Abstract:
Provided are a method and apparatus for performing medical catheterization using electrical power circuitry disposed outside a medical catheter and remote internal circuitry disposed within the medical catheter. At least one of the power circuitry and the internal circuitry is isolated from electrical ground. Exactly two wires connect the power circuitry to the internal circuitry and a signal generator is provided for generating an alternating carrier that is communicated from the power circuitry to the internal circuitry via the wires. Decoders are disposed in the power circuitry and the internal circuitry, and a transceiver performs half-duplex data communication between the power circuitry and the internal circuitry by alternately modulating the carrier voltage amplitude in one of the power circuitry and the internal circuitry and decoding the modulated carrier voltage amplitude in another of the power circuitry and the internal circuitry.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application claims the benefit of U.S. Provisional Application No. 62/259,370, filed 24 Nov. 2015, which is herein incorporated by reference. 
     
    
     COPYRIGHT NOTICE 
       [0002]    A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 
       FIELD 
       [0003]    The presently described subject matter relates to transferring non-mechanical forms of energy to or from the body. More particularly, the described subject matter relates to transferring radiofrequency energy into the heart for ablation. 
       BACKGROUND 
       [0004]    Mapping of electrical potentials in the heart is now commonly performed, using cardiac catheters comprising electrophysiological sensors for mapping the electrical activity of the heart. Typically, time-varying electrical potentials in the endocardium are sensed and recorded as a function of position inside the heart, and then used to map a local electrogram or local activation time. 
         [0005]    When conduction abnormalities, such as atrial fibrillation are present, radiofrequency (RF) ablation of the heart is a procedure that is widely used to correct problematic cardiac conditions. The procedure typically involves insertion of a catheter having an electrode into the heart, and ablating selected regions within the heart with RF energy transmitted via the electrode. 
       SUMMARY 
       [0006]    Safety requirements can be limiting factors in miniaturization of devices for intra-body applications. For example, catheters used for electrophysiological procedures have various sensors in their distal portions, while processing of the signals from the sensors can occurs proximally. However, providing signal processing capabilities in the distal portion of the catheter can improve the quality of the electrophysiological data and measurements. Signal processing circuitry requires electrical power to be supplied to the distal portion of the catheter. If mechanical failure of the catheter shaft or a short circuit in the power wires supplying the signal processing circuitry were to occur, the subject could experience an electrical shock. The presently described subject matter is directed to methods and systems that provide electrical safety in devices for intra-body applications. 
         [0007]    The presently described subject matter is directed to a method, comprising disposing electrical power circuitry outside a medical catheter; disposing remote internal circuitry within the medical catheter; isolating at least one of the power circuitry and the internal circuitry from electrical ground; connecting the power circuitry to the internal circuitry by two wires, for example, by exactly two wires; and communicating an alternating carrier from the power circuitry to the internal circuitry via the two wires. The method may further comprise performing half-duplex data communication between the power circuitry and the internal circuitry by, for example, alternately modulating the carrier voltage amplitude with one of the power circuitry and the internal circuitry and decoding the modulated carrier voltage amplitude with another of the power circuitry and the internal circuitry. 
         [0008]    According to one aspect of the presently described method, the power circuitry can comprise a transceiver for modulating the carrier voltage amplitude and a decoder for demodulating the carrier voltage amplitude. 
         [0009]    According to a further aspect of the presently described method, the internal circuitry can comprise a decoder for demodulating the carrier voltage amplitude. 
         [0010]    Yet another aspect of the method can comprise obtaining and processing data in the internal circuitry from sensors in the catheter and modulating the carrier voltage amplitude according to the processed data for communication a decoder to the power circuitry. 
         [0011]    According to still another aspect of the method alternately modulating the carrier voltage amplitude is performed with a first switch in the power circuitry and with a second switch in the internal circuitry to vary first and second resistances across the alternating carrier, respectively. 
         [0012]    According to certain embodiments of the presently described subject matter an apparatus, further provided is an apparatus comprising a medical catheter; electrical power circuitry disposed outside the catheter; and remote internal circuitry disposed within the catheter. At least one of the power circuitry and the internal circuitry is isolated from electrical ground. The apparatus may further include two wires, for example, exactly two wires, connecting the power circuitry to the internal circuitry, and a signal generator for generating an alternating carrier that is communicated from the power circuitry to the internal circuitry via the wires. Decoders are disposed in the power circuitry and the internal circuitry, and a transceiver performs half-duplex data communication between the power circuitry and the internal circuitry. The transceiver is operative for alternately modulating the carrier voltage amplitude in one of the power circuitry and the internal circuitry and decoding the modulated carrier voltage amplitude in the decoder of another of the power circuitry and the internal circuitry. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0013]    For a better understanding of the presently described subject matter, reference is made to the detailed description of the presently described subject matter, by way of example, which is to be read in conjunction with the following drawings, wherein like elements are given like reference numerals, and wherein: 
           [0014]      FIG. 1  is a pictorial illustration of a system, which is constructed and operative in accordance with a disclosed embodiment of the presently described subject matter; 
           [0015]      FIG. 2  is an electrical schematic of an embodiment of a system for digital communication in accordance with an embodiment of the presently described subject matter; and 
           [0016]      FIG. 3  is a flow chart illustrating a sequence of operations using the system shown in  FIG. 2  in accordance with an embodiment of the presently described subject matter. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    In the following description, numerous specific details are set forth in order to provide a thorough understanding of the various principles of the presently described subject matter. It will be apparent to one skilled in the art, however, that not all these details are necessarily needed for practicing the presently described subject matter. In this instance, well-known circuits, control logic, and the details of computer program instructions for conventional algorithms and processes have not been shown in detail in order not to obscure the general concepts unnecessarily. 
         [0018]    Documents incorporated by reference herein are to be considered an integral part of the application except that, to the extent that any terms are defined in these incorporated documents in a manner that conflicts with definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered. 
       Overview 
       [0019]    Turning now to the drawings, reference is initially made to  FIG. 1 , which is a pictorial illustration of a system  10  for evaluating electrical activity and performing ablative procedures on a heart  12  of a living subject, which is constructed and operative in accordance with a disclosed embodiment of the presently described subject matter. The system comprises a catheter  14 , which is percutaneously inserted by an operator  16  through the patient&#39;s vascular system into a chamber or vascular structure of the heart  12 . The operator  16 , who is typically a physician, brings the catheter&#39;s distal tip  18  into contact with the heart wall, for example, at an ablation target site. Electrical activation maps may be prepared, according to the methods disclosed in U.S. Pat. Nos. 6,226,542, and 6,301,496, and in commonly assigned U.S. Pat. No. 6,892,091, whose disclosures are herein incorporated by reference. One commercial product embodying elements of the system  10  is available as the CARTO® 3 System, available from Biosense Webster, Inc., 3333 Diamond Canyon Road, Diamond Bar, Calif. 91765. This system may be modified by those skilled in the art to embody the principles of the presently described subject matter. 
         [0020]    Areas determined to be abnormal, for example by evaluation of the electrical activation maps, can be ablated by application of thermal energy, e.g., by passage of radiofrequency electrical current through wires in the catheter to one or more electrodes at the distal tip  18 , which apply the radiofrequency energy to the myocardium. The energy is absorbed in the tissue, heating it to a point (typically about 50° C.) at which it permanently loses its electrical excitability. When successful, this procedure creates non-conducting lesions in the cardiac tissue, which disrupt the abnormal electrical pathway causing the arrhythmia The principles of the presently described subject matter can be applied to different heart chambers to diagnose and treat many different cardiac arrhythmias. 
         [0021]    The catheter  14  can comprise a handle  20 , having suitable controls on the handle to enable the operator  16  to steer, position and orient the distal end of the catheter as desired for the ablation. To aid the operator  16 , the distal portion of the catheter  14  contains position sensors (not shown) that provide signals to a processor  22 , located in a console  24 . The processor  22  may fulfill several processing functions as described below. 
         [0022]    Ablation energy and electrical signals can be conveyed to and from the heart  12  through one or more ablation electrodes  32  located at or near the distal tip  18  via cable  34  to the console  24 . Pacing signals and other control signals may be conveyed from the console  24  through the cable  34  and the electrodes  32  to the heart  12 . Sensing electrodes  33 , also connected to the console  24  are disposed between the ablation electrodes  32  and have connections to the cable  34 . 
         [0023]    Wire connections  35  link the console  24  with body surface electrodes  30  and other components of a positioning sub-system for measuring location and orientation coordinates of the catheter  14 . The processor  22  or another processor (not shown) may be an element of the positioning subsystem. The electrodes  32  and the body surface electrodes  30  may be used to measure tissue impedance at the ablation site as taught in U.S. Pat. No. 7,536,218, issued to Govari et al., which is herein incorporated by reference. A temperature sensor (not shown), including for example, a thermocouple or thermistor, may be mounted on or near each of the electrodes  32 . 
         [0024]    The console  24  may contain one or more ablation power generators  25 . The catheter  14  may be configured to conduct ablative energy to the heart using any known ablation technique, including for example, but not limited to, radiofrequency energy, ultrasound energy, and laser-produced light energy. Such methods are disclosed in commonly assigned U.S. Pat. Nos. 6,814,733, 6,997,924, and 7,156,816, both of which are herein incorporated by reference. 
         [0025]    In one embodiment, the positioning subsystem can comprise a magnetic position tracking arrangement that determines the position and orientation of the catheter  14  by generating magnetic fields in a predefined working volume and sensing these fields at the catheter, using field generating coils  28 . The positioning subsystem is described in U.S. Pat. No. 7,756,576, which is hereby incorporated by reference, and in the above-noted U.S. Pat. No. 7,536,218. 
         [0026]    As noted above, the catheter  14  is coupled to the console  24 , which enables the operator  16  to observe and regulate the functions of the catheter  14 . Console  24  includes a processor, preferably a computer with appropriate signal processing circuits. The processor is coupled to drive a monitor  29 . The signal processing circuits typically receive, amplify, filter, and digitize signals from the catheter  14 , including, for example, signals generated by sensors, including but not limited to, electrical, temperature, and contact force sensors, and a plurality of location sensing electrodes (not shown) located distally in the catheter  14 . The digitized signals are received and used by the console  24  and the positioning system to compute the position and orientation of the catheter  14 , and to analyze the electrical signals from the electrodes. 
         [0027]     Typically, the system  10  includes other elements, which are not shown in the figures for the sake of simplicity. For example, the system  10  may include an electrocardiogram (ECG) monitor, coupled to receive signals from one or more body surface electrodes, in order to provide an ECG synchronization signal to the console  24 . As mentioned above, the system  10  may also include a reference position sensor, either on an externally-applied reference patch attached to the exterior of the subject&#39;s body, or on an internally-placed catheter, which is inserted into the heart  12  maintained in a fixed position relative to the heart  12 . Conventional pumps and lines for circulating liquids through the catheter  14  for cooling the ablation site can be provided. The system  10  may receive image data from an external imaging modality, such as an MRI unit or the like and includes image processors that can be incorporated in or invoked by the processor  22  for generating and displaying images. 
         [0028]    Reference is now made to  FIG. 2 , which is an electrical schematic of an embodiment of a system for digital communication in a catheter using two alternating current (AC) coupling wires in accordance with an embodiment of the presently described subject matter. The components shown are dimensioned to an intra-body catheter. 
         [0029]    A system  40  comprises electrical power circuitry  42 , which is can be located outside the catheter, for example, in the console  24  ( FIG. 1 ). Power circuitry  42  comprises an alternating current signal generator  44  connected in a power supply circuit  46 . The signal generator  44  generates a carrier frequency in the range of tens or hundreds of kHz. The AC current passes through a network comprising resistors R 1 , R 2  and capacitors C 1 , C 2 . The AC current is used both as an electrical energy source for remote circuitry  48  and as the carrier frequency for information transfer between the power circuitry  42  and remote circuitry  48 . 
         [0030]    Power circuitry  42  includes a signal processing module  50 , which controls a switch  52  (ON/OFF) to modulate the carrier frequency. The signal processing module  50  includes an amplifier  54  and a transceiver  56 . The amplifier  54  receives and decodes or demodulates signals that are received from internal remote circuitry  48 . The transceiver  56  handles communications that are directed to the remote circuitry  48 . 
         [0031]    The remote circuitry  48  comprises an energy harvesting component  58 , a measurement and processing component  60  and an amplifier and decoder  62  for demodulating the carrier voltage amplitude. The energy harvesting component  58 , which can be model LTC3331 from Linear Technology, converts the AC voltage at its input to a DC voltage and charges the storage capacitor C 5  to a constant value that can be in the range of 3 to 10 volts direct current (VDC). The measurement and processing component  60  and amplifier and decoder  62  are switched in when the DC voltage on the capacitor C 5  reaches a predetermined value by switch  64 . 
         [0032]    As noted above, the remote circuitry  48  is remote from the power circuitry  42 . The power circuitry  42  and the remote circuitry  48  are connected by a wire pair  66 . The wire pair  66  may be implemented by a twisted pair that reduces sensitivity to external magnetic fields. 
       Operation 
       [0033]    An AC carrier current produced by signal generator  44  passes through resisters R 3 , R 4  and capacitors C 3 , C 4  in the power circuitry  42 ; then through wire pair  66  into the remote circuitry  48 . Data communication between the power circuitry  42  and remote circuitry  48  is implemented by carrier voltage amplitude modulation. The signal generator  44  together with the resistors R 1  and R 2  act as the current source and the voltage across the wires of the wire pair  66  depends on the impedance across the two wires. 
         [0034]    When both switches  52 ,  64  are open, i.e., in an OFF state, and the impedance of the capacitors C 1  and C 2  at the carrier frequency is much less than the values of R 1  and R 2 , the transmission (Tx) voltage between the wires assumes a first value: 
         [0000]        Tx=V 1*[ Rc /( R 1+ R 2+ Rc )], 
         [0000]    where V 1  is the output voltage of the signal generator  44  and Rc is the impedance of the parasitic capacitance and the load of the remote circuitry  48  at the carrier frequency. 
         [0035]    As noted above, the signal processing module  50  modulates the carrier voltage amplitude by varying switch  52  between open and closed positions. Signal processing module  50  influences only switch  52  and the remote circuitry  48  influences switch  64 . When switch  52  is closed and switch  64  is open, the Tx voltage between across the wire pair  66  assumes a second value: 
         [0000]        Tx=V 1*( Rc/R 1+ R 2+ Rc+R 6. 
         [0036]    When switch  52  is opened and switch  64  is closed the Tx voltage between across the wire pair  66  assumes a third value: 
         [0000]        Tx=V 1*( Rc/R 1+ R 2+ Rc+R 5). 
         [0037]    The amplifier and decoder  62  in the remote circuitry  48  receives the modulated carrier voltage and demodulates the information that is embedded in the input signal. 
         [0038]    Reference is now made to  FIG. 3 , which is a flow chart illustrating a sequence of operations using the system  40  ( FIG. 2 ), in accordance with an embodiment of the presently described subject matter. The process steps are shown in a particular linear sequence for clarity of presentation. However, it will be evident that many of them can be performed in parallel, asynchronously, or in different orders. Those skilled in the art will also appreciate that a process could alternatively be represented as a number of interrelated states or events, e.g., in a state diagram. Moreover, not all illustrated process steps may be required to implement the method. 
         [0039]    At initial step  68  switches  52 ,  64  are both opened. The voltage at energy harvesting component  58  is maximal and it charges the storage capacitor C 5 . When the storage capacitor is charged, the remote unit  48  is ready to work. 
         [0040]    Next, communication step  70  is performed, which comprises two steps  72 ,  74 , which are performed in alternation, i.e., the communication is half-duplex. Any suitable communications protocol may be used: 
         [0041]    In step  72  the remote circuitry  48  transmits data to the signal processing module  50 , modulating a carrier voltage by opening and closing switch  64 . Switch  52  remains open during step  72 . 
         [0042]    In step  74  the signal processing module  50  transmits commands to the remote circuitry  48 , modulating the carrier voltage by opening and closing switch  52 . Switch  64  remains open during step  74 . 
         [0043]    It should be noted that the remote circuitry  48  is fully isolated from the power circuitry  42 . There is no common ground connection between the two components. If a short between the wires of the wire pair  66  should occur, the patient would be exposed only to a low voltage. Disconnection would result in a higher voltage than normal but still within a low range, so that patient safety would not be compromised. For example, if the generator&#39;s output voltage is no more than  2 V and resistors R 1 , R 2  are in the range of 50 kΩ, the maximum current through the patient&#39;s body would be 2V/100 kΩ=20 uA. In this regard, it may be noted that the maximum allowable current through the patient&#39;s body in a single fault condition according to the standard IEC60601-1 is 50 uA. 
         [0044]    It will be appreciated by persons skilled in the art that the presently described subject matter is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present presently described subject matter includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof that are not in the prior art, which would occur to persons skilled in the art upon reading the foregoing description.