 5-10 Watts) of the distal treatment assembly  20 . The distal treatment assembly  20  and the RF signal generator  12  may cooperate to deliver RF energy in monopolar, bipolar or combination monopolar-bipolar energy delivery modes, simultaneously or sequentially, and with or without durations of terminated energy delivery. 
         [0049]    While examples and illustrations of particular medical system configurations have been provided, it is understood that various arrangements, shapes, configurations, and/or dimensions may be included in the medical device of the present invention, including but not limited to those illustrated and described herein. Also, though monopolar and bipolar RF ablation energy may be the selected forms of energy to pass through the electrodes of the medical device, other forms of ablation energy may be additionally or alternatively emitted from the treatment assembly, including electrical energy, magnetic energy, microwave energy, thermal energy (including heat and cryogenic energy) and combinations thereof. Moreover, other forms of energy that may be applied can include acoustic energy, sound energy, chemical energy, photonic energy, mechanical energy, physical energy, radiation energy and a combination thereof. 
         [0050]    It should be understood that an unlimited number of configurations for the present invention could be realized. The foregoing discussion describes merely exemplary embodiments illustrating the principles of the present invention, the scope of which is recited in the following claims. In addition, unless otherwise stated, all of the accompanying drawings are not to scale. Those skilled in the art will readily recognize from the description, claims, and drawings that numerous changes and modifications can be made without departing from the spirit and scope of the invention.