Endocardial mapping system

Abstract

A system for mapping electrical activity of a patient's heart includes a set of electrodes spaced from the heart wall and a set of electrodes in contact with the heart wall. Voltage measurements from the electrodes are used to generate three-dimensional and two-dimensional maps of the electrical activity of the heart.

Description

LaPlace's equation can be solved numerically or analytically. Such numerical techniques include boundary element analysis and other interative approaches comprised of estimating sums of nonlinear coefficients.

Specific analytical approaches can be developed based on the shape of the probe (i.e. spherical, prolate spherical or cylindrical). From electrostatic field theory, the general spherical harmonic series solution for potential is: $\varphi \left(r,\theta ,\phi \right)=\sum _{\infty }^{i-0}\sum _{m=-1}^l\left\{A_1{r}^1+B_1{r}^{-\left(i-1\right)}\right\}{\varphi }_{\mathrm{Im}}{Y}_{\mathrm{Im}}\left(\theta ,\phi \right)$

In spherical harmonics, Y_lm(θ, ψ) is the spherical harmonic series made up of Legendre Polynomials. Φ_lm is the lm^th component of potential and is defined as:
φ_lm=∫V(θ, ψ)Y_lm(θ, ψ)dΩ
where V(θ, φ) is the measured potential over the probe radius R and dΩ is the differential solid angle and, in spherical coordinates, is defined as:
dΩ=sin θdθdψ

During the first step in the algorithmic determination of the 3D map of the electrical activity each Φlm component is determined by integrating the potential at a given point with the spherical harmonic at that point with respect to the solid angle element subtended from the origin to that point. This is an important aspect of the 3D map; its accuracy in creating the 3D map is increased with increased numbers of electrodes in the array and with increased size of the spherical array. In practice it is necessary to compute the Φ_lm components with the subscript set to 4 or greater. These Φ_lm components are stored in an 1 by m array for later determination of potentials anywhere in the volume within the endocardial walls.

The bracketed expression of equation 1 (in terms of A₁, B₁, and r) simply contains the extrapolation coefficients that weight the measured probe components to obtain the potential components anywhere in the cavity. Once again, the weighted components are summed to obtain the actual potentials. Given that the potential is known on the probe boundary, and given that the probe boundary is non-conductive, we can determine the coefficients A₁ and B₁, yielding the following final solution for potential at any point within the boundaries of the cavity, using a spherical probe of radius R: $\varphi \left(r,\theta ,\phi \right)=\sum _{l=0}^{\infty }\sum _{m=-1}^l\left[\left(\frac{l+1}{2l+1}\right){\left(\frac{r}{R}\right)}^1+\left(\frac{l}{2l+1}\right){\left(\frac{r}{R}\right)}^{-i-1}\right]{\varphi }_{\mathrm{Im}}{Y}_{\mathrm{Im}}\left(\theta ,\phi \right)$

on exemplary method for evaluating the integral for Φ_lm is the technique of Filon integration with an estimating sum, discretized by p latitudinal rows and q longitudinal columns of electrodes on the spherical probe. ${\varphi }_{\mathrm{Im}}\ge \frac{4\pi }{\mathrm{pq}}\sum _{i=1}^p\sum _{j=1}^{q}V\left({\theta }_i,{\phi }_j\right)Y_{\mathrm{Im}}\left({\theta }_i,{\phi }_j\right)$
Note that p times q equals the total number of electrodes on the spherical probe array. The angle θ ranges from zero to π radians and ψ ranges from zero to 2π radians.

At this point the determination of the geometry of the endocardial walls enters into the algorithm. The potential of each point on the endocardial wall can now be computed by defining them as r, θ, and ψ. During the activation sequence the graphical representation of the electrical activity on the endocardial surface can be slowed down by 30 to 40 times to present a picture of the ventricular cavity within a time frame useful for human viewing.

A geometric description of the heart structure is required in order for the algorithm to account for the inherent effect of spatial averaging within the medium (blood). Spatial averaging is a function of both the conductive nature of the medium as well as the physical dimensions of the medium.

Given the above computed three-dimensional endocardial potential map, the intramural activation map of FIG. 11 is estimated by interpolating between the accurately computed endocardial potentials at locations 23 and 25 (FIG. 7), and actual recorded endocardial value at the surface electrode 24 and an actual recorded intramural value at the subsurface electrode 26 site. This first-order estimation of the myocardial activation map assumes that the medium is homogenous and that the medium contains no charge sources. This myocardial activation estimation is limited by the fact that the myocardial medium is not homogeneous and that there are charge sources contained within the myocardial medium. If more than one intramural point was sampled the underlying map of intramural electrical activity could be improved by interpolating between the endocardial surface values and all the sample intramural values. The center-of-gravity calculations can be summarized by the equation: $V\left(\stackrel{\_}{r_x}\right)=\frac{\sum _{i=1}^n{V}_i\left(|\stackrel{\_}{r_x}-\stackrel{\_}{r_i}{|}^{-k}\right)}{\sum _{i=1}^n|\stackrel{\_}{r_x}-\stackrel{\_}{r_i}{|}^{-k}}$
where, V(_x) represents the potential at any desired point defined by the three-dimensional vector _x and, V_i represents each of n known potentials at a point defined by the three-dimensional vector _i and, k is an exponent that matches the physical behavior of the tissue medium.

From the foregoing description, it will be apparent that the method for determining a continuous map of the electrical activity of the endocardial surface of the present invention has a number of advantages, some of which have been described above and others of which are inherent in the invention. Also modifications can be made to the mapping probe without departing from the teachings of the present invention. Accordingly the scope of the invention is only to be limited as necessitated by the accompanying claims.

Claims

1. An endocardial mapping catheter assembly comprising:

(a) a plurality of insulated wires braided throughout their length into an interlocking weave;

(b) a distal portion of the interlocking weave being expandable from a first generally cylindrical shape to a second expanded shape; and

(c) a plurality of electrodes on the distal portion of the insulated wires, each electrode in electrical communication with a single wire, and with each wire being in electrical communication with no more than a single electrode.

2. The endocardial mapping catheter assembly of claim 1, further comprising

d) an electrical plug on the proximal end of the interlocking weave, the electrical plug having a plurality of connections, each in electrical communication through one of the insulated wires to one of the electrodes.

3. The endocardial mapping catheter assembly of claim 1, wherein the interlocking weave further comprises a proximal non-expanding portion having a generally cylindrical shape.

4. The endocardial mapping catheter assembly of claim 3, wherein the proximal non-expanding portion is encapsulated in a biocompatible material.

5. The endocardial mapping catheter assembly of claim 4 wherein the biocompatible material is polyurethane.

6. The endocardial mapping catheter assembly of claim 4 wherein the distal expanding portion is not encapsulated in the biocompatible material.

7. The endocardial mapping catheter assembly of claim 1 wherein the second expanded shape is generally spherical.

8. The endocardial mapping catheter assembly of claim 1 wherein there are at least twenty-four electrodes.

9. The endocardial mapping catheter assembly of claim 1 further comprising an expandable balloon within the expandable distal portion of the wires.

10. An endocardial mapping catheter assembly comprising

(a) an elongated flexible lead body having an interior lumen and proximal and distal ends;

(b) at least twenty-four insulated wires in the lumen extending from the proximal to the distal end of the lead body, the wires collectively being braided together to form a wire assembly;

(c) an expandable portion of the wire assembly near the distal end of the flexible lead body, the expandable portion being expandable from a first generally cylindrical shape to a second expanded shape;

(d) the majority of wires in the wire assembly each having a single electrode in the expandable portion of the wire assembly;

(e) an electrical plug on the proximal end of the flexible lead body, the electrical plug having a plurality of connections, each connection being in electrical communication with one of the wires.

11. An endocardial mapping catheter assembly comprising:

(a) a plurality of insulated wires surrounded by an insulating material,

(b) a braid comprised of a combination of the insulated wires in an interlocking weave,

(c) a flexible material surrounding a first portion of the braid, forming a flexible lead body, the flexible material not surrounding a second portion of the braid, the second portion of the braid forming an array, the array being deformable into a predictable geometric shape,

(d) at least twenty-four electrodes on the braided wire array, each electrode in electronic communication with a single wire in the array.

12. The catheter assembly of claim 11 wherein the electrode is a gap in the insulating material surrounding the wire.

13. The catheter assembly of claim 11, wherein the flexible material is polyurethane.

14. The catheter assembly of claim 11, further comprising

e) an expandable balloon within the array.

15. The catheter assembly of claim 11, wherein the braid forms a lumen.

16. The catheter assembly of claim 15 further comprising a reference catheter in the lumen, the reference catheter having a tip electrode.

17. The catheter assembly of claim 16 wherein the reference catheter is movable relative to the braid within the lumen.

18. The catheter assembly of claim 17, further comprising

e) an electrical connector adapted for connection to an external monitoring device, the tip electrode of the reference catheter as well as each wire in the braid having an electrode being in electrical communication with a particular location on the electrical connector.

19. The catheter assembly of claim 11, further comprising

e) an electrical connector adapted for connection to an external monitoring device, each wire in the braid having an electrode being in electrical communication with a particular location on the electrical connector.