Abstract:
A method of mapping ventricular arrhythmias in a subject includes placing a plurality of ECG leads on the subject; triggering an arrhythmia with a pacing catheter, determining its location and recording the resulting ECG signals from the plurality of leads; successively navigating the electrode on a catheter to each of a plurality of points in the general location of the source of the arrhythmia site, applying electrical stimulation to each site via the electrode, and recording the resulting paced ECG; and comparing each paced ECG from each point with an ECG during the arrhythmia to identify the point where the paced ECG most closely corresponds to the ECG during arrhythmia.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/701,226, filed Jul. 21, 2005, the entire disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to diagnosing and treating cardiac arrhythmias, and in particular to a method of finding the source of a cardiac arrhythmia and treating the arrhythmia.  
         [0003]     Cardiac arrhythmias are usually the result of errant electrical signals in the heart. There are several treatments for arrhythmias, including drugs, surgical procedures in which blocks to the errant electrical signals are made by making incisions in the heart tissue, and ablation procedures which attempt to destroy the source of the errant signals or block the paths of the errant signals. One of the difficulties of these ablation procedures is accurately identifying the source of the errant signals. A physician can manipulate the mapping catheter over the cardiac surfaces to sense the local electrical signals and try to identify the source of the signal. This can be a time consuming and tedious task. Remote navigations systems have made this somewhat better, by allowing for the automated mapping of selected cardiac surfaces. The remote navigation systems are usually mechanically- or magnetically-based. Mechanical-based remote navigation systems mechanically orient the distal end of a medical device inside the body using a mechanical system, such as a pull wires or gears, after which the distal end can be advanced by pushing the proximal end. Magnetic-based remote navigation systems magnetically orient the distal end of a medical device inside the body using one or more source magnets that project a magnetic field of changeable direction inside the subject, to orient one or more magnetically responsive elements on the medical device.  
       SUMMARY OF THE INVENTION  
       [0004]     Generally, the methods of the preferred embodiments of this invention facilitate the location of the source of errant signals causing cardiac arrhythmias. In accordance with a first preferred embodiment, the leads of a standard 12 lead ECG system are placed on the subject. The positions of the leads are identified in a reference frame. A pacing catheter is placed at a known location (the location is determined for instance through Fluoro localization of the catheter tip, or through the use of a location sensor placed at the catheter tip and connected to a localization system, etc.) and is used to induce an arrhythmia. The result is the identification of a source area on the surface of the heart by means of the ECG signals recorded by the 12 leads. The pacing catheter can then be traversed over the source area, preferably using a remote navigation system, and pacing at each of a plurality of locations in the source area. The ECG signals resulting from pacing at each location in source area is compared with the ECG signal from a spontaneous arrhythmia. The location from which pacing results in an ECG the same as or closest to the ECG from a spontaneous arrhythmia is the source of the arrhythmia.  
         [0005]     Once the source is identified, then the arrhythmia can be treated by either destroying the source, or by isolating the source. This can be conveniently done with the remote navigation system, which merely needs to return an ablation catheter (which can be the same as the pacing catheter) to the identified location. The tissue is ablated, and the arrhythmia eliminated. Alternatively, a line of ablation is formed around the source, blocking the conduction of the errant signals from the source. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a flow chart illustrating a preferred embodiment of the methods of this invention;  
         [0007]      FIG. 2  is a flow chart illustrating another preferred embodiment of the methods of this invention;  
         [0008]      FIG. 3  is a diagram showing the typical placement of the precordial leads of a 12 lead ECG;  
         [0009]      FIG. 4  is a diagram of a heart illustrating the calibration of the 12 lead ECG for localizing an arrhythmia;  
         [0010]      FIG. 5  is an example of an ECG showing a provoked arrhythmia which can be used to acquire the 12 lead vectors to localize the source of the arrhythmia;  
         [0011]      FIG. 6  is diagram of the heart showing an example the source location identified from the ECG signals, with a plurality of possible pacing points therein;  
         [0012]      FIG. 7  is a diagram of the heart showing resulting ECG signals from pacing from selected points within the identified source location;  
         [0013]      FIG. 8  is a schematic diagram illustrating the comparison between an ECG signal from pacing with an ECG signal of a spontaneous arrhythmia. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0014]     Embodiments of the methods of this invention provide for the mapping of arrhythmias, and in particular the localization of the source of arrhythmias. Once the source is located, the arrhythmia can be treated, either with direct ablation in which an ablation device is returned to the mapped location that is identified as the source of the arrhythmias, or by isolation, where conduction paths from the source are blocked by lines of ablation.  
         [0015]     One preferred embodiment is shown in  FIG. 1 . As shown in  FIG. 1 , at step  20  the leads for a conventional 12 lead ECG are placed on the subject. A typical arrangement for the precordial leads is shown in  FIG. 3 . At step  22  the ECG leads are localized in a single reference frame, so that the relative positions of the leads are known. This can be done by including a localization element in each lead which can be localized, for example with an RF localization system. Alternatively, a localizing wand having a localizing element can be temporarily touched to each lead to localize the lead, for example with an RF localization system. The leads were preferably localized in the same frame or reference as a remote navigation system, or in a frame of reference with known relationship to the remote navigation system. Thus the localization system may be provided in conjunction with a remote navigation system, in which case the leads are conveniently localized in a common reference frame with the localization system.  
         [0016]     After the leads are localized, the leads can be calibrated by pacing the heart at one or more landmark locations, as shown schematically in  FIG. 4 , and then trying to localize the signal from the known landmark location with the pacing leads. The result is a way to localize a signal source to a small area or region using the packing leads from the 12 lead ECG system.  
         [0017]     At step  24  an arrhythmia is stimulated with a pacing catheter. Alternatively, the subject could be monitored until an arrhythmia occurs naturally. The ECG signal corresponding to the arrhythmia is stored for later comparison, as described below. At step  26  the source location of the arrhythmia is located using the signals from the localized leads. The result, as illustrated in  FIG. 5  is a generally circular area  50  on the surface of the heart that probably includes the origin of the arrhythmia.  
         [0018]     The leads were preferably localized in the same frame or reference as a remote navigation system, or in a frame of reference with known relationship to the remote navigation system. The remote navigation system is preferably a mechanical or magnetic navigation system, although the methods could be implemented with any remote navigation system capable of remotely orienting the distal end of medical device, in response to the input of one or more control variables. Mechanical navigation systems typically employ a sleeve or collar for orienting the end of a medical device that telescopes there through. Mechanical elements such as push wires, pull wires, or other devices orient the sleeve or collar. One example of such a device is disclosed in U.S. patent application Ser. No. 10/378,547, filed Mar. 3, 2003, entitled Guide for Medical devices, which is a continuation of Ser. No. 09/875,279, filed Jun. 6, 2001, now U.S. Pat. No. 6,529,761, the disclosures of which are incorporated herein by reference. Magnetic navigation systems typically employ one or more external source magnets for creating a magnetic field in a selected direction which acts upon one or more magnetically responsive elements incorporated into the medical device to orient the distal end of the medical device. Such systems are presently available from Stereotaxis, Inc., St. Louis, Mo. Of course a remote navigation is not required to implement the present invention, and the pacing catheter could be manually moved, and localized with a localization system.  
         [0019]     A pacing device is navigated to the probable location  50  of the source of the arrhythmia, and at step  28  the pacing device is navigated to a particular point  52  in the area  50 . At step  30  the heart is paced from a particular point  52 . At  32  the ECG from the pacing is compared with the ECG recorded during an arrhythmia. If the two ECGs are substantially the same, then the point is most probably the origin of the arrhythmia. If the two ECG are not similar then at step  28  the pacing device is moved to another point. Steps  28 ,  20  and  32  are repeated until the closest match is found and than at  34  pacing stops.  FIG. 8  illustrates a comparison between the ECG signal  62  resulting from pacing at one of the points  52 , and the ECG signal  60  during arrhythmia. The smaller the area  64  between these two signals, to closer the corresponding pacing point  52  is to the origin of the arrhythmia. The location of a particular pacing point  52  is preferably already known to the remote navigation system or it could be determined using a localization system, and preferably the same localization system used to localize the ECG leads.  
         [0020]     Thereafter, as shown in  FIG. 1 , at  36  an ablation device (which can be the same as the pacing device) can be moved to the point corresponding to the arrhythmia source, and at  38  the tissue at the arrhythmia source is ablated.  
         [0021]     Alternatively, as shown in  FIG. 2  the steps  28  of moving the pacing catheter,  30  of pacing from the point; and  32  of measuring the ECG are continued until the entire source location has been pace-mapped.  FIG. 7  illustrates the differing ECG signals resulting from pacing at the various locations  52  in the area  50 . Then at  40  the best fit between the pace-mapped ECGs and the arrhythmia ECG is found, and the corresponding point identified as the arrhythmia site. One way of comparing these ECG signals is shown in  FIG. 8 , and described above, but any method for comparing these signals and identifying the closest signal form to the arrhythmia ECG can be used. The location of the particular point  52  in the area corresponding to the origin of the arrhythmia is already known to the remote navigation system, but could also be determined with any medical localization system,  
         [0022]     Thereafter, as shown in  FIG. 2 , at  36  an ablation device (which can be the same as the pacing device) can be moved to the point corresponding to the arrhythmia source, and at  38  the tissue at the arrhythmia source is ablated.  
         [0000]     Operation  
         [0023]     In operation, the ECG units are placed on the subject, and those leads are localized in a common reference frame (preferably the reference frame of a remote navigation system). An arrhythmia is triggered with a pacing catheter, and the signals from the plurality of leads and their known relative locations are used to determine a general location of the source of the arrhythmia.  
         [0024]     Alternatively the pacing catheter tip is localized using standard methods. The pacing device is successively navigated to a grid of points covering the location of the source of the arrhythmia, preferably using the remote navigation system. At each point a pacing signal is applied, and the paced ECG is recorded. After the source location has been pace-mapped in this manner, the resulting pace maps are compared with an ECG during an arrhythmia. The point corresponding to closest matching pace-map is identified as the source of the arrhythmia.  
         [0025]     Once the source is identified, it can be ablated or isolated to treat the arrhythmia. The remote navigation system can be used to return the pacing device to the identified point. The pacing catheter can then be used to ablate tissue to treat arrhythmia. The remote navigation system can be used to facilitate this navigation. Alternatively, a separate ablation catheter can be introduced and used to perform the ablation.