Abstract:
A device having a combined electrode (20) and position tracking transducer (30) mounted to a surgical instrument, such as a catheter (10). In a preferred embodiment of the invention, the electrode (20) serves dual functions, namely as a standard ECG electrode for communicating an ECG voltage, and as an electrode transducer, such as a conductor for a transducer. The combined ECG electrode and position tracking transducer minimizes the amount of space needed on the surgical instrument and the number of required components.

Description:
RELATED APPLICATIONS 
     This is a continuation-in-part of International Application Ser. No. PCT/CA96/00194, filed on Mar. 28, 1996 and now PCT/WO96/31753, which is a continuation in part of Ser. No. 08/411,959 filed Mar. 28, 1995, now U.S. Pat. No. 5,515,853. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to a surgical instrument having both electrodes and transducers mounted thereupon, and more particularly to a catheter having both ECG electrodes and ultrasonic transducers mounted thereupon and sharing the same physical entity. 
     BACKGROUND OF THE INVENTION 
     In electrophysiology applications, mapping and ablating catheters are inserted into a patient&#39;s body and passed along blood vessels until they enter the heart chambers. At that point, the electrocardiogram is mapped by placing the catheter against the internal wall of the heart chambers, the ventricles or the atria. According to the prior art, the mapping process involves visualizing the mapping catheter inside the heart using continuous fluoroscopy, which creates a shadow of the catheter that moves with the heart as the physician manipulates the catheter. 
     Since the manipulation of these types of catheters is difficult and time consuming, and fluoroscopy subjects patients and doctors to considerable doses if x-ray, an ultrasound based catheter guidance system, such as described in U.S. Pat. No. 5,515,853 and incorporated herein by reference, is used to display the position and motion of the catheter as a 3-D graphic. The catheter guidance system makes use of transit time ultrasound to measure the distance between an array of ultrasonic transducers. Some of the transducers (i.e. &#34;mobile transducers&#34;) are mounted to catheters inserted into the patient&#39;s body, and other transducers are affixed to the patient at fixed locations (i.e. &#34;reference transducers&#34;) to provide internal and/or external reference frames. A large matrix of distances between many combinations of transducers is obtained many times per second, and then converted into 3-dimensional x,y,z coordinates for each transducer. The motion of the catheter affixed with such ultrasonic transducers can then be tracked in 3-D space, relative to the position of the reference transducers. 
     Using the time-of-flight principle of high frequency sound waves, it is possible to accurately measure distances within an aqueous medium, such as inside the body of a living being during a surgical procedure. High frequency sound, or ultrasound, is defined as vibrational energy that ranges in frequency from 100 kHz to 10 MHz. The device used to obtain three-dimensional measurements using sound waves is known as a sonomicrometer. Typically, a sonomicrometer consists of a pair of piezoelectric transducers (i.e., one transducer acts as a transmitter while the other transducer acts as a receiver). The transducers are implanted into a medium, and connected to electronic circuitry. To measure the distance between the transducers, the transmitter is electrically energized to produce ultrasound. The resulting sound wave then propagates through the medium until it is detected by the receiver. 
     The transmitter typically takes the form of a piezoelectric crystal that is energized by a high voltage spike, or impulse function lasting under a microsecond. This causes the piezoelectric crystal to oscillate at its own characteristic resonant frequency. The envelope of the transmitter signal decays rapidly with time, usually producing a train of six or more cycles that propagate away from the transmitter through the aqueous medium. The sound energy also attenuates with every interface that it encounters. 
     The receiver also typically takes the form of a piezoelectric crystal (with similar characteristics to the transmitter piezoelectric crystal), that detects the sound energy produced by the transmitter and begins to vibrate in response thereto. This vibration produces an electronic signal in the order of millivolts, that can be amplified by appropriate receiver circuitry. 
     The propagation velocity of ultrasound in an aqueous medium is well documented. The distance traveled by a pulse of ultrasound can therefore be measured simply by recording the time delay between the instant the sound is transmitted and when it is received. 
     A typical electrophysiology catheter takes the form of a polymeric tube with metallic electrodes arranged as rings near its distal end. For each electrode, there is an electrical conductor that runs the length of the catheter shaft and exits at a connector at the proximal end of the catheter to transmit signals to and from the electrode. In order to track the position of the catheter using an ultrasonic catheter guidance system, the catheter must be fitted with appropriate ultrasonic transducers (i.e. &#34;mobile transducers&#34;). These transducers take up space near the mapping portion of the catheter where the electrodes are located, and must also have electrical conductors within the catheter to transmit signals to and from the transducers. In most cases, each ultrasonic transducer requires two additional conductors within the catheter. 
     The additional space occupied by -the ultrasonic transducers, as well as the many additional conductors needed to be passed through the catheter are undesirable. In this respect, the distal end of the catheter is often intended to deflect, and through the addition of rigid members (i.e., transducers) to the catheter, the ability of the catheter to easily bend is reduced. Moreover, it is important to note that there is finite space inside a catheter for electrodes. Therefore, there is a need to minimize the space taken by the ultrasonic transducers on the catheter, as well as a need to reduce the number of extra conductors within the catheter shaft. 
     The present invention overcomes these and other drawbacks of prior devices and provides a method and apparatus which minimizes the amount of space needed on a catheter to include ultrasonic transducers, and minimizes the number of electrical conductors arranged within the catheter shaft. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided an instrument having a combined electrode and transducer sharing the same physical entity. 
     It is an object of the present invention to provide a merged electrode and transducer mountable to an instrument, wherein the electrode is adapted for mapping or ablation and the transducer is suitable for tracking the position of the instrument. 
     It is another object of the present invention to provide an instrument having an electrode and a transducer arranged in the same physical entity. 
     It is another object of the present invention to provide a catheter having a mapping or ablation electrode and an ultrasonic transducer, wherein the space taken up by the ultrasonic transducer on the catheter is minimized. 
     It is still another object of the present invention to provide a catheter having a combined mapping or ablation electrode and ultrasonic transducer, wherein the number of conductors located within the catheter shaft are minimized. 
     It is yet another object of the present invention to provide a catheter having a combined mapping or ablation electrode and ultrasonic transducer, wherein conductors between the mapping electrodes and ultrasonic transducers are shared. 
     These and other objects will become apparent from the following description of a preferred embodiment of the present invention taken together with the accompanying drawings and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take physical form in certain parts and arrangements of parts, a preferred embodiment and method of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof, and wherein: 
     FIG. 1 is a side perspective view of a catheter illustrating a preferred embodiment of the present invention; 
     FIG. 2 is a sectional side view of the catheter shown in FIG. 1; and 
     FIG. 3 is a block diagram showing the circuitry of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings wherein the showings are for the purposes of illustrating a preferred embodiment of the invention only and not for purposes of limiting same, FIG. 1 shows a catheter 10 having ultrasonic transducers 30 and electrodes 20 mounted to the distal end of a catheter shaft 12. Transducers 30 are comprised of an annular outer conductor 24, an annular inner conductor 26 and a ring of piezoelectric material 40, which is arranged therebetween, as shown in FIG. 2. Outer conductor 24 also serves as electrode 20. Piezoelectric material preferably takes the form of a piezoelectric crystal. By using outer conductor&#39;s surfaces 24 as mapping electrodes 20, no additional space is required on the catheters for the transducers 30. It should be appreciated that outer conductor 24 and inner conductor 26 may take the form of a metallic plating or film. 
     While a preferred embodiment of the present invention will be described with reference to &#34;mapping&#34; electrodes, electrodes 20 may take the form of other types of electrodes including ablation electrodes, mapping baskets, plates, and strips. Moreover, other types of instruments can be substituted for catheter 10, including probes, sensors, needles and the like. 
     Shaft 12 of catheter 10 is arranged through opening 28 formed by annular inner conductor 26. A pair of electrode/transducer conductor leads 50 extend respectively from outer conductor 24 and inner conductor 26. Conductor leads 50 extend through ducts formed in catheter 10. The first lead is a ground conductor lead 54 and the second lead is a power conductor lead 56. 
     Outer conductor 24 serves as mapping electrode 20 and as one of two conductors for transducer 30. Accordingly, outer conductor 24 has a dual role of serving both the mapping and tracking functions of catheter 10. During an ECG recording mode of operation, outer conductor 24 will sense the voltage produced by the heart and deliver it through the catheter to external amplifiers. In an ultrasonic tracking mode of operation, outer conductor 24 carries electrical signals to and from transducers 30. In this respect, outer conductor 24 communicates electrical signals from tracking system 70 (e.g., a sonomicrometer) to &#34;fire&#34; transmitter transducers, and communicates electrical signals from receiver transducers, indicating the receipt of a transmitted sound wave. Since these two modes of operation cannot take place simultaneously, a switching system 60 is provided to electrically isolate one mode from the other, as will be described with reference to FIG. 3. Therefore, during an ECG recording mode, tracking system 70 is inhibited from &#34;firing&#34; transducers 30, and the conductor path is switched to the voltage amplifiers that detect the ECG. It should be noted that the term &#34;firing&#34; refers to the action of energizing a transducer to oscillate (thus producing an ultrasonic sound wave) by sending a voltage spike or the impulse function to the transducer. 
     During an ultrasonic tracking mode, the ECG recording amplifiers are switched out and ultrasonic tracking system 70 is activated. It should be appreciated that during the ultrasonic tracking mode, the voltage that is applied to transducers 30 can be as high as a 160 volts. Therefore, it is imperative that this voltage does not appear at outer conductor 24 which is in contact with the patient&#39;s heart. To ensure this, the potential of the patient and the potential of the outer conductor 24 are made equal. In this respect, outer ground lead 54 is provided to electrically ground the outer conductor 24, as well as the patient, during a &#34;firing&#34; cycle. Accordingly, the voltage at inner conductor 26 can be as high as 160 volts, while voltage at outer conductor 24, relative to the patient, is zero. 
     It should be appreciated that the foregoing arrangement of potential switching can be enabled through the appropriate solid state devices, or through micro reed switches that are configured so that the default condition grounds outer ring conductor 24, for the sake of patient safety. The system also has the provision for testing the condition of switching system 60, so that an automatic power down of ultrasonic tracking system 70 is initiated that the patient and outer conductor 24 are not at the same potential (i.e., ground). 
     The foregoing is a description of the specific embodiment of the present invention. It should be appreciated that this embodiment is described for the purpose of illustration only and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the present invention. For instance, the transducers may take the form of electromagnetic transducers and the ultrasonic tracking system may take the form of an electromagnetic tracking system. Moreover, the mapping catheters may be other types of catheters (e.g., ablation catheters) or other surgical instruments (e.g., probes, sensors, etc.). It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof