Abstract:
A catheter system including an accelerometer-based sensing assembly is provided. In particular the present teachings relate to an accelerometer based assembly used to determine contact between a catheter and surrounding proximate tissue, such as cardiac tissue. An embodiment of such a system may, for example, be used for visualization, mapping, ablation, or other methods of diagnosis and treatment of tissue and/or surrounding areas.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/347,246, filed 31 Dec. 2008 (the &#39;246 application), now pending. The &#39;246 application is hereby incorporated by reference as though fully set forth herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    a. Field of the Invention 
         [0003]    The present disclosure relates to an accelerometer-based assembly for detecting electrode contact with tissue. 
         [0004]    b. Background Art 
         [0005]    Electrophysiology catheters are used for an ever-growing number of procedures. For example, catheters have been used for diagnostic, therapeutic, mapping and ablative procedures, to name just a few examples. Typically, a catheter is manipulated through the patient&#39;s vasculature and to the intended site, for example, a site within the patient&#39;s heart, and carries one or more electrodes, which may be used for mapping, ablation, diagnosis, or other treatments. 
         [0006]    Techniques of mapping, visualization and treatment using energizing sources, such as radio frequency (RF) ablation, often rely on the placing of an electrode in consistent mechanical contact with targeted tissue. In particular, lesion formation (such as lesions created by exposure to radio frequency), partially depends upon the adequacy of contact between the electrode and tissue. However, there are some challenges. For endocardial applications, the point of electrode-tissue contact is typically 150 cm away from the point of application of force applied by the operator of the catheter outside of the body. This distance complicates making and maintaining good contact between the electrode and tissue. Moreover, the absolute distance, when coupled with the fact that a beating heart is a dynamically moving wall, gives rise to some functional and theoretical challenges, such as ensuring that the electrode is in constant or near-constant mechanical contact with the myocardial wall, or as needed for effective lesion formation. 
         [0007]    Catheter systems having sensor assemblies, such as those mounted on the catheter shaft proximal to the electrode or those mounted remotely in the handle set, leave the possibility, albeit a very small one, of obtaining false positive readings of contact between the electrode and the tissue. Such false positive outcomes may occur, for example, when the catheter wall, and not the electrode, is in contact with the tissue. Such a condition may arise during catheter manipulation in the heart when, for instance, the distal portion of the catheter is curled inwards so much as to lose electrode contact with the tissue, while the distal portion of the catheter is in contact with the tissue. When that happens, remotely placed sensors generate signals due to the deflection of the catheter shaft, thereby falsely indicating contact between the electrode and tissue. 
         [0008]    Additionally, current force sensing methods may be sensitive to thermal changes at an electrode, such as during an ablation procedure. This may lead to incorrect readings of electrode interaction with surrounding tissue. 
         [0009]    There is thus a need for a system and method that minimizes one or more problems as described above. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    Systems and methods are provided for measuring acceleration of an electrode coupled to a medical device, such as a catheter. Measured acceleration of an electrode may be used to determine forces acting on the electrode, and to determine when the electrode is in contact with tissue. The systems described herein may substantially reduce, or eliminate, false positive readings of electrode contact with tissue. 
         [0011]    One or more accelerometers are coupled to an electrode. Signals received from the one or more accelerometers are used to determine either or both of the magnitude and the direction of the acceleration of the electrode. When multiple accelerometers are coupled to the electrode, they may be used in concert with each other to determine acceleration vectors of the electrode. In an embodiment, the force acting on the electrode may be determined from the acceleration of the electrode. For example, the electrode may have a known mass, so the force may be derived by a processor configured to multiply the mass by the acceleration, since Force (F)=Mass (m)×Acceleration (a), i.e. F=ma. Force may also be determined using a lookup table or the like which may be provided in advance for a particular electrode based on the electrode mass, to directly translate acceleration signals into a force indicative parameter. 
         [0012]    An accelerometer may be coupled directly to an electrode, or may be coupled to a carrier disposed between the accelerometer and the electrode. For example, in an embodiment, one or more accelerometers may be coupled directly to a base of an electrode. In such an embodiment, accelerometers are displaced when electrodes are displaced, and the accelerometers thus directly measure electrode acceleration. In another embodiment, accelerometers are coupled to a carrier which is mated to the electrode. In such an embodiment, when forces cause an acceleration of the electrode, forces are transmitted through the carrier. The transmitted forces cause accelerometers to be displaced, or to accelerate. The signals output from the accelerometers can then be used to determine the acceleration of the electrode which caused the acceleration of the accelerometer. This may in turn be used to determine forces acting on the electrode. When the accelerometer is coupled directly to the electrode, a thermally insensitive accelerometer may be used to minimize effects of electrode heat. When accelerometers are separated from an electrode by a carrier, the carrier may be configured to provide a thermally insulative effect, protecting the accelerometer from heat. 
         [0013]    Carriers may take any of a variety of forms. In one embodiment, a carrier may resemble a tripod, having a plurality of legs extending from a central body, where the electrode is mounted to the central body, and accelerometers are mounted to each of the legs. When such an electrode moves, there may be a corresponding movement of the legs. In another embodiment, the carrier may have a cylindrical body with a diaphragm provided across an end. A lever may be attached to the diaphragm, at one end, and to the electrode at the other end, thereby connecting the two. Accelerometers may be mounted on the diaphragm. When a force acts on the electrode, the lever may be moved, transferring the force to the diaphragm. The accelerometers may be configured to measure the acceleration of the diaphragm, and this acceleration may be used to determine the acceleration of the electrode. 
         [0014]    When forces acting on the electrode are determined, they may be analyzed to determine whether the forces are indicative of electrode contact with tissue. This determination may be made in a number of ways. For example, forces acting on an electrode may be compared to forces acting on, e.g., a catheter shaft. If the force acting on the electrode is greater than the force acting on the shaft, this may indicate that the electrode is in contact with tissue. Acceleration may also be compared with the frequency of a heart beat, to determine if accelerations are contemporaneous with the systole and diastole of a cardiac chamber. 
         [0015]    Forces acting on the electrode may also be used for other purposes, such as determining the health of tissue in a particular area. For example, when contact is made between an electrode and heart tissue, the magnitude of the force imparted on the electrode may be indicative of the strength and the health of the tissue. 
         [0016]    In an embodiment, an receiver or controller responsive to the accelerometer signals is configured to indicate to a user at least one of a number of defined parameters, such as (1) an electrode acceleration, (2) a force acting on an electrode, and (3) a degree of electrode-to-tissue contact. The indication may be made using one or more indicators, such as a screen or other visual cue. Additionally, or alternatively, the user (e.g., an electrophysiologist—EP) may be notified only when an electrode is not accelerating, or is no longer in contact with tissue. 
         [0017]    Systems such as those described above may be used during procedures, such as surgical procedures, therapeutic or diagnostic procedures, in many ways. In one embodiment, systems of the invention may be used to ensure ablation electrodes remain in contact with target tissue throughout an ablation procedure. In an embodiment, such systems may be used to determine the force with which heart muscle can repel an electrode, which may be an indicator of the local strength of cardiac tissue, and may be useful in diagnosing heart health. Other methods and uses for the present teachings are also contemplated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a perspective view of a catheter in accordance with an embodiment. 
           [0019]      FIG. 2  is a partial perspective view of the catheter of  FIG. 1 . 
           [0020]      FIG. 3  is an enlarged partial perspective view of the catheter of  FIG. 1 , showing an electrode assembly in accordance with an embodiment. 
           [0021]      FIG. 4  is an enlarged perspective view of an alternate embodiment of an electrode assembly. 
           [0022]      FIG. 5A  is an enlarged perspective view of a further embodiment of an electrode assembly. 
           [0023]      FIG. 5B  is partial cross-sectional view of the electrode assembly of  FIG. 5A  taken substantially along line  5 B- 5 B. 
           [0024]      FIG. 6  is a simplified schematic and block diagram view of an accelerometer-based contact sensing system in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    Referring now to the drawings, wherein like reference numerals are used to identify like components in the various views,  FIG. 1  is a simplified, perspective view of a system  10  for conducting a diagnostic or therapeutic function, which also includes a capability for measuring electrode acceleration. 
         [0026]    The illustrated system  10  includes a catheter  12  operably connected to a controller  14 , which may be an energy source. By way of example, and not of limitation, the catheter  12  may be an RF ablation catheter, and the controller  14  may be an RF ablation generator. Controller  14  may be configured to facilitate the operation of catheter  12 , such as during ablation procedures, and may involve monitoring any number of chosen variables (e.g., temperature of an ablation electrode, ablation energy), and providing a requisite energy source. Additional components, such as visualization, mapping, and navigation components, may also be integrated into the system  10 . For example, an EnSite Electro Anatomical Mapping System  15 , commercially available from St. Jude Medical, Inc., and as also seen generally by reference to U.S. Pat. No. 7,263,397 entitled “Method and Apparatus for Catheter Navigation and Location and Mapping in the Heart” to Hauck et al., owned by the common assignee of the present invention, and hereby incorporated herein by reference in its entirety. Additionally, an electrophysiological monitor or display, such as an electrogram signal display  16 , or other system, may also be integrated into the system  10 . 
         [0027]    Catheter  12  may include a cable connector portion or interface  18 , a handle  20 , and a shaft  22  having a proximal end  24  and a distal end  26 . In the illustrated embodiment, an electrode  28  is disposed on the shaft  22 , near the distal end  26 . Though not illustrated in  FIG. 1 , the stiffness of distal end  26  may be non-uniform along the length thereof. For instance, distal end  26  may include an outermost portion (i.e., axially most remote from the handle) which may have a relative stiffness that is less than the stiffness of contiguous but more proximal areas of the distal end  26 . In an embodiment, forces applied to a shaft  22  may not translate to an electrode  28  coupled to the flexible outermost portion, or may be attenuated at least in part by the relatively flexible outermost portion. Shaft  22  may further include one or more additional electrodes (not pictured), such as ring electrodes, configured for intra-cardiac use. One or more electrodes, such as electrode  28 , may be used for any number of diagnostic and/or therapeutic purposes including, but not limited to, RF ablation, cardiac mapping, electrophysiological studies, and other procedures. Accordingly, the present disclosure is not limited to any one type of catheter or catheter-based system or procedure. Moreover, it should be understood that embodiments consistent with the present invention may include features not shown or described herein for the sake of brevity and clarity. For example, an ablation catheter may typically include additional electrodes (and corresponding leads), a temperature sensor (and corresponding leads), and other features, as known. 
         [0028]    Catheter  12 , and controller  14 , may include structures and functions common to known catheter systems. For example, controller  14  may comprise conventional RF ablation apparatus, such as a commercially available unit sold under the model number IBI-1500T RF Cardiac Ablation Generator, available from Irvine Biomedical, Inc. Of course, controller  14  may also comprise various other known energy sources. In an ablation embodiment, controller  14  may include an ablation generator. In such an embodiment, electrode  28  may be configured to receive excitation energy from the ablation generator, and to output ablation energy to tissue within a treatment area, such as to heart tissue within a cardiac chamber. In such an embodiment, a patch  37  may be provided, which may act as an electrical return for an RE ablation signal. The patch  37  is formed of electrically conductive material to form an electrode, and is configured for affixation to the body of a patient. 
         [0029]    One or more accelerometers  30  (as generally shown in  FIG. 1 ) may be coupled to the electrode  28  within the catheter shaft  22 . The accelerometer  30  may include one or more wires, which may be configured to provide power to the accelerometer  30  and/or to carry a signal indicative of sensed acceleration. Acceleration signals may be provided to a suitable receiver, such as a receiver  17 . Receiver  17  may be configured to receive signals from one or more devices within, or in communication with, catheter  12 . Receiver  17  may include, or may be in communication with, one or more logic systems configured to receive and analyze the received signals. Receiver  17  may be configured to receive a signal from accelerometer  30 , and to determine the acceleration of electrode  28 , or other parameters as will be described in detail below. For example, receiver  17  may also be configured to determine the force acting on the electrode  28 . Force acting on the electrode may be determined by, for example, multiplying the acceleration of the electrode  28  by the mass of the electrode  28 , or by referencing a look-up table. In an embodiment, system  10  may include a plurality of accelerometers  30  coupled to electrode  28 . Receiver  17  may be configured to receive respective acceleration signals from each of the accelerometers  30 , and to determine a vector representative of the magnitude and direction of the acceleration of electrode  28 . Receiver  17  may be further configured to determine a corresponding force vector acting on the electrode  28 . The receiver may be a standalone unit, as illustrated in  FIG. 1 . Receiver may also be incorporated with another piece of equipment, such as controller  14 , EnSite NavX system  15 , etc. 
         [0030]    Accelerometer  30  may be any type of accelerometer  30  and may further take many different forms. By way of example, and not of limitation, accelerometer may be a piezoelectric sensor, a piezoresistive sensor, a capacitive sensor, an electromechanical sensor, a micro-electromechanical system, a nano-electromechanical system, a low impedance output field effect transistor, a strain-gauge, a magnetic induction sensor, an L-C tank sensor, an optical sensor, a laser sensor, or combinations thereof. 
         [0031]      FIG. 2  is a partial section view of a shaft  222  of a catheter  212 , according to an embodiment. Catheter  212  may be similar to catheter  12  illustrated in  FIG. 1 . An electrode  228  is coupled to a distal end  226  of catheter shaft  222 . An accelerometer  230  (not illustrated) may be coupled to a proximal end of electrode  228 . When forces act on electrode  228 , and electrode  228  is displaced, accelerometer  230  is similarly displaced. When displaced, accelerometer  230  may be configured to provide a signal indicative of the acceleration of electrode  228  to a receiver, such as receiver  17  (best shown in  FIG. 1 ). The receiver  17  may be configured to receive the acceleration signals, and to determine at least one of the magnitude and direction of the acceleration of electrode  228 . Accelerometer  230  may transmit signals to receiver  17  along a wire, such as wire  229 . 
         [0032]      FIG. 3  is a partial perspective view of an electrode  328 , which may be similar to electrode  228  illustrated in  FIG. 2 . Electrode  328  is coupled to the distal end  326  of the shaft  322  of a catheter. Electrode  328  includes a proximal portion  334  defining a lumen  350 . Lumen  350  may be centered about an axis A′ defined through the center of electrode  328 . One or more accelerometers  330  may be coupled to electrode  328 . For example, in the illustrated embodiment, three accelerometers  330  are coupled to the electrode  328  along proximal portion  334 . The three accelerometers  330  may be equally spaced circumferentially around axis A′ defined through the center of lumen  350  and may all be positioned approximately the same radial distance from axis A. Accelerometers  330  may each be configured to provide a respective acceleration signal to a receiver, such as receiver  17 , when electrode  328  is subjected to an external force. An external force may be, for example, force from a beating heart with which an electrode  328  is in contact. Receiver  17  may be configured to receive the acceleration signals from accelerometers  330 , and to determine a vector representative of the acceleration of electrode  328 . As described previously, receiver  17  may further be configured to determine forces acting on electrode  328 , and to determine whether electrode  328  is in contact with tissue. 
         [0033]      FIG. 4  is a partial perspective view of an alternate embodiment of the invention, designated catheter  412 . Catheter  412  includes an electrode  428 . Electrode  428  is coupled to the distal end of a support structure  440 . Support structure  440  is housed within a distal end  426  of a catheter  412 . Distal end  426  of catheter  412 , which may include the portions of catheter  412  distal of line T, may be more flexible than the rest of catheter  412 , allowing for greater mobility of electrode  428 . 
         [0034]    The support structure  440  includes a distal base  442  having a outer surface  444  to which electrode  428  is coupled. Support structure  440  further includes a plurality of proximally directed protrusions  446 . Protrusions  446  are anchored to shaft  422  of catheter  412 . In an embodiment, protrusions  446  may traverse flexible distal end  426  and may be anchored to shaft  422  at a point proximal to line T. Protrusions  446  may be equally spaced circumferentially about support structure  440 . One or more accelerometers  430  may be coupled to one or more of protrusions  446 . In the illustrated embodiment, three accelerometers  430  may be included, each coupled to a respective protrusion  446 . 
         [0035]    When a force is applied to electrode  428 , such as the force of a beating heart, electrode  428  is displaced. The displacement of electrode  428  may be resolved across the support structure  440 , causing a respective dynamic strain to be produced in one or more of the protrusions  446 . Each accelerometers  430  coupled to a respective protrusions  446  generates an acceleration signal in response to the strain. Acceleration signals may then be transmitted from the one or more accelerometers  430  to a receiver, such as receiver  17 , along wires  429 . Received acceleration signals may then be used to determine the magnitude and/or direction of acceleration and/or orientation of electrode  428 . Received signals may also be used to determine the force acting on electrode  428 , and may be used to determine whether electrode  428  is in contact with an external body, such as a heart wall. 
         [0036]    Protrusions  446  of  FIG. 4  are generally illustrated as forming a tripod structure, and generally have an elongated shape. Protrusions may take any of a myriad of shapes, including a C-shape, a laterally inverted C-shape, a U-Shape, an inverted U-shape, an Omega (Ω) shape, an inverted Omega shape, an L-shape, a coil shape, a transversely aligned coil, or any other suitable shape. 
         [0037]      FIG. 5A  is a partial perspective view, with portions broken away, of a further catheter embodiment of the invention, designated catheter  512 , which includes an electrode  528 . A support structure  540  includes a cylindrical base  548 . A diaphragm  550  extends across at least a portion of an aperture defined by cylindrical base  548 , and is coupled to base  548  at various locations. A lever  552  is positioned along an axis A″ defined through the center of support structure  540 . A proximal end of lever  552  may be coupled to a proximal face  553  (See  FIG. 5B ) of diaphragm  550 . A distal end of lever  552  is coupled to electrode  528 . One or more accelerometers  530  may be coupled to an outer face  555  of diaphragm  550 . 
         [0038]    Cylindrical base  548  may be configured to be coupled to a shaft of catheter  512 . For example, base  548  may be coupled to shaft  522  at a point proximal to line T′. A proximal end of electrode  528  may be coupled to flexible distal end  522  of catheter  512 . If a force is applied to electrode  528 , electrode  528  may be displaced, causing a corresponding strain on diaphragm  550 . Accelerometers  530  may detect the strain on diaphragm  550  and generate signals in response thereto. Signals may be transmitted to a receiver, such as receiver  17 , along wires  529 . Receiver  17  may process the received signals and determine acceleration of electrode  528 , as well as forces acting on electrode  528 . This information may then be used to determine electrode contact with tissue. 
         [0039]      FIG. 5B  is a partial cross-sectional view of electrode  528  and support structure  540  of  FIG. 5A  taken substantially along line  5 B- 5 B. Lever  552  is coupled to electrode  528  at a proximal end  560 , and to a proximal face  553  of diaphragm  550  at a distal end  562 . Diaphragm  550  extends across a distal end of cylindrical base  548  of support structure  540 . Lever  552  is configured to interact with electrode  528  and with proximal face  553  of diaphragm  550 , such that displacement of electrode  528  causes lever  552  to create a force against proximal face  553  of diaphragm  550 . A plurality of accelerometers  530  are positioned along a distal face  555  of diaphragm  550 . Lever  552  is thus configured to transfer forces applied to electrode  528  to diaphragm  550 , where they are detected by accelerometers  530 . 
         [0040]      FIG. 6  is a schematic and block diagram overview of an embodiment of a system  610 . The system  610  includes a receiver  617  that is responsive to output signals provided by accelerometers  631 ,  632 ,  633 , which are configured to detect acceleration of an electrode  628 . Receiver  617  includes, among other things, a processor  645  that is configured to process the received signals in a manner described below to produce one or more parameters of interest, such as acceleration, applied force, degree of electrode-to-tissue contact, and the like. The receiver may be further configured to display information, such as the computed parameters of interest, to a user, such as an electrophysiologist, on a display  650 . 
         [0041]    Accelerometers  631 ,  632 ,  633  are coupled to electrode  628 . A force F is applied to electrode  628  causing electrode  628  to move. The movement of electrode  628  causes accelerometers  631 ,  632 ,  633  to sense acceleration and to output respective acceleration signals AS 1 , AS 2 , AS 3 . Signals AS 1 , AS 2 , AS 3  are received by a receiver  617  at inputs  641 ,  642 ,  643 . Inputs  641 ,  642 ,  643  are configured to receive acceleration signals AS 1 , AS 2 , AS 3  and to provide the signals AS 1 , AS 2 , AS 3  to a processor  645 . 
         [0042]    Processor  645  may include hardware and/or software configured to receive the acceleration signals AS 1 , AS 2 , AS 3 , and to process the signals AS 1 , AS 2 , AS 3  to determine one or more of an acceleration vector, force associated with one or more of the acceleration signals AS 1 , AS 2 , AS 3 , a force vector, and whether there is contact between the electrode and a surface, such as a wall of a beating heart. Processor  645  may determine the force acting on electrode  628  by multiplying acceleration values by the mass of electrode  628 . Additionally, or alternatively, processor  645  may determine force directly from the sensed acceleration signals using a lookup table or other mechanism. Contact may be determined by analyzing the forces applied to electrode  628 . For example, contact with a beating heart may be characterized by repeated acceleration in a first direction followed by acceleration in a second direction. The second direction may be opposite the first direction. 
         [0043]    Receiver  617  may be configured to output resultant values, such as acceleration value OS 1 , Force value OS 2 , and contact value OS 3 , to one or more user interface devices, such as a display screen  650 . Display screen  650  may be a dedicated screen for providing indications related to receiver outputs OS 1 , OS 2 , OS 3 . Display  650  may also be incorporated into one or more other devices such as an EnSite NavX™ Navigation and Visualization System. 
         [0044]    Acceleration signals, such as signals AS 1 , AS 2 , AS 3 , may be used alone or in conjunction with one or more other signals, such as signals from force sensors, temperature sensors, etc., to aid in electrophysiological procedures. For example, using acceleration signals in conjunction with force signals may allow detection of both static and dynamic forces. Acceleration signals may be used, in part, to determine tilt, direction, orientation, or other directional attributes of electrode  28 , and may assist in providing a clear picture of electrode  28  interaction with an associated treatment area. Signals may also be used in conjunction with one or more visualization systems to provide a more complete view of a treatment area, such as a cardiac chamber, as well as the position of an electrode, such as electrode  28 , relative to the treatment area. 
         [0045]    Acceleration signals may be used to determine local health of cardiac tissue, such as by determining the force with which cardiac muscle displaces an electrode  28  in contact therewith. Additionally, signals used to determine contact with tissue may, for example, increase the safety of ablation procedures by ensuring ablation energy is provided to an electrode only when the electrode is in contact with tissue. 
         [0046]    In addition to the foregoing, embodiment of the present invention may include catheters including additional features. For example, the present teachings may be included in an irrigated catheter. 
         [0047]    Although embodiments of this invention have been described above with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this invention. All directional references (e.g., upper, lower, upward, downward, left, right, leftward, rightward, top, bottom, above, below, vertical, horizontal, clockwise, and counterclockwise) are only used for identification purposes to aid the reader&#39;s understanding of the present invention, and do not create limitations, particularly as to the position, orientation, or use of the invention. Joinder references (e.g., attached, coupled, connected, and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the spirit of the invention as defined in the appended claims.