Abstract:
A catheterization system that includes an electrophysiologic (EP) catheter which has a lumen receiving an electrically conductive fluid delivered by a hydraulic line that is acted upon by a peristaltic pump advantageously avoids noise in intracardiac ECG signal recordings by using an electrical connection to short triboelectrical charge carried by the conductive fluid in the hydraulic line to an existing analog ground in the system. In one embodiment, the electrical connection includes an electrically conductive wire housed in the control handle and configured to provide electrical connection between the fluid and a pin on a printed circuit board housed in the control handle that is electrically connected to the analog ground. In another embodiment, the electrical connection shorts the electrically conductive fluid proximal of the control handle of the catheter.

Description:
FIELD OF INVENTION 
     This invention relates to medical catheterization. More particularly, this invention relates to electrocardiographic monitoring during medical catheterization procedures. 
     BACKGROUND 
     The meanings of certain acronyms and abbreviations used herein are given in Table 1. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Acronyms and Abbreviations 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 ECG 
                 Electrocardiogram 
               
               
                   
                 PIU 
                 Patient Interface Unit 
               
               
                   
                 RF 
                 Radiofrequency 
               
               
                   
                   
               
             
          
         
       
     
     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. 
     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 (now U.S. Pat No. 8,956,353), 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. 
     A typical catheterization system includes a catheter which is inserted through a patient&#39;s vascular system into a chamber or vascular structure of the heart. The catheter&#39;s distal tip is brought into contact with the heart wall for obtaining electrical and positional information that is processed by a console that includes a processor for generating activation maps, anatomical positional information and other functional images. The system typically includes an electrocardiogram (ECG) monitor coupled to receive signals from one or more body surface electrodes. The ECG signal is typically received through an interface with the console, e.g., a patient interface unit having an analog input and an isolated ground may be used to provide an ECG synchronization signal to the console. 
     An electrically conductive fluid, e.g., saline, is delivered through a lumen in the catheter from a reservoir via a hydraulic line. The lumen terminates in exit pores through which the liquids emerge to cool an ablating electrode at the distal portion of the catheter and also the tissue ablation site. A peristaltic pump is connected to the hydraulic line and causes the fluid to be delivered to the catheter at a desired rate. One difficulty with such an arrangement is that operation of equipment in the environment, e.g., the pump produces electrical effects, which produce noise that can be picked up by the hydraulic line and can interfere with the analysis and display of the intracardiac ECG on the monitor. 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. 
     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. 
     Without being bound by any particular theory, the following discussion as set forth in U.S. patent application Ser. No. 13/327,448 (now U.S. Pat. No. 9,101,269), filed Dec. 15, 2001, entitled ELECTROGRAM NOISE REDUCTION, the entire content of which is incorporated herein by reference, is offered to facilitate understanding of the various embodiments described and disclosed herein: In one respect the hydraulic line may function as a receiving antenna that collects noise from the surrounding environment and may constitutes one source of the noise. 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. 
     Additionally or alternatively, the observed current may arise from a piezoelectric effect in the tubing walls. 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. 
     The noise, as observed on intracardiac ECG recordings, appears as spikes, making the ECG signals difficult to interpret, and these spikes (typically ranging between about 0.05 mV and 0.2 mV) 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. 
       FIGS. 8A-8C  illustrate actual ECG recordings with repetitive “spikes” (designated by arrows) in intracardiac ECG signals during ablation procedures using SmartAblate Pump. Analyzing the recordings, it was determined that the frequency of the spikes is proportional to the speed of pump motor (or proportional to the flow rate), such that, for example, for 30 ml/min the spikes occur at about 85 ms time intervals, and for 15 ml/sec the spikes occur at about 170 ms (double the 85 ms time interval). It also appeared that the amplitude of the spikes increased with flow rate (though no linearly), such that the effect was clearly observed only for high flow rates and was indistinguishable for low rates used during mapping/navigation phases. The reported amplitudes of the spikes (measured peak-to-peak) were in the range of about 100-200 μV. It is understood that the noise differs for different pump designs. Time between peaks and peak-to-peak voltage can vary. 
     Treatments to reduce the noise have included lining the pump roller and pump bed, coating the pump hydraulic line with an antistatic chemical, and/or wetting the contact surfaces of these components. However, the reduction tends to be insignificant and/or temporary. 
     The aforementioned U.S. patent application Ser. No. 13/327,448 (now U.S. Pat. No. 9,101,269) describes a hydraulic line having an outer portion coated with a material or an antistatic chemical, including the portion contacting the outer surface with the rotating element of the pump. The material contains liquid water and an ionic surfactant. The antistatic chemical may be selected from the group consisting of soap water, saline and water. In addition, the contacting portion of an outer surface of the hydraulic line may be coated with an electrical conductor, for example, indium tin oxide or aluminum foil. The hydraulic line may also be impregnated with the anti-static chemical. 
     The aforementioned U.S. patent application Ser. No. 131327,448 (now U.S. Pat. No. 9,101,269) also describes a system wherein a 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. 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. According to a further aspect of the system, the electrode is located on a second catheter that is introduced into the subject. 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. According to another aspect of the system, the electrically conductive cable is electrically connected to the electrically conductive fluid downstream of the irrigation pump. According to an additional aspect of the system, the electrically conductive cable is a metallically shielded cable. 
     However, the use of an additional external connection cable increases the burden on an electrophysiology professional by a typical catheterization system which already employs numerous connectors and cables to and from equipment pieces and the patient. Moreover, the use of a cable that links the electrically conductive fluid to an electrode that is in contact with the patient may render the system&#39;s ability to reduce ECG noise dependent on a number of factors, including the quality of the connection between the electrode and patient, the location of the electrode, and the impedance of the patient&#39;s body, which differs from patient to patient. In addition, any added or modified electrical link within the catheterization system may subvert the equipment grounding conductor paths necessary for the system circuit to meet safety requirements. 
     Accordingly, there is a desire for a catheterization system that reduces or eliminates ECG noise. There is a desire that the noise reduction or elimination be accomplished without compromising patient safety or regard to factors, including the quality of the connection between the electrodes and patient, the location of the electrode on the patient, and the impedance of the patient&#39;s body, which differs from patient to patient. There is also a desire for a catheterization system which avoids the use of any additional lengthy cable, especially one that extends between the patient and the fluid source or fluid pump which can tangle or disrupt workflow of the attending medical professionals. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a catheterization system that includes an electrophysiologic (EP) catheter which has a lumen receiving an electrically conductive fluid delivered by a hydraulic line that is acted upon by a peristaltic pump. The present invention recognizes that pump action on the hydraulic line produces a triboelectrical charge that is carried by the conductive fluid in the hydraulic line which can appear as noise in patient ECG recordings detected by an electrode on the catheter. Advantageously, the present invention reduces, if not eliminates, the noise by using an existing isolated ground in the catherization system to reroute the tribo electric charge away from the conductive fluid before the fluid reaches or comes in contact with the catheter electrode. By providing an electrical connection between the existing isolated ground and the conductive fluid at a location proximal of the portion of the catheter in the patient&#39;s body, including electrode(s) at the distal end of the catheter, the triboelectric charge bypasses the catheter electrode which enables the conductive fluid to enter the patient&#39;s body without carrying the triboelectric charge. The electrical “short” or connection to the isolated ground is configured advantageously upstream of any electrode or port in the catheter through which the conductive fluid enters the patient. Thus, the patient&#39;s body remains free of the triboelectric charge that would otherwise disrupt intracardiac signals detected by the catheterization system, or any ECG detection system. The system of the present invention provides an alternate pathway for the triboelectric charge that avoids disruption to and detection by the catheter electrodes or any other electrodes in contact with the patient&#39;s body. The embodiments of the present invention provide an electrical connection that avoids another lengthy cable for the EP operator to connect and monitor, without compromising the safety of the patient. 
     In some embodiments, the electrical connection shorts the electrically conductive fluid inside a control handle of the catheter. In some more detailed embodiments, the electrical connection includes an electrically conductive wire that is housed in the control handle and configured to provide electrical connection between the fluid and a pin on a printed circuit board housed in the control handle that is electrically connected to the isolated ground. 
     In some embodiments, the electrical connection shorts the electrically conductive fluid proximal of the control handle of the catheter. In some more detailed embodiments, a wire that extends into the control handle and is electrically connected to the isolated ground has a divergence or split proximal of the control handle into a side wire that is adapted for connection to a luer hub mounted on a distal end of the hydraulic line and adapted to pass the electrically conductive fluid to an irrigation tubing of the catheter. 
     The present invention is not limited to the effects of triboelectric charge but rather the present invention can exclude any other noise that may occur due to hydraulic line, for example, mechanical pressure waves generated in tubing due to back pressure, mechanical pressure waves in catheter lumen due to back pressure, frictional noise, etc. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings. It is understood that selected structures and features have not been shown in certain drawings so as to provide better viewing of the remaining structures and features. 
         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 present invention. 
         FIG. 2  is a schematic circuit diagram of selected electronics of the system of  FIG. 1 . 
         FIG. 3  is an ECG noise measurement experiment setup. 
         FIG. 4A  is an ECG recording of the setup of  FIG. 3 , with no shorting of tribelectric charge. 
         FIG. 4B  is an ECG recording of the setup of  FIG. 3 , with shorting to patient ground. 
         FIG. 4C  is an ECG recording of the setup of  FIG. 3 , with shorting to analog ground. 
         FIG. 5  is a schematic illustration of a pump device. 
         FIG. 6A  is a side view of a catheter control handle of the system of  FIG. 1 . 
         FIG. 6B  is a detailed view of a portion of the catheter control handle of  FIG. 6A . 
         FIG. 7  is a detailed view of a distal end of a catheter cable in accordance with an embodiment of the present invention. 
         FIGS. 8A-8C  are ECG recordings showing “noise” in a conventional catheterization system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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. 
     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 us-ers 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 
     “Noise” is a disturbance, including a random and persistent disturbance that obscures or reduces the clarity of a signal. 
     System Description 
     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 or patient  13 , 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 electrophysiologist or operator  16  through the patient&#39;s vascular system into a chamber or vascular structure of the heart  12 . The catheter  14  has a distal tip  18  carrying one or more electrodes  32  and  33 , and a control handle  20  by which the operator can manipulate to steer and deflect the catheter. 
     The operator  16  brings the catheter&#39;s distal tip  18  into contact with the heart wall. 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 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 entire disclosures are herein incorporated by reference. One commercial product embodying elements of the console  24  is the CARTO® 3 System, available from Biosense Webster, Inc., 3333 Diamond Canyon Road, Diamond Bar, Calif. 91765, which performs catheter localization and produces 3-D 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. 
     Areas determined to be abnormal, for example by evaluation of electrical activation maps, can be targeted and ablated by application of thermal energy, e.g., by passage of radiofrequency electrical current from a radiofrequency (RF) generator  25  of the console  24  through a cable  34  providing current to the catheter, including the ablation electrode  32  at the distal tip  18 , which apply the radiofrequency energy to target tissue. The energy is absorbed in the tissue, heating it to a point 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 console  24  typically contains one or more ablation power generators  25 . The catheter  14  is 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. Ablation energy is conveyed from RF generator  25  to the heart  12  through the catheter tip, including irrigated ablation electrode  32 , via cable  34  which is connected to the console  24 . Pacing signals and other control signals may also be conveyed from the console  24  through the cable  34  and the ablation electrode  32  to the heart  12 . Moreover, electrical signals (for example, intracardiac ECG signals) are conveyed from the heart  12  to the console  24  through the catheter tip, including the irrigated ablation electrode  32  and one or more nonirrigated ring electrodes  33 , and the cable  34 . A temperature sensor (not shown), typically a thermocouple or thermistor, may be mounted on or near each of the catheter electrodes. 
     As part of the system  10 , ECG body surface patches, including at least patches  38 RA,  38 LA,  38 RL and  38 LL are affixed to the patient&#39;s body. While the catheter electrodes  32  and  33  are sensing intracardiac ECG signals, a plurality of electrodes in the ECG body surface patches  38 RA,  38 LA,  38 RL and  38 LL measure ECG signals across the heart and torso to provide reference signals for the intracardiac ECG signals measured by the catheter electrodes. 
     As part of the catheter localization capabilities of the console  24 , a magnetic field is generated around the patient  13 , for example, by a location pad containing magnetic field generator coils  28  that is placed under the patient. The magnetic fields generated by coils  28  generate electrical signals in coils of an electromagnetic (EM) sensor  19  located in the distal tip  18  of catheter  14 . The electrical signals are conveyed to the console  24  which includes a processor  22  that analyzes the signals so as to determine the coordinates of the position and orientation of catheter. 
     As also part of the catheter localization capabilities of the console  24 , the catheter electrodes  32  and/or  33  are connected by lead wires in the catheter  24  and the cable  34  to current and voltage measurement circuitry in the processor  22 . The processor  22  and the console  24  are also connected by wires  35  to a plurality of body surface electrodes  30 , which may be any type of body electrodes known in the art, such as button electrodes, needle electrodes, subcutaneous probes, or patch electrodes. The body surface electrodes  30  are typically in galvanic contact with the body surface of the patient  13  and receive body surface currents therefrom. The body surface electrodes  30  may be adhesive skin patches generically referred to as active current location (ACL patches) and may be placed at any convenient locations on the body surface of the patient  13  in the vicinity of the catheter  14 . In the disclosed embodiment, there are six ACL patches  30 , three affixed on the anterior surface of the patient&#39;s torso and three on the posterior surface. The console  24  comprises voltage generators which are connected via a patch unit  31  and cable  39  to the ACL patches  30  which the processor  22  uses to measure impedance of the patient tissue at the location of the patches  30 . Accordingly, the console  24  uses both magnetic-based position sensing and impedance-based measurements for catheter localization, as described in U.S. Pat. No. 7,536,218, issued to Govari et al., and U.S. Pat. No. 8,478383, issued to Bar-Tal et al., the entire content of both of which are herein incorporated by reference. 
     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  and/or the console  24  include appropriate signal processing circuits and is coupled to drive a monitor  29  to display visual imagery including the 3-D electroanatomical maps. The signal processing circuits typically receive, amplify, filter and digitize signals from the catheter  14 , including signals generated by the above-noted electrodes  32  and  33  and EM sensor  19 . 
     To irrigate the catheter, including the ablation electrode  32 , an electrically conductive fluid, e.g., saline, 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  at the distal tip  18  and in the ablation electrode  32  through which the fluid emerges to cool the tip  18 , 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  at a desired rate through an entrance port, e.g., a luer hub  117 , at the proximal end of a lumened irrigation tubing  115  of the catheter  14 . As shown in  FIG. 5 , the peristaltic pump  52  has a pump bed  51  in contact with a proximal portion of the hydraulic line  48 . As known in the art, the pump  52  has a plurality of rollers  53  driven by a rotor  55  to compress the hydraulic line  48  against the pump bed  51  to advance fluid in the lumen of the hydraulic line  48 . 
     To better understand the triboelectric charging of the surface of the hydraulic line  48  and its translation into the measurable noise spikes on ECG recordings of the catheter electrode  32 , reference is made to  FIG. 2  which is a schematic circuit diagram representative of selected electrical circuits of the system  10 , including a triboelectric noise source  100  applying a voltage across a circuit  120 , that includes an impedance block  101  (representing impedance of the peristaltic pump bed  51 /roller  53 -to-actual ground  109 ), actual ground  109  of the console  24 , an impedance block  102  (representing impedance of the console  24 -to-analog ground  108 ), a patient ground  103 , impedance blocks  104 A and  104 B (representing impedance of patient tissue to irrigated ablation electrode  32 , and impedance of patient tissue to nonirrigated ring electrode  33 , respectively), an impedance block  105  (representing impedance of saline inside catheter irrigation tubing  115 ), an impedance block  106  (representing impedance of saline inside hydraulic line  48 ), and capacitor  107  (representing tubing wall capacitive coupling of the hydraulic line  48 ). As such, noise introduced by the peristaltic pump  52  can be described as traveling along a pathway  111  (shown in solid line) affecting intracardiac ECG readings detected by irrigated electrode  32  and revealing itself as “spikes” in the electrocardiograms shown on the monitor  37  ( FIG. 1 ). 
     The noise source modeled as the voltage source  100  corresponds to the potential created between the hydraulic line  48  and the pump bed  51  and between the hydraulic line  48  and the rollers  53  driven by a rotor  55  due to triboelectric charge. The noise is capacitively coupled to the conductive fluid, e.g., saline, through the tubing wall of the hydraulic line  48  (capacitor  107 ). It is understood that in the embodiment represented by  FIG. 2 , both the pump bed  51  and the rollers  53  are generally isolated from the actual ground  109 , such that their impedances are also generally capacitive. 
     The voltage sampling in the console  24  is performed by differential amplifiers  128 A,  128 B and  128 C, where the reference voltage is the sum of the ECG body surface patches  38 LA,  38 RA and  38 LL. The ECG body surface patch  38  RL is shorted to analog ground  108  through a resistor  129   
     Inspecting the circuit of  FIG. 2 , the system  10  of the present invention offers pathways  131  (single dash) and  132  (double dash) as possible solutions to intracardiac ECG recording noise arising from the triboelectric charge. The system of the present invention recognizes that the circuit  120  can be closed through the ECG body surface patch  38 RL and the isolation impedance of the console  24  (block  102 ). It may serve as an alternative or additional path for the triboelectric charge to travel for eliminating noise by eliminating the current travelling through tip and ring electrode. It is also assumed that no triboelectric current flows to the ECG body surface patches  38 RA,  38 LA,  38 LL,  38 LA, as they have unit gain buffers with very high input impedance. 
     The system further appreciates that for the pathway  111  which results in noise in the intracardiac ECG recordings, the triboelectric current flows through the irrigated catheter electrode  32 , such that the noise is observed on the electrode  32  and no substantial noise is measured on the nonirrigated electrode  33 . (It is understood that different catheters may exhibit different behavior, especially where it has irrigation at more than one catheter electrode.) The difference between the ablation electrode  32  and the ring electrode  33  is due to the irrigation holes of ablation electrode  32  allowing electrode  32  direct contact with the saline carrying the triboelectric charge from the pump  52 . The nonirrigated ring electrode  33 , on the other hand, is separated from the irrigated electrode  32  by relatively high impedance determined by a small surface area of the electrodes. It is understood that with a measured impedance of 100 Ohms (at 480 kHz), most of this impedance is located in the close vicinity of the electrode, while the rest of the saline volume in the patient tissue has much lower impedance. This observation allows the patient impedance to be modeled as two impedances, one from electrode  32  and one from electrode  33 , to the common point referred to as patient ground  103 . 
     Even without the exact values of the impedances, the system  10  of the present invention considers most of the circuit impedances of  FIG. 2  to be dominated by capacitive component, such that the whole circuit has High-Pass behavior. 
     The noise may be measured on the patient tissue impedance which includes impedance block  104 A (representing patient tissue impedance at irrigated electrode  32 ), which is relatively low in comparison to other impedances in the circuit, thus the noise voltage may be generally determined by the following relation:
 
 V   (ablation electrode)   =I   noise   R   Tissue/Body   (Eqn 1)
 
where the noise current is determined by high impedances, for example, ground isolation, tubing wall impedance, saline in the lumen, etc.
 
     Advantageously, the system  10  of the present invention recognizes alternate pathways for the triboelectric charge to travel, wherein the charge can avoid the tip of the catheter, including the irrigated ablation electrode  32 , or any other electrodes on the catheter, including the nonirrigated ring electrode(s)  33 . By electrically connecting the saline in the hydraulic line  48  at a location distal of the pump  52  and proximal of the catheter distal tip  18  to patient ground  103  (via, for example, a cable from hydraulic line connected to surface electrode patches  38 ) to provide pathway  132 , or to analog ground  108  in the catheter  20  to provide  131 , as shown in  FIG. 2 , the catheter, and its electrodes and reference patches (LA, RA, LL and RL) are excluded from the pathway of the triboelectric charge which results in significant noise reduction on intracardiac ECG recordings. 
     An experiment with a nominal setup as illustrated in  FIG. 3  was conducted with no grounding of the triboelectric charge. Accordingly, with the tribo electric current traveling along pathway  111  with no grounding ( FIG. 2 ), intracardiac ECG recordings of  FIG. 4A  included noise “spikes” at about 150 μVp-p. In contrast, with the provision of an electrical connection or “short” between patient ground  103  and the saline in the hydraulic tubing  48 , as shown by pathway  132  (double dash in  FIG. 2 ), the noise spikes in  FIG. 4B  were significantly reduced to about 30 μVp-p. However, with the provision of an electrical connection or “short” between analog ground  108  and the saline in the hydraulic tubing  48 , as shown by pathway  131  (single dash in  FIG. 2 ), the noise spikes of  FIG. 4C  were further reduced down to about 10 μVp-p. 
     This experiment confirmed that grounding saline to either patient ground  103  (pathway  132 ) or the isolated analog ground  108  (pathway  131 ) reduces the measured noise below the required threshold. Notably, shorting saline to patient ground  103  (pathway  132 ) eliminates the noise spikes, but some residual low frequency noise remains, whereas shorting to analog ground  108  (pathway  131 ) can completely eliminate the noise. Shorting to the patient ground  103  does not eliminate noise because the quality of the intracardiac signal sensed by the catheter electrode  32  is dependent on the quality of the reference signal vis-à-vis ECG body surface patches  38 RA,  38 LA,  38 LL,  38 RL which are electrically connected to the patient ground  103 . 
     It is understood that the electrical connection or “short” between the analog ground  108  and hydraulic line  48  (pathway  131 ) is not intended to affect intracardiac ECG signals, because the saline in the lumen of the hydraulic line  48  (a very small diameter) presents a very high impedance (generally of several mega-ohms) and thus, shorting the saline before it enters the catheter does not affect the impedances measured at the catheter distal tip  18 . 
     In accordance with a feature of the present invention, an electrical connection that allows the applied voltage from the triboelectric noise source  100  to be grounded in a manner that bypasses the components of the system at least (1) receiving or in contact with the conductive fluid and (2) in electrical contact with the patient, including irrigated catheter electrode, can significantly reduce, if not eliminate, peristaltic pump noise in intracardiac ECG recordings. 
     In the illustrated embodiment of  FIGS. 6A and 6B , the control handle  20  has barrel housing  63  including a proximal barrel extension  66  whose distal end is inserted in a proximal end of the barrel housing  63 . Extending through the control handle  20  is the irrigation tubing  115  providing the lumen  44 , whose proximal end includes a luer hub  117  adapted for fluid communication with the hydraulic line  48 . Located at the proximal end of the barrel extension  66  is an electrical connector  119  that connects to the cable  34 . The hollow barrel extension  66  houses a printed circuit board (PCB)  65  and associated microprocessor for storing and pre-processing data collected from the sensors  33 . The cable  34  is a standard cable terminated on both ends with multi-pin connectors. The cable  34  connects to the console  24 . As understood by one of ordinary skill in the art, the PCB  65  provides a pin  67  that is connected to the analog ground  108  (see  FIG. 2 ). Because the catheter has electronics for measuring and processing body surface ECG signals as a reference signal for intracardiac ECG signals sensed by the catheter electrodes, the PCB  65  provides the pin  67  connected to the analog ground  108 . 
     In accordance with a feature of the present invention, an electrical connection  110 , for example, a wire or cable  112 , upstream of electrical contacts or connection to the patient  13  allows the triboelectric current arising from interaction between the peristaltic pump  52  and the hydraulic line  48  and imparted to the fluid to avoid the patient  13 . The wire or cable  112  linking the fluid and the PCB pin  67  provides an alternate electrical current pathway (pathway  131  in  FIG. 2 ) for the triboelectric current to pass to the catheter&#39;s existing analog ground  108  via the cable  34 , thereby avoiding the various catheter electrodes, including electrode  32 , and thus the patient  13  who would otherwise come into contact with the catheter electrodes and the charged fluid. By bypassing and avoiding the patient  13 , the triboelectric charge imparted to the fluid is rerouted to the analog ground  108  and diverted from producing. In some embodiments, the wire  112  is provided in the interior of the barrel housing of the control handle  20  and thus has a very short length to fit inside the control handle, as shown in  FIG. 6B . One end of the wire  112  is electrically connected and affixed to the pin  67 , for example, by welding and/or by conductive adhesive. The other end of the wire  112  extends through a hole formed in the side wall of the irrigation tubing  115  and into the lumen  44  to contact the fluid therein. The wire  112  is surrounded by a nonconductive tubing  113 , and because the fluid is under pressure, the nonconductive tubing  113  is affixed to the irrigation tubing  115  and the PCB  56  by a sealant  114  to prevent leakage of the fluid into the interior of the control handle  20 . 
     Alternately, the electrical connection  110  to the isolated analog ground  108  is provided outside and proximal of the control handle  20 . In some embodiments, the system  10  includes a divergence of a wire  116  in the cable  34  that is adapted for connection to the PCB pin  67  in the control handle  20  via the electrical connector  119  at the proximal end of the control handle  20 . As illustrated in  FIG. 7 , the wire  116  diverges or is split into first and second wires  116 A and  116 B. The first wire  116 A continues to extend distally through the cable  34  to its distal connector  127  adapted to connect to the electrical connector  119  at the proximal end of the control handle  20 . The second wire  116 B has a distal end that extends into a male luer connector  133  adapted for connection with a side port  134  of the luer hub  117  in which the distal end of the hydraulic line  48  terminates proximally of the control handle  20 . The wire  116 B, which is made of a biocompatible and sterile material, passes through the male luer connector  133  and the side port  134 , and into the lumen of the luer hub  117  where it comes into contact with fluid passing from the hydraulic line  48  having a male luer connector  135  that is adapted for connection to the irrigation tubing  115  of the catheter via the luer hub  117 . Accordingly, the triboelectric current is rerouted from the lumen of the hydraulic line  48  to the wire  116 B and proximally along the wire  116  in the cable  34  to the console  24 , thus avoiding the electrodes of the catheter and the patient. 
     As discussed above, reported amplitudes of peristaltic pump noise “spikes” (measured peak to peak) can range generally between about 100-200 μV. With the system of the present invention wherein the applied voltage of the triboelectric effect is grounded to an analog ground  108  ( FIG. 2 ) accessible via the PCB  65  in the catheter handle  20 , the noise reduction is absolute and complete, to generally zero, limited by only the sensitivity of the ECG system, for example, about 10 μV, 
     The present invention is not limited to the effects of triboelectric charge but rather the present invention can exclude any other noise that may occur due to hydraulic line, for example, mechanical pressure waves generated in tubing due to back pressure, mechanical pressure waves in catheter lumen due to back pressure, frictional noise, etc. 
     The preceding description has been presented with reference to presently preferred embodiments of the invention. Workers skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structure may be practiced without meaningfully departing from the principal, spirit and scope of this invention. Any feature or structure disclosed in some embodiments may be incorporated in lieu of or in addition to other features of any other embodiments, as needed or appropriate. As understood by one of ordinary skill in the art, the drawings are not necessarily to scale. Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and illustrated in the accompanying drawings, but rather should be read consistent with and as support to the following claims which are to have their fullest and fair scope.