Abstract:
A method and apparatus are provided for assessing the degree of electrical signal blockage, or transmurality, of a line of ablation in which at least a first electrode adapted to deliver an electrical impulse is located on the first or one side of a line of ablation; and at least a second and a third electrode adapted to detect an electrical impulse are located on the second side of the line of ablation generally opposite to the first electrode. Each electrode may also be made up of more than one electrode, such as an electrode pair, to better assure reliability and tissue contact. Once the electrodes are located in contact with the tissue in question, an electrical impulse is delivered to the target tissue by the first electrode and detected by the second and third electrodes. Depending upon whether the line of ablation allows passage of electrical pulses, the second and third electrodes will detect the electrical impulse sequentially, with the order and/or timing of detection depending upon whether the electrical signal is able to directly cross the line of ablation or has to travel around the line of ablation to reach the second and third electrodes.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of the filing date of U.S. provisional patent application Ser. No. 61/121,586 filed Dec. 11, 2008, the entire contents of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Methods and apparatus have been developed for treating atrial fibrillation by creating lines of ablation or scar tissue that are intended to pose an interruption in the path of errant electrical impulses in the heart tissue. Scar tissue may be created by, e.g., surgical cutting of the tissue, freezing of the tissue by cryogenic probe, heating the tissue via RF energy and other technologies. Methods and apparatus for creating transmural lines of scar tissue or ablation using RF energy are shown and described in, e.g., U.S. Pat. No. 6,517,536, U.S. Pat. No. 6,974,454, and U.S. Pat. No. 7,393,353, which are incorporated herein by reference. The effectiveness of the ablation line at interrupting transmission of electrical signals is often associated, at least in part, with the transmurality of the line of ablation or scar tissue. Complete transmurality (fully through the thickness of the tissue) provides the most effective barrier. Partial or insufficient transmurality can allow undesired passage of aberrant electrical pulses. 
         [0003]    Various methods for determining the efficacy of the lines of ablation have been developed using pacing and sensing electrodes. For example, U.S. Pat. No. 6,905,498, also incorporated herein by reference, discloses an RF ablation clamp in which the jaws of the clamp have a pacing electrode positioned so as to be on one side of a line of ablation formed by the instrument and a sensing or EKG electrode positioned on a jaw on the opposite side of the line of ablation. Accordingly, if a pacing pulse or signal is applied to cardiac tissue on one side of the line of ablation, but not sufficiently detected by the EKG sensor on the other side of the line of ablation, the line of ablation may be deemed effective for blocking the errant electrical impulses associated with atrial fibrillation. 
       SUMMARY 
       [0004]    The present application discloses a method and apparatus for determining the efficacy of a lesion for blocking electrical signals with the use of a plurality of electrodes. More specifically, a method is provided for assessing the degree of electrical signal blockage, or transmurality, of a line of ablation in which at least a first electrode adapted to deliver an electrical impulse is located on the first or one side of a line of ablation. At least second and third electrodes adapted to detect an electrical impulse are located on the second side of the line of ablation generally opposite to the first electrode, with the second electrode being spaced from the line of ablation a first distance and the third electrode being spaced from the line of ablation a second distance greater than the first distance. Each electrode may also be made up of more than one electrode, such as an electrode pair, to better assure reliability and tissue contact. 
         [0005]    Once the electrodes are located in contact with the tissue in question, an electrical impulse is delivered to the target tissue by the first electrode (also called the pacing or stimulus electrode) and detected by the second and third electrodes (also called the EKG or sensing electrodes). Depending upon whether the line of ablation allows passage of electrical pulses, the second and third electrodes will detect the electrical impulse sequentially, with the order and/or timing of detection depending upon whether the electrical signal is able to directly cross the line of ablation or has to travel around the line of ablation to reach the second and third electrodes. Specifically, if the second electrode that is located closer to the line of ablation detects the electrical impulse prior to it being detected by the third electrode, then the line of ablation is not sufficiently transmural to block errant electrical impulses, as the electrical impulse has traveled directly across the line of ablation from the first electrode to the second electrode and then to the third electrode. On the other hand, if the third electrode detects the electrical impulse prior to it being detected by the second electrode, then the line of ablation is effective for directly blocking errant electrical impulses, as the electrical impulse has had to travel along or around the heart until it bypasses the ablation line to reach the second and third electrodes, and not through the line of ablation. 
         [0006]    In another aspect, a device is provided for performing the method. The illustrated device preferably comprises a deflectable, steerable end effector having at least first, second and third electrodes located thereon for contacting the tissue. The second and third electrode comprise a first group or array of electrodes, with the distance between the first electrode and the first group or array of electrodes (comprising the second and third electrodes) being sufficient to accommodate therebetween a line of ablation made in the tissue. The second and third electrodes are adapted for detecting an electrical impulse while the first electrode is adapted for delivering an electrical impulse. Preferably, an analyzer with associated display or user interface is provided for determining and providing an indication of the activation sequence and or timing of the second and third electrodes in response to an electrical impulse delivered by the first electrode. 
         [0007]    In a further aspect, a fourth electrode is provided adjacent the first electrode such that the first and fourth electrodes comprise a second group or array of electrodes. The first group or array of electrodes is spaced from the second group or array of electrodes a distance sufficient to accommodate therebetween the line ablation in the tissue. In this embodiment, the electrodes in each group are selectively either electrodes adapted for detecting electrical impulse or electrodes adapted for delivering an electrical impulse. Once again, an analyzer with an associated display or user interface is provided that is adapted to determine and provide an indication of the activation sequence of the electrodes in the group that is adapted for detecting the electrical impulse delivered by at least one of the electrodes in the group that is adapted to deliver an electrical impulse. By means of this embodiment, the efficacy of a lesion may be tested bi-directionally (i.e., with either group of electrodes being used for delivering or detecting electrical impulses), without the need to relocate or reposition the end effector. 
         [0008]    In a preferred embodiment, each electrode comprises a pair of closely-spaced electrodes. In a specific embodiment, each electrode has a width of approximately 1 mm, with the electrodes in each pair being spaced approximately 1.5 mm. The pair of electrodes in each group are spaced approximately 10 mm apart, while the first group of electrodes are spaced approximately 15 mm from the second group of electrodes. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a plan view of and exemplary device in accordance with the present disclosure. 
           [0010]      FIG. 2  is an enlarged view of the end effector of the device of  FIG. 1 , showing one embodiment of an electrode configuration in accordance with the present disclosure. 
           [0011]      FIG. 3  is a schematic view of a system including a device such as that illustrated in  FIGS. 1 and 2  and an associated analyzer. 
           [0012]      FIG. 4  is a schematic diagram of a switching circuit that may be used with the disclosed device. 
           [0013]      FIG. 5  is a schematic depiction of the use of a device in accordance with the present disclosure to determine the efficacy (i.e., the transmurality) of a lesion made in heart tissue. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    In accordance with the present disclosure, a method and a device are provided for determining the efficacy of a lesion for blocking electrical impulses. The method and device preferably utilizes at least three electrodes (and preferably at least three pairs of closely-spaced electrodes) to determine the efficacy of a lesion. This is done by locating one of the electrodes (or electrode pairs) on one side of the lesion and the other two electrodes (or electrode pairs) on the other side of the lesion and using the time it takes for an electrical impulse generated by the one electrode to be detected by the other two electrodes to provide an indication of the efficacy of the lesion for blocking electrical impulses. The sequence and/or timing of activation of the second and third electrodes indicates the direction the electrical impulse has had to travel—either directly across the line of ablation (if the lesion is not sufficiently transmural) or in generally the opposite direction around the heart (if the lesion is sufficiently transmural). 
         [0015]    Turning to  FIG. 1 , there is seen a device, generally indicated  10 , in accordance with the present disclosure. The device  10  includes a handle  12  to which is mounted an elongated shaft  14  having an end effector  16  at or near its distal end. In one example, the shaft  14  has an overall length of approximately 33 cm, with the proximal 25 cm preferably being rigid and the distal 7.5 cm comprising a deflectable section. The shaft may include a rigid portion  18  that comprises stainless steel or other material that is provided with an insulative finish or coating applied to the surface, or with a separate insulative overcoating or tube. The proximal end of the rigid portion of the shaft is secured to the handle  12  by a nose cone  20 . The distal flexible or deflectable section  16  may be made of any suitable material, such as a polymer or other elastomer such as a thermoplastic elastomer, and, for example, a material such as Pebax brand block copolymer from Arkema Inc. of Philadelphia, Pa. 
         [0016]    In one embodiment, the end effector  16  is sufficiently flexible so as to be capable of forming a two-inch diameter, 150° arc over its 7.5 cm of length, with the bending resistance preferably being substantially constant throughout the range of motion. The end effector  16  may be deflectable in any suitable manner and, as illustrated, is deflectable by means of a rotatable knob  22  on the handle  12  that may cooperate with one or more pull wires that extend through the shaft  14 , as is generally known in the art. Preferably, a two pull wire system is used for steering, with a first pull wire to control the radius of curvature of the end effector  16  and a second pull wire to pivot the end effector  16  with respect to a longitudinal axis. 
         [0017]    In one preferred embodiment, the end effector  16  is provided with four electrodes (or electrode pairs)  24 ,  26 ,  28 , and  30  for contacting the tissue to be tested. However, the number of electrodes (or electrode pairs) may be varied. While four electrodes are shown in the embodiment of  FIG. 1 , the method and device of the present disclosure may be practiced with as few as three electrodes (or electrode pairs). More than four electrodes (or electrode pairs) may also be used. If more than four electrodes (or electrode pairs) are used, the device may be able to test more than one lesion for transmurality without having to reposition the end effector to relocate the electrodes. Preferably, the deflectable portion of the end effector has markings or indicators of a suitable type at the locations of the electrodes that provide the user with a direct visual indication of the position of the electrodes relative to the line of ablation. 
         [0018]    With reference to  FIG. 2 , and as explained earlier, each electrode may be made up of a plurality of electrodes or electrical contact surfaces, such as a pair of electrodes or electrical surfaces, to better assure adequate tissue contact. Specifically, each electrode  24 ,  26 ,  28 ,  30  preferably comprises a pair of electrodes or electrical surfaces  24   a, b,    26   a, b,    28   a, b,  and  30   a, b.  Each electrode is preferably made of stainless steel with a polished finish and extends at least partially circumferentially about the end effector. As illustrated, the electrodes in each pair have a width of approximately 1 mm and are spaced approximately 1.5 mm from the other electrode in the pair. The electrode pairs comprise two arrays or groups  32 ,  34 , with each electrode pair in each group being spaced from the pair in the same group such that the adjacent electrodes are approximately 10 mm apart. Further, the first group or array of electrode pairs  32  is spaced from the second group or array of electrode pairs  34  so as to accommodate a line of ablation in the tissue between. In the illustrated embodiment, the spacing between the adjacent electrodes  26   b  and  28   a  in the two groups is approximately 15 mm. 
         [0019]    A control may be provided on the handle  12  for selecting which group of electrodes  32  or  34  will serve as the sending or pacing electrodes and as the receiving or EKG electrodes. The control may take the form of a rocker, toggle or slide switch  36  that may be thumb actuated. As illustrated, power is delivered to the pacing electrodes through a cord  38 , which also houses the electrical conductors for transmitting the signals received by the EKG electrodes to an analyzer (seen in  FIGS. 3 and 5 ). The analyzer determines the sequence and/or timing of activation of the EKG electrodes and provides an indication, preferably though a visual display, of the sequence or timing of activation, and may be either a separate unit into which the cord  38  is plugged or contained within the handle  12  and use a propriety software algorithm to determine directionality. 
         [0020]    With reference to  FIG. 3 , the device  10  is shown in conjunction with a separate analyzer  40 . The analyzer  40  preferably comprises a circuit (shown schematically) that interprets the signals generated and measured by the electrodes, and provides a signal to the user indicating whether a lesion has been created that satisfactorily blocks electrical impulses. For example, the analyzer  40  may be provided with a green light-emitting diode  42  that is illuminated if the lesion is “good” (i.e., the lesion blocks pacing signals) and a red light-emitting diode  44  that is illuminated if the lesion is “poor” (i.e., the lesion does not adequately block pacing signals). Preferably, if the contact of the electrodes to the epicardial surface of the heart is inadequate (i.e., not sufficiently conductive), neither diode will be illuminated. As can be appreciated, other types of signals, audible as well as visual, may be provided. 
         [0021]    Returning to  FIG. 3 , a micro-controller  46  is provided that triggers a pacing or stimulus pulse from one electrode or electrode pair, and measures the arrival times of the reflex waves at the second and third electrodes or electrode pairs. As illustrated, the electrocardial signals are amplified by instrument amplifiers  48 ,  50 . The resulting signals are then conditioned by band pass filters  52 ,  54  to remove interfering low frequencies, like power line hum, and interfering high frequencies like radio frequency noise. Thus, only signals containing valid EKG information are measured. The signals are then differentiated at  56 ,  58  to remove any DC offset and to produce sharp pulses for input to the micro-controller  46 . 
         [0022]    As shown, the stimulus/pacing generator  60  and power supply  62  are separate from the hand piece. Optionally, the stimulus/pacing generator and power supply may be incorporated into the hand piece, in which case the entire system becomes self-contained, and no connecting wires or cables or external power source are necessary. Under such circumstances, the power supply may be a non-replaceable battery that is connected to the system when, e.g., a tab is pulled, thus limiting the use of the device to a single surgical procedure. 
         [0023]    With reference to  FIG. 4 , a switching circuit  66  is shown that switches the four electrode pairs between six pairs of connecting wires  68 ,  70 ,  72 ,  74 ,  76 ,  78 . The device  10  is capable of switching between the proximal electrodes and distal electrodes for the delivery of pacing signals, and, switching between the distal and proximal electrode pairs  32 ,  34  for the sensing of signals, by manipulating the switch  36  on the hand piece  12 . Thus, the device may be operated without the necessity of disconnecting and reconnecting the wires from the electrodes to the analyzer. 
         [0024]    Specifically, the circuit  66  includes a first switch  80  connected to the stimulus or pacing generator and selectively connecting either the proximal pair  30   a,    30   b  or distal pair  24   a,    24   b  of the electrodes thereto. A second switch  82  connects a first EKG channel to one of the two inner pairs of electrodes  26   a, b  or  28   a, b,  and a third switch  84  selectively connects a second EKG channel to one of the proximal and distal pairs of electrodes  24   a, b  or  30   a, b.  Operation of the three switches is simultaneous such that the electrodes connected to the pacing generator will be in one of the groups  32 ,  34  of electrodes and the two electrodes connected to the EKG channels will be in the other group of electrodes. By using the switch  36 , the user will develop an intuitive feel for whether the pacing pulses are being applied to the distal or proximal electrodes, making a visual indication of such status unnecessary. 
         [0025]    As an alternative, the switching circuit can be modified to provide for three pairs of sensing electrodes to be used in combination with either a single pair of pacing electrodes or an entirely separate and self-contained pacing device. The use of the third pair of sensing electrodes allows for the determination of the angle at which the pacing impulse is received. Specifically, the use of two sensing points indicates which one of two directions an electrical impulse is moving. The addition of the third sensing point, with the relative positions of the sensing points being fixed and the appropriate sensing equipment to measure the timing, allows the determination of the angle at which the electrical impulse is passing the sensing points. 
         [0026]    One particular use of a device such as that described above to determine the efficacy of a lesion is shown in  FIG. 5 . Although illustrated with respect to heart tissue, other types of tissues could also be tested using the described apparatus and method.  FIG. 5  depicts a human heart  90  in which a series of ablation lines have been made as part of the “Maze” procedure for treating atrial fibrillation. Lesions  92  and  94 , respectively, separately encircle the left and right pulmonary veins. Lesion  96 , called the “roof line lesion,” connects the lesions  92  and  94 , while a lesion  98 , called the “trigone lesion,” extends between the mitral valve annulus and the roof line lesion  96 . 
         [0027]    A device having an end effector  16  in accordance with the present disclosure is provided. The end effector  16  shown in  FIG. 3  comprises four electrodes, each made up of a pair of electrodes, with electrode pairs  24   a, b  and  26   a, b  comprising the first array or group of electrodes and electrodes  28   a, b  and  30   a, b  comprising the second array or group of electrodes. The end effector  16  is brought into contact with the surface of the heart  90 , with the first and second group of electrodes straddling the trigone lesion  98 . To test the lesion in a first direction, the electrode pair  24   a, b  in the first group is switched so as to be connected to a pacing pulse generator  60 , while the electrode pairs  28   a, b  and  30   a, b  serve as the EKG electrodes and are connected to the analyzer  40 . 
         [0028]    A pacing pulse is delivered to the heart  90  through the electrodes  24   a, b.  If the trigone lesion  98  is sufficiently effective to block electrical signals (i.e., transmural), the pacing pulse cannot cross and, in order to be detected by the EKG electrodes, must travel around the back of the heart, where it would first be detected by electrode pair  30   a, b  and later by electrode pair  28   a, b.  The analyzer  40  determines the sequence of activation of the electrode pairs, and provides an indication thereof. If the sequence of activation is first electrode pair  30   a, b  and then the electrode pair  28   a, b,  the lesion  98  is deemed transmural. If the sequence of activation is first electrode pair  28   a, b  and then electrode pair  30   a, b,  the lesion is deemed to be not transmural or not sufficiently formed to block electrical signals. 
         [0029]    The lesion  98  may then be tested from the opposite direction without moving end effector in order to confirm the determination of transmurality. This may be accomplished by switching the device so that electrode pair  30   a, b  serves as the sending or pacing electrode, and the electrode pairs  24   a, b  and  26   a, b  serve as the receiving or EKG electrodes. Thus, the device may be used bi-directionally to test the transmurality of a lesion. 
         [0030]    After a first lesion is tested, the end effector may be manipulated so that the first and second groups  32 ,  34  of electrodes straddle a different lesion, and the testing of that lesion is conducted as set forth above. 
         [0031]    Thus, a method and apparatus for determining the efficacy of a lesion for blocking electrical signals. While the method and apparatus have been described in the context of certain preferred embodiments, there is no intent to limit this application to the same. Instead, the method and apparatus are to be defined by the following claims.