Abstract:
Methods and systems of catheterization include a flexible catheter adapted for insertion into a heart of a living subject. The catheter has a lumen for passing an electrically conductive fluid therethrough, which is propelled by a peristaltic pump. A fluid reservoir connected to the lumen supplies the fluid to the catheter. Electrocardiogram circuitry is connectable to the subject for monitoring electrical activity in the heart. An electrically conductive cable diverts induced charges in the fluid from the catheter electrodes, for example by shorting to a rotating element in the peristaltic pump.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to medical catheterization. More particularly, this invention relates to electrocardiographic monitoring during medical catheterization procedures. 
         [0003]    2. Description of the Related Art 
         [0004]    The meanings of certain acronyms and abbreviations used herein are given in Table 1. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Acronyms and Abbreviations 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 ECG 
                 Electrocardiogram 
               
               
                   
                 PIU 
                 Patient Interface Unit 
               
               
                   
                 RF 
                 Radiofrequency 
               
               
                   
                   
               
             
          
         
       
     
         [0005]    Medical catheterizations are routinely carried out today. For example, in cases of cardiac arrhythmias, such as atrial fibrillation, which occur when regions of cardiac tissue abnormally conduct electric signals. Procedures for treating arrhythmia include surgically disrupting the origin of the signals causing the arrhythmia, as well as disrupting the conducting pathway for such signals. By selectively ablating cardiac tissue by application of energy, e.g., radiofrequency energy via a catheter, it is sometimes possible to cease or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions. 
         [0006]    A known difficulty in the use of radiofrequency energy for cardiac tissue ablation is controlling local heating of tissue. There are tradeoffs between the desire to create a sufficiently large lesion to effectively ablate an abnormal tissue focus, or block an aberrant conduction pattern, and the undesirable effects of excessive local heating. If the radiofrequency device creates too small a lesion, then the medical procedure could be less effective, or could require too much time. On the other hand, if tissues are heated excessively then there could be local charring effects due to overheating. Such overheated areas can develop high impedance, and may form a functional barrier to the passage of heat. The use of slower heating provides better control of the ablation, but unduly prolongs the procedure. Commonly assigned application Ser. No. 13/339,782, which is herein incorporated by reference, discloses the use of an irrigation pump to cause irrigation fluid to flow through a lumen of the catheter in order to cool the ablation site. 
       SUMMARY OF THE INVENTION 
       [0007]    There is provided according to embodiments of the invention a catheterization system, which avoids spurious electrical interference in electrical monitoring circuitry when a peristaltic pump is operating to irrigate an ablation site. The system includes a flexible catheter adapted for insertion into a heart of a living subject. The catheter has a lumen for passing an electrically conductive fluid therethrough to exit the catheter at its distal portion, the lumen connectable to an irrigation pump to form a fluid communication therewith. A fluid reservoir is connected to the lumen for supplying the electrically conductive fluid to the catheter. Electrocardiogram circuitry is connectable to the subject for monitoring electrical activity in the heart. An electrically conductive cable links the electrically conductive fluid to an electrode that is in contact with the subject. 
         [0008]    According to an aspect of the system, the catheter has mapping electrodes disposed on the distal portion and the electrode is located on the catheter proximal to the mapping electrodes. 
         [0009]    According to a further aspect of the system, the electrode is located on a second catheter that is introduced into the subject. 
         [0010]    According to one aspect of the system, the catheter has an inlet port, and a connector electrically contacts the electrically conductive fluid at the inlet port, and connects the electrically conductive fluid to a patient ground. 
         [0011]    According to another aspect of the system, the electrically conductive cable is electrically connected to the electrically conductive fluid downstream of the irrigation pump. 
         [0012]    According to an additional aspect of the system, the electrically conductive cable is a metallically shielded cable. 
         [0013]    There is further provided according to embodiments of the invention a catheterization system, including a flexible catheter adapted for insertion into a heart of a living subject. The catheter has a lumen for passing an electrically conductive fluid therethrough to exit the catheter at its distal portion. A fluid reservoir is connected by a hydraulic line to the lumen for supplying the electrically conductive fluid to the catheter. The system includes a pump for propelling the electrically conductive fluid to the lumen of the catheter. The pump has a rotating element that acts upon the hydraulic line. An electrically conductive cable forms an electrical connection between the electrically conductive fluid in the hydraulic line and the rotating element. 
         [0014]    According to an additional aspect of the system, the rotating element is metallic. 
         [0015]    According to another aspect of the system, the rotating element is formed from a ceramic. 
         [0016]    According to yet another aspect of the system, the rotating element is formed from a polymer. 
         [0017]    According to still another aspect of the system, the rotating element is formed from an acetal homopolymer. 
         [0018]    According to yet another aspect of the system, the electrically conductive cable connects to the frame of the pump. 
         [0019]    According to still another aspect of the system, the electrically conductive cable connects to the rotating element of the pump. 
         [0020]    According to an additional aspect of the system, the rotating element is electrically non-conductive. 
         [0021]    According to one aspect of the system, the electrical connection with the electrically conductive fluid is downstream from the pump. 
         [0022]    According to a further aspect of the system, the electrical connection with the electrically conductive fluid is upstream from the pump. 
         [0023]    According to one aspect of the system, a portion of an outer surface of the hydraulic line is coated with an antistatic chemical, including the portion contacting the outer surface with the rotating element of the pump. 
         [0024]    According to one aspect of the system, the contacting portion of an outer surface of the hydraulic line is coated with an antistatic chemical selected from the group consisting of soap water, saline and water. 
         [0025]    According to a further aspect of the system, the contacting portion of an outer surface of the hydraulic line is coated with an electrical conductor. 
         [0026]    There is further provided according to embodiments of the invention a method for monitoring electrical activity, which is carried out by connecting a reservoir of an electrically conductive fluid to a peristaltic pump having a rotating element, wherein the peristaltic pump exerts a force on a hydraulic line to cause the electrically conductive fluid to flow through the hydraulic line. The method is further carried out by connecting electrocardiogram circuitry to the subject, forming an electrical connection between the electrically conductive fluid and the peristaltic pump, and while operating the peristaltic pump, monitoring electrical activity in the heart with the electrocardiogram circuitry. 
         [0027]    Yet another aspect of the method a portion of the hydraulic line is coated with an electrical conductor and the portion in contact with the rotating element. 
         [0028]    According to still another aspect of the method, the electrical conductor is indium tin oxide. 
         [0029]    According to an additional aspect of the method, the electrical conductor is aluminum foil. 
         [0030]    In a further aspect of the method the outer surface of the contacting portion of the hydraulic line is coated with a material containing liquid water and an ionic surfactant. 
         [0031]    An additional aspect of the method includes coating an outer surface of a portion of the hydraulic line with an anti-static chemical additive. 
         [0032]    According to still another aspect of the method the contacting portion of the hydraulic line is impregnated with an anti-static chemical. 
         [0033]    According to one aspect of the method a portion of an outer surface of the hydraulic line is coated with an anti-static chemical and includes the portion in contact with the rotating element. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0034]    For a better understanding of the present invention, reference is made to the detailed description of the invention, 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: 
           [0035]      FIG. 1  is a pictorial illustration of a system for performing catheterization procedures on a heart of a living subject, which is constructed and operative in accordance with an embodiment of the invention; 
           [0036]      FIG. 2  is a schematic diagram of aspects of a cardiac catheterization irrigation system that illustrates electrical events that occur during operation, in accordance with an embodiment of the invention; 
           [0037]      FIG. 3  is a schematic diagram of a test arrangement for measuring electrocardiogram noise reduction, in accordance with an embodiment of the invention; 
           [0038]      FIG. 4  is a schematic diagram of a connector for establishing electrical continuity between fluid and an electrical cable, which is constructed in accordance with an embodiment of the invention; 
           [0039]      FIG. 5  is a schematic diagram of a system for reducing electrocardiogram noise, in accordance with an alternate embodiment of the invention; 
           [0040]      FIG. 6  shows three charts of recorded ECG data when the system shown in  FIG. 5  is in operation, in accordance with an embodiment of the invention; 
           [0041]      FIG. 7  is a schematic of a system for reducing electrocardiogram noise, in accordance with an alternate embodiment of the invention; 
           [0042]      FIG. 8  is a schematic diagram of an infusion system, in accordance with an alternate embodiment of the invention; and 
           [0043]      FIG. 9  is a schematic diagram of an arrangement of an infusion system, in accordance with an alternate embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0044]    In the following description, numerous specific details are set forth in order to provide a thorough understanding of the various principles of the present invention. It will be apparent to one skilled in the art, however, that not all these details are necessarily always needed for practicing the present invention. 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. 
         [0045]    Aspects of the present invention may be embodied in software programming code, which is typically maintained in permanent storage, such as a computer readable medium. In a client/server environment, such software programming code may be stored on a client or a server. The software programming code may be embodied on any of a variety of known non-transitory media for use with a data processing system, such as USB memory, hard drive, electronic media or CD-ROM. The code may be distributed on such media, or may be distributed to users from the memory or storage of one computer system over a network of some type to storage devices on other computer systems for use by users of such other systems. 
       DEFINITIONS 
       [0046]    “Noise” is a disturbance, including a random and persistent disturbance that obscures or reduces the clarity of a signal. 
       System Description 
       [0047]    Turning now to the drawings, reference is initially made to  FIG. 1 , which is a pictorial illustration of a system  10  for performing exemplary catheterization procedures on a heart  12  of a living subject, which is constructed and operative in accordance with a disclosed embodiment of the invention. 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 at an ablation target site. Electrical activation maps, anatomic positional information, i.e., of the distal portion of the catheter, and other functional images may then be prepared using a processor  22  located in a console  24 , 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, which is capable of producing electroanatomic maps of the heart as required. This system may be modified by those skilled in the art to embody the principles of the invention described herein. 
         [0048]    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 from a radiofrequency (RF) generator  40  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. 
         [0049]    The catheter  14  typically comprises 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 positioning processor  22 , located in the console  24 . 
         [0050]    Ablation energy and electrical signals can be conveyed to and from the heart  12  through the catheter tip and an ablation electrode  32  located at or near the distal tip  18  via cable  34  to the console  24 . Pacing signals and other control signals may be also conveyed from the console  24  through the cable  34  and the ablation electrode  32  to the heart  12 . Sensing electrodes  33 , also connected to the console  24  are disposed between the ablation electrode  32  and the cable  34 . 
         [0051]    Wire connections  35  link the console  24  with body surface electrodes  30  and other components of a positioning sub-system. The electrode  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), typically a thermocouple or thermistor, may be mounted on or near each of the electrode  32 . 
         [0052]    The console  24  typically contains one or more ablation power generators  25 . The catheter  14  may be adapted to conduct ablative energy to the heart using radiofrequency energy. Such methods are disclosed in commonly assigned U.S. Pat. Nos. 6,814,733, 6,997,924, and 7,156,816, which are herein incorporated by reference. 
         [0053]    The positioning processor  22  is an element of a positioning subsystem in the system  10  that measures location and orientation coordinates of the catheter  14 . 
         [0054]    In one embodiment, the positioning subsystem comprises 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 may employ impedance measurement, as taught, for example 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. 
         [0055]    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 . The processor  22  is typically a computer with appropriate signal processing circuits. The processor  22  is coupled to drive a monitor  29 . The signal processing circuits typically receive, amplify, filter and digitize signals from the catheter  14 , including signals generated by the above-noted sensors and a plurality of location sensing electrodes (not shown) located distally in the catheter  14 . The digitized signals are received via cable  38  and used by the console  24  and the positioning system to compute the position and orientation of the catheter  14  and analyze the electrical signals from the electrodes, and generate desired electroanatomic maps. 
         [0056]    The system  10  may include an electrocardiogram (ECG) monitor  37 , coupled to receive signals from one or more body surface electrodes. The ECG signal is typically received through an interface with the console  24 , e.g., a patient interface unit  42  having an analog input and an isolated ground may be used to provide an ECG synchronization signal to the console  24 . 
         [0057]    An electrically conductive fluid, e.g., saline, Ringer&#39;s lactate, is delivered through a lumen  44  in the catheter  14  from a reservoir  46  via a hydraulic line  48 . The electrically conductive fluid is sometimes referred to herein as “saline” for convenience, it being understood that this is by way of example and not of limitation. The lumen  44  terminates in exit pores  50  through which the liquids emerge to cool the electrode  32  and the ablation site. A peristaltic pump  52  is connected to the hydraulic line  48  and causes the fluid to be delivered to the catheter  14  through an entrance port  54  at a desired rate. One difficulty with such an arrangement is that operation of equipment in the environment, e.g., the pump  52 , produces electrical effects, which produce noise that can be picked up by the hydraulic line  48  and can interfere with the analysis and display of the ECG on the monitor  37 . 
         [0058]    The electrical emissions or signals are usually observed in ECG leads connected to a patient who is being transfused or infused with the electrically conductive solution. Any currents that flow in the patient&#39;s body as a result of this potential are sensed as characteristic noise added to the ECG signals. 
         [0059]    This noise has been observed in patients connected to a peristaltic pump for cardiac assist, dialysis treatments and irrigation of an ablation catheter used in treating cardiac arrhythmias. Many sources have been proposed as sources for the noise, some focusing on the pump itself. 
         [0060]    Without being bound by any particular theory, the following discussion is offered to facilitate understanding of the embodiments disclosed herein: 
         [0061]    In one respect the hydraulic line  48  may function as a receiving antenna that collects noise from the surrounding environment and may constitutes one source of the noise. 
         [0062]    In another respect, the pump may be another source of electrical noise, created by a triboelectric effect, whereby an induced charge is created on the surface of flexible tubing used in the pump and on the surface of the rotor surfaces used to compress the tubing. The rubbing or deforming action of the rotor against the tubing surface displaces electrical charge. Some of the charge is collected on the rotor and some is collected on the tubing surface. The tubing wall is generally an insulator, so that the external charge on the outside surface of the tube is induced on the inside of the tubing bore if the fluid in the tubing is an electrical conductor. In consequence, a generator potential appears between the electrically conductive fluid and the pump rotor. Any electrical circuit connecting these two points allows current to flow. Such current, if sensed or intercepted by the EKG circuitry, produces undesirable signals on the EKG tracing that are perceived as “ECG noise” by the operator. Because the triboelectric potential appears in series with the capacitance of the external and internal tubing walls, which are generally insulators (plastic), the triboelectric current has bursty characteristics. 
         [0063]    Additionally or alternatively, The observed current may arise from a piezoelectric effect in the tubing walls. 
         [0064]    Further additionally or alternatively, there appears to be a strong amplification mechanism resulting from the motion of the tubing walls as they are squeezed between the rotor rollers and the pump race, causing a dynamic change in tubing capacitance, which is in series with the triboelectric charge. 
         [0065]    The noise, as observed on an ECG leads, appears as spikes, making the ECG signals difficult to interpret, and these spikes can even be confused as ECG waves themselves. Additionally, a fast Fourier transform applied to the noise to obtain its power spectrum finds component sinusoids at repetition frequencies equal to the impact rate of the rotor rollers (N) on the tubing surface along with higher harmonics. The repetition frequencies are dependent on the number of rollers in a rotor, and are to be distinguished from the rotor rotation rate itself. 
       First Embodiment 
       [0066]    In one embodiment, the inventors have found that connecting an electrically conductive wire  56  between the electrolytic fluid, e.g., between the peristaltic pump effects a significant reduction in the electrical interference. 
         [0067]    In order to minimize the number of conductors in the area of operation, the wire  56  may be incorporated in the hydraulic line  48  leading from the reservoir  46 . 
         [0068]    Reference is now made to  FIG. 2 , which is a schematic diagram of aspects of a cardiac catheterization irrigation system  58 , and which illustrates certain electrical events that occur when the system  58  is used in medical procedures, and which are modified in according to embodiments of the invention. 
         [0069]    In the system  58 , saline  60  stored in an intravenous (I.V.) bottle or reservoir  62  is propelled by a peristaltic pump  64  through tubing  66 , which is typically polyvinyl chloride (PVC) tubing. The pump  64  comprises a rotating contact  68 , which typically includes a metallic rotor or race and metallic bearings, e.g., roller bearings. The fluid continues through the tubing  66 , and thence through a catheter  70 , terminating in its distal segment  72  where various electrodes are disposed, including sensing electrode  74 , and ablation electrode  76 . 
         [0070]    A triboelectric effect occurs in parts of the system  58 , particularly where the rotating contact  68  of the pump  64  compresses the tubing  66 , which causes an triboelectric charge to build up in the saline  60 . The charge flows through the tubing  66 , propagating downstream and forming a circuit through the ablation electrode  76 , and returning to the pump  64  via the patient&#39;s body as shown in  FIG. 2 . It is believed that the triboelectric generator in the irrigation system contributes to the spurious signals seen on the electrocardiogram. Any disturbance of the triboelectric generator or interruption or diversion of the closed loop generator current so that it does not pass through the ECG electrodes is sufficient to suppress this noise to a variable degree. 
         [0071]    There are several ways to minimize the electrical potential that is generated between the saline and surrounding conductors and thereby mitigate the spurious signals. 
         [0072]    1) In general, the capacitance between components may be reduced by adjusting any or all parameters in the generic capacitance equation: 
         [0000]        C=e 0* eR *(EffectiveArea/EffectiveSeparation), 
         [0073]    where C is capacitance; e0 is the vacuum dielectric constant; and eR is the relative dielectric constant of insulators or semi-insulators placed between the exterior boundary of the tubing and any conductors constituting a return path for the generated charge. The effective area (EffectiveArea) of those conductors is the effective electrical surface area of the components, and the effective separation (EffectiveSeparation) is the effective distance measured parallel to the electric field induced by the charge separation and perpendicular to the plane of the surface area upon which said charge resides. 
         [0074]    Replacing metallic roller bearings and race with non-conductive equivalents, such as ceramic or polymer, reduces eR from a large number (&gt;1000) to between 1 and 11 for common ceramic dielectrics. As an example, the race could be replaced with Delrin®, available from E. I. DuPont de Nemours &amp; Co., Wilmington, Del. 19898. Delrin is a tough, “non-wearing” acetal homopolymer with an eR value of about 2.5. The thicker the race, then the lower the capacitance. Replacing the roller bearings with plastic or ceramic will also accomplish the same reduction in capacitance. Even replacing the cavity in which the steel rollers turn with a ceramic pocket will reduce the capacitance. 
         [0075]    Altering the physical or chemical composition of the PVC tubing may suppress charge separation. The extrusion process that forms the tubing has the effect of orienting and aligning the PVC molecular strands. Aligned solids of this sort have piezoelectric characteristics, and can produce charge from mechanical compression. By randomizing the molecular strands through a heat treating process or adding an electrically conducting material to the PVC, the charge separation potential can be largely mitigated by preventing the physical process that creates it or by effectively shorting it out. 
         [0076]    A generative component for the observed charge buildup could also be related to the collapse of an electric dipole layer, which forms at the interface between the saline and the plastic tubing walls when the rollers crush the walls of the tubing altering the Zeta potential. To deal with this effect, a surface treatment applied to the inside of the tubing bore could be engineered to suppress the initial formation of the dipole layer. For example, a highly symmetric chemical structure or a very long uncharged alkyl chain would effectively weaken the usual short highly polar ionic dipoles that normally form. While the dipole strength may be weakened by reducing the ionic strength or molality of the saline at the pump, this is inconvenient because it would involve complex mixing components in order to satisfy human physiologic requirements. 
       Example 
       [0077]    Reference is now made to  FIG. 3 , which is a schematic diagram of a test arrangement  114  using an RF signal generator, in accordance with an embodiment of the invention. An intravenous infusion pack  116 , containing saline, constitutes an electrolyte fluid reservoir, as described above. An electrical cable  118 , leading from a line  124  downstream of a drip chamber  112 , is connected to saline  138  in an aquarium  150 . The saline flows from the drip chamber  112  through a connector  120  to reach the line  124 , and is in electrical contact with the cable  118 . The line  124  extends from the connector  120  to a pump  126 . 
         [0078]    Hydraulic lines  124 ,  128  interconnect the intravenous infusion pack  116 , and the pump  126 . An electrical Line  130  connects a handle  132  and a catheter  134  with an RF generator  136 . The line  128  extends from the pump  126  to the handle  132  of catheter  134 . The distal end of the catheter  134  is inserted into the aquarium  150  containing saline  138 , which emulates a human subject. 
         [0079]    A test system  140  includes ECG circuitry  142 , which is connected to a display  144 . Four ECG leads  146  are connected to the ECG circuitry  142  and to metal patches  148  that are mounted on the internal surfaces of the aquarium  150  in contact with the saline  138 . The electrical cable  118  connects the intravenous infusion pack  116  to the saline  138  in the aquarium  150 . 
         [0080]    Reference is now made to  FIG. 4 , which is a schematic diagram of the connector  120  ( FIG. 3 ), which is constructed in accordance with an embodiment of the invention. The connector  120  is tubular, having an outer metal shell  154 , and a lumen filled with an electrically conductive net or sponge  156 . The sponge  156  assures extensive physical contact with saline flowing in the lumen of the connector  120 , and increases its conductance. An electrical connector  158  is provided on the metal shell  154  so that electrical continuity exists between the saline in the lumen, the sponge  156  and the cable  118 . 
       Second Embodiment 
       [0081]    Reference is now made to  FIG. 5 , which is a schematic of a system  178  for reducing electrocardiogram noise, in accordance with an alternate embodiment of the invention. In this embodiment electrolyte-containing fluid in a reservoir  220  is pumped into an intravascular catheter  222  by a pump  224  is electrically connected to a subject  180  by a connector  226  and an electrically conductive cable  182 , for example using a body surface electrode pad or needle electrode  184  attached to a limb or other portion of the body of the subject  180 , or to a patient ground. The connector  226  may have the same structure as the connector  120  ( FIG. 4 ), The cable  182  may be shielded. The connector  226  is placed in a hydraulic line  228  or on a stopcock downstream from the reservoir  220 . Preferably the connector  158  is disposed downstream of the pump  224 . 
         [0082]    Reference is now made to  FIG. 6 , which presents recorded ECG data when the system  178  ( FIG. 5 ) is in operation, in accordance with an embodiment of the invention. The data were recorded using the CARTO 3 system, a NaviStar® Thermo-Cool® catheter, and a SmartAblate™ pump (available from Cordis Corporation). The RF ablation generator was not active. An aquarium was used to simulate a patient, as described above with reference to  FIG. 3 . 
         [0083]    ECG strip  232  is a baseline tracing, before attachment of the cable  182 . Background noise is shown, with a magnitude of about 0.02 mV. 
         [0084]    In ECG strip  234  the pump is active. Noise has increased to a value of about 0.07 mV. 
         [0085]    In ECG strip  236  the pump remains in operation. The cable  182  has been connected thereby shorting the saline in the irrigation tubing to saline bath water. The noise level has returned to the baseline value of about 0.02 mV. 
       Third Embodiment 
       [0086]    Reference is now made to  FIG. 7 , which is a schematic of a system  188  for reducing electrocardiogram noise, in accordance with an alternate embodiment of the invention. The arrangement in  FIG. 7  is similar that of  FIG. 5 . However, a wire  238  now extends from the connector  226  to an electrode  240  located on the catheter  222 , but proximal to electrodes  32  and  33 , for example in the inferior vena cava. 
         [0087]    Alternatively, the electrode  240  may be disposed on a second catheter (not shown), which has been introduced into the subject, for example into the vascular system or the gastrointestinal tract. The wire  238  is rerouted to the electrode  240  mutatis mutandis. 
       Fourth Embodiment 
       [0088]    Reference is now made to  FIG. 8 , which is a schematic diagram of an arrangement  204  of an infusion system, in accordance with an alternate embodiment of the invention. In this embodiment, a saline solution  205  in tubing  206  is shorted to a peristaltic pump  208  using a wire  210  that extends from a connector  212  to a metal rotor  214  or rollers in the pump  208 . The wire  210  electrically connects the saline solution  205  that is propelled by the pump  208  through the tubing  206 , thereby shorting out the tribo-generator. The connection may alternatively be realized by an electrically conductive nipple whose inside surface is in contact with the saline and whose body is connected to the current return side of the pump rotor. ECG data is obtained via PIU input  102  in console  186  from electrode  241  on catheter  242   
         [0089]    The arrangement  204  has been tested using a saline surrogate for a patient tissue model similar to the test arrangement shown in  FIG. 3 . The irrigation peristaltic pump pushes normal saline through tubing connected to the nipple and further attached to an irrigated catheter within the patient&#39;s body. The current flowing through the saline channel in the catheter and into the patient is the source for the ECG noise signal. 
       Fifth Embodiment 
       [0090]    Reference is now made to  FIG. 9 , which is a schematic diagram of an arrangement  216  of an infusion system, in accordance with an alternate embodiment of the invention. The arrangement  216  is similar to the arrangement  204  ( FIG. 8 ). However, shorting the generator potential is accomplished by forming an electrical connection between the pump  208  and the drip chamber  112  or other fluid source feeding the input side of the pump by a wire  218  or by a conductive nipple. By shorting the saline in tubing  206  to the rotor or pump frame, the generator potential is effectively short circuited on the input side of the pump  208  rather than on the output side as in the previous embodiment. 
       Sixth Embodiment 
       [0091]    Referring again to  FIG. 9 , the embodiments described above can be further modified by mitigating the surface charge of the tubing. One way to accomplish this is by coating the outer surface of the tubing or hydraulic line with any material containing liquid water and an ionic surfactant that renders the water slightly electrically conductive and the tubing surface hydrophilic. Coating may be accomplished by squirting, spraying, or rubbing saline, hand soap or electrode gel on the outside of the tubing. While the foregoing description applies to a very broad class of substances, it has been found that certain materials were particularly effective in disrupting the triboelectric generator, namely ordinary hand soap, saline, and electrode gel. 
         [0092]    Non-conductors such as lubricating oil were also tested in an attempt to disrupt the surface of the triboelectric generator. These altered the potential depending on how dry or poorly conductive the oil. Dry or poorly conductive oil was less effective than oil mixed with water or having conductive properties. Oil mixed with three-micron aluminum flakes constitute a very effective disrupting agent, but do not completely suppress the potential, because the conduction mechanism appears to be capacitive coupling between aluminum particles, rather than ionic conductivity as in water. As soon as the water in any of these preparations evaporates, the triboelectric generator returns to its original potential, reinstituting electrical noise. 
         [0093]    Alternatively, the outer surface of the tubing may be coated with an electrical conductor, so that mechanical contact with the metallic rotor  214  is essentially metal-on-metal. Indium tin oxide is suggested. Wrapping the tubing in aluminum foil so that the contact point is metallic roller on foil completely eliminates triboelectric charging. 
         [0094]    Alternatively, impregnating the plastic material of the tubing with anti-static chemical additives, e.g., metal particles, so that the tubing walls are slightly conductive, shorts out the triboelectric generator. These chemical additives tend to be hydrophilic attracting water molecules to bind with the plastic surface or volume so that it is slightly electrically conductive. 
         [0095]    Further alternatively, adding “anti-static” chemical additives to the outer surface of the tubing is also effective. 
         [0096]    It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention 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.