Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
2000-06-21
2002-06-04
Layno, Carl (Department: 3762)
Surgery
Diagnostic testing
Cardiovascular
Reexamination Certificate
active
06400981
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to invasive methods for mapping of organs in the body, and specifically to methods for mapping electrical activity in the heart.
BACKGROUND OF THE INVENTION
Cardiac mapping is used to locate aberrant electrical pathways and currents within the heart, as well as diagnosing mechanical and other aspects of cardiac activity. Various methods and devices have been described for mapping the heart. Exemplary methods and devices are described in U.S. Pat. Nos. 5,471,982 and 5,391,199 and in PCT patent publications WO94/06349, WO96/05768 and WO97/24981, whose disclosures are incorporated herein by reference. U.S. Pat. No. 5,391,199, for example, describes a catheter including both electrodes for sensing cardiac electrical activity and miniature coils for determining the position of the catheter relative to an externally-applied magnetic field. Using this catheter a cardiologist can collect data from a set of sampled points within a short period of time, by determining the electrical activity at a plurality of locations and determining the spatial coordinates of the locations.
Methods of creating a three-dimensional map of the heart based on these data are disclosed, for example, in European patent application EP 0 974 936 and in a corresponding U.S. patent application Ser. No. 09/122,137, which is assigned to the assignee of the present patent application, and whose disclosure is incorporated herein by reference. As indicated in these applications, position coordinates (and optionally electrical activity, as well) are initially measured at about 10 to 20 points on the interior surface of the heart. These data points are generally sufficient to generate a preliminary reconstruction or map of the cardiac surface to a satisfactory quality. The preliminary map is preferably combined with data taken at additional points in order to generate a more comprehensive map. In clinical settings, it is not uncommon to acquire data at 100 or more sites to generate a detailed, comprehensive map of heart chamber electrical activity.
In order to speed up the process of data acquisition, multiple-electrode catheters have been developed to simultaneously measure electrical activity at multiple points in the heart chamber. Such catheters are described, for example, in U.S. Pat. Nos. 5,487,391 and 5,848,972, whose disclosures are incorporated herein by reference. These catheters having multiple electrodes on a three-dimensional structure, which expands inside the heart to take the form of a basket. The basket structure is designed so that when deployed, its electrodes are held in intimate contact against the endocardial surface. A problem with the catheters disclosed in these patents is that they are both difficult and expensive to produce. The large number of electrodes in such catheters is also very demanding of the data recording and processing subsystem. There are additional complexities associated with the deployment and withdrawal of these catheters, and increased danger of coagulation.
U.S. Pat. No. 4,649,924, whose disclosure is likewise incorporated herein by reference, discloses a non-contact method for the detection of intracardiac electrical potential fields. A catheter having an inflatable distal end portion is provided with a series of sensor electrodes distributed over its surface and connected to insulated electrical conductors for connection to signal sensing and processing means. The size and shape of the end portion are such that the electrodes are spaced substantially away from the wall of the cardiac chamber. The sensor electrodes are preferably distributed on a series of circumferences of the distal end portion, lying in planes spaced from each other. These planes are perpendicular to the major axis of the end portion of the catheter.
PCT patent publication WO99/06112, whose disclosure is also incorporated herein by reference, describes an electrophysiological cardiac mapping system and method based on a non-contact, non-expanded multi-electrode catheter. The electrodes on the catheter are used to simultaneously measure the electrical potentials at multiple points on the catheter surface, inside the volume of the heart chamber. To generate the map, these electrical measurements are combined with a knowledge of the relative geometry of the probe and the endocardium. This geometrical knowledge must be obtained by an independent imaging modality, such as transesophogeal echocardiography. Based on the known geometry, Laplace's equation is solved to find a relation between the potential on the endocardial surface to that on the catheter, in the form of a matrix of coefficients. This matrix is inverted, so as to determine the endocardial potentials based on the electrode potentials. A regularization technique, such as a method of finite element approximation, must be used to ensure proper convergence of the solution.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved method for mapping electrical potentials inside a volume, and particularly on a surface bounding the volume.
It is a further object of some aspects of the present invention to provide an improved method for mapping endocardial electrical potentials.
It is still a further object of some aspects of the present invention to provide a method that enhances the speed with which a map of endocardial electrical potentials can be generated.
It is yet a further object of some aspects of the present invention to provide improved methods and apparatus for mapping electrical potentials in the heart while minimizing contact with the endocardium.
In preferred embodiments of the present invention, a mapping probe, preferably a catheter, is inserted into a chamber of the heart, and is used to generate a map of electrical activity over an endocardial surface of the chamber. The catheter comprises one or more position sensors in a distal portion of the catheter, along with a plurality of electrodes, which are distributed over the surface of the distal portion. A geometrical model of the endocardial surface is formed, preferably using the position-sensing capability of the catheter itself, as described, for example, in the above-mentioned U.S. patent application Ser. No. 09/122,137. Electrical potentials within the volume of the chamber are measured using the electrodes on the catheter surface, whose positions are known precisely due to the position sensors in the catheter. The measured potentials are combined with the geometrical model to generate a map of electrical potentials at the endocardial surface.
Preferably, the map is generated by modeling the electric field in the heart chamber as a superposition of fields generated by discrete electric dipoles distributed over the endocardial surface. In this manner, a set of equations is generated, expressing the potential at each of the points on the catheter as a sum of the dipole fields at that point. The set of equations is inverted to find the strengths of the dipoles on the endocardial surface, from which the activation potentials are then determined. The dipole model has been found to give accurate results, while avoiding the heavy computational burden of finite element approximations and other regularization techniques. Alternatively, however, other methods of computation may be used, such as those described in the above-mentioned PCT publication WO99/06112.
Preferably, the electrodes are distributed over the distal portion of the catheter in an array, most preferably a grid array, as described in a U.S. patent application Ser. No. 09/506,766, which is assigned to the assignee of the present patent application, and whose disclosure is incorporated herein by reference. Further preferably, the catheter comprises two position sensors, one near the distal tip of the catheter, and the other near the proximal end of the electrode array, as described in U.S. Pat. No. 6,063,022, which is also assigned to the assignee of the present patent application, whose disclosure is also incorporated herein b
Biosense Inc.
Capezzuto Louis J.
Layno Carl
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