U.S. patent application number 09/999662 was filed with the patent office on 2002-05-16 for systems and methods for assessing stability of an operative instrument in a body region.
This patent application is currently assigned to EP Technologies, Inc.. Invention is credited to Panescu, Dorin, Swanson, David K., Whayne, James G..
Application Number | 20020058870 09/999662 |
Document ID | / |
Family ID | 28042118 |
Filed Date | 2002-05-16 |
United States Patent
Application |
20020058870 |
Kind Code |
A1 |
Panescu, Dorin ; et
al. |
May 16, 2002 |
Systems and methods for assessing stability of an operative
instrument in a body region
Abstract
A graphical user interface (GUI) is provided for assisting
medical personnel in interpreting data collected by a multiple
electrode catheter deployed within the body. The GUI generates and
displays an image of the multiple electrode catheter. By
manipulating appropriate controls, the medical personnel are able
to change the orientation of the displayed image until it matches
the orientation of the actual multiple electrode catheter as seen
on a fluoroscope. Afterwards, the medical personnel can determine
the relative position and orientation of the catheter by reference
to the GUI generated image. To aid in interpreting data recovered
by the catheter, the individual electrodes and splines are
highlighted and labeled. Electrodes recovering particular types of
physiological waveforms can be automatically identified and
highlighted. Comments and anatomic landmarks can be inserted where
desired to further assist in interpreting data. Views from various,
virtual fluoroangles can be obtained, and various images can be
recorded, stored and printed. The position of a roving electrode
can also be indicated.
Inventors: |
Panescu, Dorin; (San Jose,
CA) ; Swanson, David K.; (Mountain View, CA) ;
Whayne, James G.; (San Jose, CA) |
Correspondence
Address: |
LYON & LYON LLP
633 WEST FIFTH STREET
SUITE 4700
LOS ANGELES
CA
90071
US
|
Assignee: |
EP Technologies, Inc.
San Jose
CA
|
Family ID: |
28042118 |
Appl. No.: |
09/999662 |
Filed: |
October 31, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09999662 |
Oct 31, 2001 |
|
|
|
09403802 |
Mar 7, 2000 |
|
|
|
09403802 |
Mar 7, 2000 |
|
|
|
PCT/US98/05763 |
Mar 6, 1998 |
|
|
|
Current U.S.
Class: |
600/424 ;
600/374 |
Current CPC
Class: |
A61B 6/12 20130101; A61B
2560/045 20130101; A61B 2562/043 20130101; A61B 5/7435 20130101;
A61B 5/6858 20130101; A61B 5/287 20210101 |
Class at
Publication: |
600/424 ;
600/374 |
International
Class: |
A61B 005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 7, 1997 |
US |
08/813624 |
Claims
we claim:
1. A graphical user interface for generating a visual display
depicting the relative position and orientation of a multiple
electrode catheter within a body comprising: a display screen, an
image generator for generating on the display screen an image of
the multiple electrode catheter, and a user-actuable control
coupled to the image generator for changing the relative position
and orientation of the image as displayed on the display
screen.
2. A graphical user interface as defined in claim 1 wherein the
user-actuable control further operates to display the image from
one or more predetermined viewing angles.
3. A graphical user interface as defined in claim 1 wherein the
image generator highlights the electrodes on the displayed image of
the multiple electrode catheter.
4. A graphical user interface as defined in claim 1 wherein the
multiple electrode catheter includes a plurality of splines and the
image generator functions to highlight the splines of the displayed
image.
5. A graphical user interface as defined in claim 1 wherein the
image generator displays certain elements of the image at brighter
intensity than other elements of the image to enhance the
three-dimensional appearance of the displayed image.
6. A graphical user interface as defined in claim 1 wherein the
image generator further generates labels associated with individual
ones of the displayed electrodes.
7. A graphical user interface as defined in claim 1 wherein the
image generator further generates labels associated with individual
ones of the displayed splines.
8. A graphical user interface as defined in claim 1 wherein the
image generator further generates labels associated with a roving
electrode.
9. A graphical user interface as defined in claim 1 wherein the
image generator further generates anatomic markers representative
of anatomic features within the body.
10. A graphical user interface as defined in claim 1 wherein the
image generator further generates user-created markers
representative of preidentified events occurring during an
electrophysiological procedure.
11. A graphical user interface as defined in claim 1 wherein the
user-actuable control is operable to place the anatomic markers at
user-selected locations relative to the displayed image.
12. A graphical user interface as defined in claim 1 wherein the
image generator further operates to develop binary maps in response
to physiological data received by individual ones of the electrodes
of the multiple electrode catheter.
13. A graphical user interface as defined in claim 12 wherein the
binary maps are based on the detection of early activation
occurrences at one or more electrodes of the multiple electrode
catheter.
14. A graphical user interface as defined in claim 12 wherein the
binary maps are based on the detection of fractionation occurrences
at one ore more electrodes of the multiple electrode catheter.
15. A graphical user interface as defined in claim 12 wherein the
binary maps are based on the detection of good -pace occurrences at
one or more electrodes of the multiple electrode catheter.
16. A graphical user interface as defined in claim 12 wherein the
binary maps are based on the detection of concealed entrainment
occurrences at one or more electrodes of the multiple electrode
catheter.
17. A graphical user interface as defined in claim 1 wherein the
image generator further operates to develop iso-value maps in
response to physiological data received by individual ones of the
electrodes of the multiple electrode catheter.
18. A graphical user interface as defined in claim 1 wherein the
image generator displays the position of roving electrodes with
respect to the multiple electrode catheter.
19. A graphical user interface as defined in claim 1 wherein the
user-actuable control includes the keyboard of a computer.
20. A graphical user interface as defined in claim 1 wherein the
graphical user interface comprises a computer and a software
program operating on the computer.
21. A method of utilizing a multiple electrode structure within a
body comprising the steps of: locating the multiple electrode
structure within a body, displaying the actual multiple electrode
structure on an imaging screen, and generating and displaying on
another screen an image representing the multiple electrode
structure, changing the displayed orientation of the image until
the orientation of the displayed image substantially matches the
orientation of the actual multiple electrode structure as displayed
on the imaging screen.
22. A method as defined in claim 21 further comprising the steps
of: introducing a roving electrode into the body, and generating
and displaying an image representing the roving electrode on the
other screen.
23. A method as defined in claim 21 comprising the further step of
generating and displaying on the other screen binary maps
indicative of the presence or absence of predetermined
physiological events.
24. A method as defined in claim 23 comprising the further step of
generating two or more binary maps representative of the presence
or absence of two or more different predetermined physiological
events.
25. A method as defined in claim 24 comprising the further step of
identifying potential treatment sites by correlating the occurrence
of two or more different physiological events at single locations.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to Graphical User
Interfaces (GUIs) and, more particularly, to GUIs useful in
connection with positioning, orienting and operating a multiple
electrode catheter within a patient's body for diagnostic,
therapeutic or other purposes.
[0002] Multiple electrode catheters, such as those shown and
described in U.S. Pat. Nos. 5,595,183 and 5,487,391 commonly owned
by the assignee hereof, are useful in a variety of medical
diagnostic and therapeutic procedures. Such catheters are
particularly useful in diagnosing and treating certain cardiac
disorders, such as arrhythmias, that can occur for example when
localized areas of abnormal tissue within the heart disrupt the
normal sinus rhythm.
[0003] Today, physicians examine the propagation of electrical
impulses in heart tissue to locate aberrant conductive pathways.
The techniques used to analyze these pathways, commonly called
"mapping," identify regions in the heart tissue, called foci, which
can be ablated to treat the arrhythmia.
[0004] One form of conventional cardiac tissue mapping techniques
uses multiple electrodes positioned in contact with epicardial
heart tissue to obtain multiple electrograms. The physician
stimulates myocardial tissue by introducing pacing signals and
visually observes the morphologies of the electrograms recorded
during pacing. The physician visually compares the patterns of
paced electrograms to those previously recorded during an
arrhythmia episode to locate tissue regions appropriate for
ablation. These conventional mapping techniques require invasive
open heart surgical techniques to position the electrodes on the
epicardial surface of the heart.
[0005] Another form of conventional cardiac tissue mapping
technique, called pace mapping, uses a roving electrode in a heart
chamber for pacing the heart at various endocardial locations. In
searching for the VT foci, the physician must visually compare all
paced electrocardiograms (recorded by twelve lead body surface
electrocardiograms (ECG's)) to those previously recorded during an
induced VT. The physician must constantly relocate the roving
electrode to a new location to systematically map the
endocardium.
[0006] These techniques are complicated and time consuming. They
require repeated manipulation and movement of the pacing
electrodes. At the same time, they require the physician to
visually assimilate and interpret the electrocardiograms.
[0007] Multiple electrode catheters are effective in simplifying
cardiac mapping and ablation procedures. Such catheters make it
possible to simultaneously obtain data from several locations
within the heart or other organ using a single catheter. During
such procedures, the multiple electrode catheter is introduced into
a chamber of the heart using known, minimally invasive techniques.
The catheter's progress through the vein and into the heart can be
followed on a fluoroscope. Radiopaque markers on the catheter
enhance the fluoroscopic visibility of the catheter. Once proper
deployment within the heart is verified by the fluoroscopic image,
localized electrical activity within the heart is monitored by
means of the individual electrodes. By noting particular types and
patterns of abnormality in the sensed waveforms, the physician is
able to identify areas of abnormality in the heart tissue. The
abnormal tissues can then be ablated or otherwise treated to remedy
the condition.
[0008] Various advances in the catheter art now make it possible to
individual electrodes include a multitude of (e.g., sixty-four
individual electrodes) in a single diagnostic or mapping electrode.
It is reasonable to believe that further advances will enable still
more electrodes to be used. However, as more and more electrodes
are added, it becomes more and more difficult for the attending
medical personnel to visualize and interpret the additional data
that are made available by such devices. Maximum device
effectiveness is realized when the attending medical personnel are
able quickly and accurately to visualize the catheter within the
body and interpret the information the device is providing. Along
with the greater resolution made possible by multiple electrode
catheters comes the need for simplified systems and methods of data
interpretation.
[0009] In one prior data interpretation approach, the various
waveforms acquired by the individual electrodes are displayed on a
screen. The medical personnel need to mentally integrate the heart
activity and position data as displayed on the recorder and
fluoroscopy screens in order to assess the health of the underlying
tissue. This approach considerable degree of skill and experience
on the part of the attending medical personnel. Furthermore,
information regarding the relative location of an ablation catheter
with respect to the multiple electrodes is not readily available.
More significantly, the system becomes impractical and unwieldy as
the number of electrode increases.
[0010] In another prior approach, information acquired from a
number of sequential locations of a roving electrode is digitally
sampled and combined to construct a model "surface" that is
displayed on a screen and that visually represents the tissue under
consideration. Although much easier to interpret than the prior
approach that required mental integration of various inputs, this
system, too, provides an unrealistic representation that requires
skill and experience to use effectively. Furthermore, the surface
is difficult to generate, as it requires that a roving electrode be
moved over the surface of the heart to reconstruct its geometry
point by point. To get reasonable accuracy, a high, sometimes
impractical, number of points is necessary.
[0011] As the number of electrodes, and, hence, the volume of raw
data, increase, it becomes more and more important to display data
in a form that can be readily interpreted and understood by the
attending medical personnel. Furthermore, it might be desirable to
display information in such a way that it can be easily related by
the physician to information provided by existing visualization or
imaging systems, such as a fluoroscopic system. Visually based
systems, which enable such personnel to "see" what is happening,
offer a viable means of presenting large amounts of data in a form
that can be readily grasped and understood. Graphical user
interfaces are one means by which such a goal can be achieved.
SUMMARY OF THE INVENTION
[0012] The invention provides a graphical user interface for
generating a visual display depicting the relative position and
orientation of a multiple electrode catheter within a body. The
graphical user interface includes a display screen, an image
generator for generating on the display screen an image of the
multiple electrode catheter, and a user-actuable control coupled to
the image generator for changing the relative position and
orientation of the image as displayed on the display screen.
[0013] It is an object of the invention to provide a new and
improved apparatus for facilitating the interpretation of data
acquired through the use of multiple electrode catheters.
[0014] It is a further object of the invention to provide a graphic
user interface that facilitates such interpretation.
[0015] It is a further object of the invention to provide a
graphical user interface that enables medical personnel to
visualize a multiple electrode catheter in place within a body.
[0016] It is a further object of the invention to provide a
graphical user interface that can display the location of roving
electrodes with respect to the multiple electrode catheter.
[0017] It is a further object of the invention to provide a
graphical user interface that can be readily implemented on
existing computer apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The features of the present invention which are believed to
be novel are set forth with particularity in the appended claims.
The invention, together with the further objects and advantages
thereof, may best be understood by reference to the following
description taken in conjunction with the accompanying drawings,
wherein like reference numerals identify like elements, and
wherein:
[0019] FIG. 1 is a simplified block diagram of a cardiac diagnostic
and treatment system having a multiple electrode catheter and a GUI
embodying various features of the invention.
[0020] FIG. 2 is a further simplified block diagram of the system
shown in FIG. 1 further including a fluoroscope for monitoring the
position of the multiple electrode catheter within a patient's
body.
[0021] FIG. 3 is a diagrammatic representation of a multiple
electrode catheter and a system of coordinates useful in describing
positions relative to the multiple electrode catheter.
[0022] FIG. 4(a) is a flowchart diagram useful in understanding an
algorithm used to rotate a wireframe display of a multiple
electrode structure using a mouse.
[0023] FIG. 4(b) is a flowchart diagram useful in understanding the
operation of an algorithm used to identify user-requested
electrodes within the wireframe display of the multiple electrode
structure.
[0024] FIG. 4(c) is a flowchart diagram useful in understanding the
operation of an algorithm used to associate markers or anatomical
features with the wire-frame display of the multiple electrode
structure.
[0025] FIG. 5 is a sample of a display screen generated by the GUI,
useful in understanding the look and feel thereof.
[0026] FIG. 6 is a sample of a display screen generated by the GUI
showing a multiple electrode structure within the right atrium of a
heart for purposes of diagnosing and treating atrial tachycardia
within the right atrium.
[0027] FIG. 7 is a sample of a display screen generated by the GUI
showing a multiple electrode structure within the left ventricle of
a heart for purposes of diagnosing and treating ventricular
tachycardia within the left ventricle.
[0028] FIG. 8 is a sample of a display screen generated by the GUI
showing a multiple electrode structure within the right atrium of a
heart for purposes of diagnosing and treating atrial flutter within
the right atrium.
[0029] FIG. 9 is a sample of a display screen generated by the GUI
showing the location of an ablation electrode during a tachycardia
ablation procedure.
[0030] FIG. 10 is a simplified diagram of a cardiac diagnostic and
treatment system having a switch driver connectable to a multiple
electrode catheter and display interface.
[0031] FIG. 11 is a representation of a switch matrix capable of
creating electrical paths between multiple electrode inputs and
multiple display channel outputs.
[0032] FIG. 12 is schematic diagram of a switch element within the
switch matrix of FIG. 11.
[0033] FIG. 13 is a simplified representation of a switch matrix
forming an electrical path configuration through a patient.
[0034] FIG. 14 is a general circuit equivalent for an active path
configuration of the switch matrix of FIG. 13.
[0035] FIG. 15 depicts the impedance/voltage relationship through
the effective resistance of the active path configuration shown in
FIG. 14.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0036] Referring to FIGS. 1 and 2, a system 10 for diagnosing,
treating or otherwise administering health care to a patient 12
using a multielectrode catheter 14 is shown. In the illustrated
embodiment the system 10 comprises a cardiac diagnostic system that
can be used to diagnose and treat abnormal cardiac conditions, such
as arrhythmias. It will be appreciated, however, that the system 10
is illustrative and that the invention can be practiced in settings
other than cardiac care.
[0037] As illustrated, the system 10 includes a multielectrode
catheter 14 deployable within the heart of the patient 12. The
catheter 14, which can comprise a catheter of the type shown in
co-pending application Ser. No. 08/587,251, filed Jan. 16, 1996,
entitled Multiple Electrode Support Structure and commonly owned by
the assignee hereof, includes up to sixty-four individual
electrodes 16 disposed on a plurality of splines 18. Each of the
electrodes 16 is connected to an individual conductor in a multiple
conductor cable 20. The cable 20 terminates in one or more
connectors through which electrical connection can be made to the
individual conductors and, hence, to the individual electrodes.
[0038] The system 10 also includes a fluoroscope 22 (FIG. 2) of
known construction that can be used to monitor the position of the
catheter 14 in the body. The fluoroscope 22 includes a head 24 that
generates and directs X rays into the body, a sensor and an image
intensifier 26 that detects the X-rays passing through the body,
and a screen 28 that displays the resulting images. The fluoroscope
22 can be rotated around the patient's body to obtain views from
different viewing points or "fluoroangles". Certain fluoroangles
are more frequently used in the field of fluoroscopy. FIG. 3
illustrates the viewing angles for such views, with respect to the
coordinate system associated to the wireframe representation of the
multiple electrode structure. These views are:
Right-Anterior-Oblique (RAO) 30 or 45, Anterior-Posterior (AP) and
Left-Anterior-Oblique (LAO) 30 or 45. The AP View is provided when
image intensifier 26 is positioned perpendicular to the patient's
chest. The LAO view is provided when the image intensifier 26 is
positioned over the left side of the patient's chest. The RAO view
is provided when the image intensifier 26 is positioned over the
right side of the patient's chest. The angle with respect to the AP
orientation is attached as a suffix to the LAO or RAO nomenclature
(e.g. if the angle is 30 degrees the view is labeled RAO30 or
LAO30). The GUI can also provide virtual views from angles
physically unrealized. For example, the Inferior view displays the
multiple electrode structure as seen by a viewer looking
horizontally from the patient's feet. The Superior view displays
the multiple electrode structure as seen by a viewer looking
horizontally from the patient's head. The Left or Right 90 views
are views orthogonal to the main views AP, RAO or LAO depending on
which view has been selected for display in the left half-screen.
For example, if the left half-screen displays a LAO 30 view, Right
90 would be the corresponding orthogonal view and equivalent to RAO
60. Similarly, Left 90 would correspond to LAO 120, although this
angle is not physically realizable. Some fluoroscopes include a
pair of heads and sensors oriented at right angles to each other.
The simultaneous orthogonal views presented by such fluoroscopes
further assist the physician in following the progress of the
catheter into the patient's body.
[0039] The system 10 further includes a biological recorder 30 of
known construction that broadly functions to record, store, analyze
and display signals acquired by the electrodes 16 of the catheter
14. The biological recorder 30 includes a recording/processing unit
that records and processes acquired signals and further includes a
display unit that displays the acquired signals to the attending
health care personnel.
[0040] The system 10 further includes an interface 32 that enables
information acquired by the multiple electrodes to be loaded into
the biological recorder. To this end, the interface 32 functions
broadly to couple individual electrodes or groups of electrodes to
the biological recorder. By so coupling the electrodes, it is
possible to route all the acquired data into the biological
recorder even though the number of available inputs into the
recorder may be less than the total number of electrodes.
[0041] The interface 32 also applies a known electrical field
through the roving electrode 19 and measures the potential
distribution generated at the electrodes 16. This information is
then used to estimate the location of the roving electrode. A
system and method for determining the location of electrode within
body has been disclosed in co-pending application Ser. No.
08/745,795 filed Nov. 8, 1996 entitled "Systems and Methods for
Locating Guiding Operative Elements Within Interior Body Regions"
and application Ser. No. 08/679,156 filed Jul. 12, 1996 entitled
"Systems and Methods for Guiding Movable Electrode Elements within
Multiple Electrode Structures" and commonly owned by the assignee
hereof Other methods of localizing electrodes could be employed by
the skilled in the art such as presented in prior art U.S. Pat. No.
5,558,091.
[0042] The interface 32 is also coupled to an external,
user-actuatable, microprocessor-based computer control such as a
laptop computer 34 having a keyboard 36 and display screen 38.
Preferably, a mouse 39 is included with the computer 34. The
interface 32 operates under the command of the computer 34 to
interconnect individual electrodes 16 with individual inputs to the
biological recorder 30. The Interface 32 also communicates back to
the computer 34 information about the location of the roving
electrode 19. The computer 34, in turn, responds to requests and
instructions entered onto a keyboard 36 by the health care
personnel and commands the interface unit 32 to switch among the
electrodes 16 as required to achieve the desired function. Commands
to configure/test the unified switching system are issued by the
computer 34 through the keyboard 36.
[0043] A diagnostic and treatment system appropriate for use with
the present invention is shown and described, for example, in U.S.
Application Ser. No. 08/770,971 entitled, "Unified Switching System
for Electrophysiological Stimulation and Signal Recording and
Analysis," filed Dec. 12, 1996 and commonly owned by the assignee
hereof, the specification of which is incorporated by reference
herein.
[0044] The computer 34 receives roving electrode location
information from the interface 32 preferably via a serial bus such
as RS 232. The location information can comprise three numbers
indicating the 3-D coordinates of the roving electrode.
Alternatively, it can be a data stream of 64 bits with one bit
corresponding to each of the 64 electrodes 16 of the multiple
electrode structure 14. A bit equal to logic 1 indicates that the
particular electrode 16 resides at less than a predefined distance
threshold (e.g. 2mm) away from the roving electrode 19. A bit equal
to logic 0 indicates that the particular electrode 16 resides at
more than the predefined distance threshold away from the roving
electrode 19. As such, the approximate location of the roving
electrode 19 can be retrieved by knowing in the proximity of which
of the electrodes 16 the roving electrode resides.
[0045] The invention comprises a Graphical User Interface (GUI)
that is implemented on, and resident in, the computer 34. The GUI
functions to provide the attending medical personnel with a
pictorial or graphic representation of the multielectrode catheter
14 within the patient's body. The various individual electrodes 16
and roving electrode 19 are indicated, as are their locations and
orientations relative to themselves. The representation of the
multielectrode catheter 14 and/or roving electrode 19 may be
manipulated on the display screen 38 until it suggests the
orientation of the catheter 14 within the patient's body 12. The
orientation may be guided and confirmed by comparing the appearance
of the representation of the catheter 14 to the appearance of the
catheter on the fluoroscope display 28. Such display helps "orient"
the attending personnel with respect to the catheter 14 and the
patient's body 12 and thus helps them interpret the data provided
by the catheter 14.
[0046] The display of the position of the roving electrode 19 helps
the physician in guiding diagnosis or therapy application.
[0047] The invention makes use of the human ability to process
information more readily when presented in a graphic form than when
presented as a series of numerical data points. The graphic model
of the multielectrode catheter 14 within the body 12 that the GUI
provides enables the attending personnel to visualize the locations
of the individual electrodes 16 in relation to actual tissue and
thus helps the personnel interpret the data obtained by each
electrode 16. The GUI further enables the personnel to "turn" their
point of view relative to the catheter 14 and the patient 12 and
thus "see" the catheter 14 from positions that are not physically
realizable. The GUI also enables the personnel to label various
electrodes 16, enter notes onto the display 38 and otherwise add
visual or informational prompts or cues that further aid in
interpreting the information provided by the catheter 14.
[0048] The GUI provides a graphical model that represents how a
catheter 14 would be situated relative to various anatomical
structures if certain assumptions concerning the catheters'location
are correct. By reference to this model, the attending personnel
are able to visualize were each electrode 16 and spline 18 is
located within the patient's body 12.
[0049] During a diagnostic or other medical procedure, the
fluoroscope 22 is used to monitor the position of the catheter 14.
The GUI provides a simplified and idealized representation that
supplements the fluoroscopic image 28.
[0050] When placed into operation, the GUI displays a simplified,
idealized graphical image of the particular type of multielectrode
catheter 14 being used in the procedure. In the illustrated and
preferred embodiment, the GUI provides a split screen image having
a left panel 40 and a right panel 42. A wire-frame image 44 of the
catheter 14 appears in standard orientations on both the right and
left panels. The particular GUI shown and described is intended for
use with a single type of multielectrode catheter 14 of the type
shown and described in U.S. Pat. No. 5,549,108 issued Aug. 27, 1996
entitled "Cardiac Mapping and Ablation Systems" and U.S. Pat. No.
5,509,419 issued Apr. 23, 1996 entitled "Cardiac Mapping and
Ablation Systems" and commonly owned by the assignee hereof.
Accordingly, information regarding the catheter is already retained
within the GUI. Alternatively, in other embodiments, the system
operators can enter the type of catheter that is being used. The
GUI can then display the type of catheter thus selected.
[0051] After the initial form of the catheter 14 is displayed, it
is necessary next, to set the view in the left panel 40 to match
the view of the fluoroscope 28. To this end, the attending
personnel compares the fluoroscopic image 28 of the catheter 14 and
then manipulates the GUI image 44 on the left panel 40 so that the
catheter 44 shown thereon closely matches the live view as seen on
the fluoroscopic display 28. To accomplish this, the GUI includes a
plurality of on-screen buttons 46 (FIG. 3) that can be pressed to
cause the catheter image 44 to rotate. These buttons are the X, Y
and Z orientation buttons. These buttons are used to change the
relative position of the multiple electrode catheter orientation
from its initial position. Thus, the system operator moves the
cursor to one of the orientation buttons and presses the left mouse
button. This action causes the catheter image 44 to rotate about an
idealized coordinate axis 48 located at the virtual multiple
electrode catheter center shown in FIG. 3. As to be expected, the X
orientation button rotates the multiple electrode catheter image 44
in either a left-to-right or right-to-left direction, the Y
orientation button rotates the multiple electrode catheter image in
either a top-to-bottom or bottom-to-top direction and the Z
orientation button rotates the multiple electrode catheter image in
either a clockwise or counterclockwise direction.
[0052] Assume a point P.sub.0 of coordinates Y, y.sub.0, z.sub.0.
on the envelope surface of the structure 14. After a rotation of
angle .alpha.. about the X axis the new position of P(x, y, z) is
given 1 [ x y z ] = [ 1 0 0 0 cos ( ) sin ( ) 0 - sin ( ) cos ( ) ]
[ x 0 y 0 z 0 ]
[0053] by equation(1).
[0054] Equation (2) and (3) define rotations of angle a about the Y
and Z axis, respectively: 2 [ x y z ] = [ cos ( ) 0 sin ( ) 0 1 0 -
sin ( ) 0 cos ( ) ] [ x 0 y 0 z 0 ] [ x y z ] = [ cos ( ) sin ( ) 0
- sin ( ) cos ( ) 0 0 0 1 ] [ x 0 y 0 z 0 ]
[0055] In general, if a sequence of X, Y, or Z rotations is
performed, the final coordinates of the point P depend on the exact
order the rotations are performed in.
[0056] Alternatively, the system operator may utilize the mouse
controls to rotate the multiple electrode catheter image. Whenever
the cursor is positioned in the left panel 40 and the left mouse
button is pressed, the cursor changes from an arrow-style image to
that of a hand-style image 50. This action causes the movement,
that is to say, the rotation of the multiple electrode catheter
image in response to the movement of the mouse by the system
operator. By keeping the mouse left button pressed, the system
operator may position the multiple electrode catheter image. When
the left mouse button is released, the multiple electrode catheter
image 44 remains in the current orientation. FIG. 4(a) presents the
flowchart of the algorithm for the mouse-driven rotation. Element
70 draws the hand icon when the mouse button is pressed. Element 72
computes the direction of mouse movement. Based on this
information, element 74 computes two rotation angles about the X
and Y-axes. Element 76 performs the actual rotation based on
equations (1) and (2) above. The action of rotating the wire-frame
multiple electrode catheter representation 44 in the left panel 40
by means of X, Y and Z orientation button or mouse movement may be
repeated until the system operator is satisfied with the
orientation of the multiple electrode catheter image in reference
to the fluoroscopic image 28.
[0057] Preferably, the wire-frame representation 44 of the multiple
electrode catheter 14 shows a plurality of splines 52 corresponding
in number to the actual number of splines 18 used in the
multielectrode catheter 14 and further shows a plurality of
electrodes 54 on each spline 52 corresponding in number to the
actual number of electrodes 16 on each spline 18. In the preferred
embodiment, splines 52 and electrodes 54 on the wire-frame image 44
are highlighted, colored differently, sized distinctly or otherwise
distinguished visually from the others to provide a representation
of the multiple electrode catheter in a virtual three-dimensional
space where the center of the wire-frame model 44 is designated as
the center of that three-dimensional space. In the illustrated
embodiment, the wire-frame image 44 is generated such that splines
52 and electrodes 54 which lie in the background of the
three-dimensional space (i.e., behind the center of the
three-dimensional space as viewed from the system operator's
viewing angle) appear darker or shadowed compared to the splines 52
and electrodes 54 appearing in the foreground. This enhances the
three-dimensional appearance of the multiple electrode catheter
image 44 on the screen 38.
[0058] Once the orientation of the virtual multiple electrode
catheter image is matched to the real fluoroscopic image, as viewed
by the system operator, it may be saved or stored in the computer
memory by pressing the "Save View" button. The "Save View" button
provides for the system operator to save or store the current
multiple electrode catheter image as any of the standard views,
i.e., the "AP" "LA045", "LA030", "RA030" or "RA045" views.
[0059] To further assist the operating personnel in interpreting
what they see, it is frequently helpful to provide other viewing
angles that are related to the standard fluoroscopic view but not
realizable by such equipment. To this end, the GUI based on the
properly orientated image shown in the left panel of the display,
is operable to generate and display multiple electrode catheter
images in the right panel that are orthogonal to the view in the
left panel. Such orthogonal views are displayed in the right panel
relative to the view set in the left panel.
[0060] In the illustrated embodiment, the GUI provides orthogonal
views calculated from the "Superior", "Inferior", "Left 90" and
"Right 90" views.
[0061] Preferably, the wire-frame representation 44 of the multiple
electrode catheter 14 shows a plurality of splines 52 corresponding
in number to the actual number of splines 18 used in the
multielectrode catheter 14 and further shows a plurality of
electrodes 54 on each spline 52 corresponding in number to the
actual number of electrodes 16 on each spline 18. Preferably, one
or more of the splines 52 or electrodes 54 is highlighted or
otherwise distinguished visually from the others to provide a
reference for orienting the displayed wire-frame image 44. In the
actual catheter 14, one or more of the splines 18 or electrodes 16
are provided with a fluoroscopic marker that appears on the
fluoroscope screen 28 and that serves to identify a particular one
of the electrodes 16 for reference purposes. The electrode 60
highlighted by the GUI corresponds to this electrode and is
positioned to closely match the position of the corresponding
electrode on the fluoroscope screen 28.
[0062] The described procedure thus coordinates the "three
dimensional" wire-frame multiple electrode catheter representation
44 generated and displayed by the GUI with the two-dimensional
display of the actual multiple electrode catheter 14 shown on the
fluoroscope screen 28.
[0063] After the displayed multiple electrode catheter image 44 is
properly oriented, the view can be saved by clicking the "Save
View" and "OK" buttons that appear on the display screen 38.
[0064] In the illustrated embodiment, the wire-frame image 44
generated on the left panel 40 of the display 38 corresponds to the
view of the multiple electrode catheter 14 displayed on the
fluoroscope screen 28. To further assist the operating personnel in
interpreting what they see, it is frequently helpful to provide
other views that are not easily realizable using the fluoroscopic
equipment 22. To this end, the GUI, based on the properly oriented
image 44 shown on the left panel 40 of the display 38, is operable
to generate and display images 44' of how the multiple electrode
catheter image 44 would appear if view from other angles. Such
alternate views are displayed on the right panel 42 of the display
38.
[0065] In the illustrated embodiment, the GUI provides "Superior,"
"Inferior," "Left 90.degree." and "Right 90.degree." views. These
views are obtained by clicking the appropriately labeled
corresponding buttons on the screen 38. The image appearing on the
right panel 42 of the display 38 tracks the orientation of the
image 44 on the left panel 40. Thus, if the image orientation on
the left display panel 40 is changed or adjusted, the right image
441 will also change to reflect the new orientation of the catheter
14 relative to the body.
[0066] In the illustrated embodiment, fluoroangles between
-90.degree. and +90.degree. can be used and can be entered into the
GUI. Thus the GUI can be still be effectively used if, for some
reason, the attending personnel elect to position the fluoroscope
to a non-standard fluoroangle. In the illustrated embodiment, views
at the standard fluoroangles of -45.degree., -30.degree.,
0.degree., +30.degree. and +45.degree. can be automatically saved.
Customized views at nonstandard fluoroangles can also be named and
saved.
[0067] As previously mentioned, the primary function of the GUI is
to provide a visual image or model 44 that assists the operating
personnel in visualizing the multiple electrode catheter 14 within
the patient's body 12 and interpreting the data acquired from the
multiple electrode catheter 14. Although this is largely achieved
by orienting the wire-frame display representation of the electrode
basket to match the actual image provided by the fluoroscope, the
GUI provides several additional functions that further enhance its
effectiveness. Various additional functions are described
below.
[0068] A MARKERS function is provided which enables the operator to
alter and enhance the displayed multiple electrode catheter wire
frame image. The MARKERS function includes an ADD MARKER function
that enables the operator to add an identifier or marker to
selected locations of the electrode image 44 displayed in the left
screen 40. This function is useful if the operator wishes to mark
selected locations that are significant or of interest, such as
mapping sites, ablation sites, etc. By having such sites
highlighted or otherwise distinguished, the operator is better able
to remain coordinated and oriented with the displayed image and,
therefore, better able to interpret data recovered by the multiple
electrode structure. The markers appear on the surface defined by
the various splines 52.
[0069] The MARKERS function is used by clicking the ADD MARKER
button that appears on the screen after the general "MARKERS"
button is clicked. Pressing the right mouse button on an electrode
causes a marker to appear on the screen. With the right button thus
depressed, the mouse is used to "drag" the marker over the implied
surface of the multiple electrode catheter to the desired location.
When the right button is released, the marker is "dropped" into the
desired marker location. Markers can thus be placed near electrodes
on either the foreground or background of the multiple electrode
catheter.
[0070] FIG. 4(b) shows the flowchart of the algorithm used to add
markers. Element 80 assigns the initial x.sub.0, y.sub.0, z.sub.0
coordinates of the marker when the mouse button is pressed. These
initial coordinates are identical to those of the electrode 16
acting as origin of the placement. Element 82 generates the marker
symbol and inserts the corresponding software data structure into a
linked list. Element 84 computes the direction of the mouse
movement based on information received from the mouse port. Element
86 converts the direction information into two rotation angles,
about the X and Y-axes, respectively. Element 88 computes the new
location of the marker based on equations (1) and (2). Element 89
assigns the final x, y, z-coordinates to the marker when the mouse
button is released. Markers are created as data structures
comprising: pointer to previous marker, order number, coordinates,
comments, time stamp and pointer to next marker.
[0071] Also included in the MARKERS function is a COMMENT function
that enables the operator to add custom notes or comments to each
marker. For example, if the operator wishes to comment on the
significance of each selected, marked site, the COMMENT function
can be used for this purpose. A COMMENT window appears as soon as
the marker is "dropped" at the selected site. A time stamp is
preferably included in the comment. The operator can enter the
desired comment into the comment window using the computer
keyboard. By clicking the OK button, the comment thus entered is
saved. If no comment is desired, the CANCEL button can be clicked.
A PREV. COMMENT button is provided which, when actuated, displays
comments previously entered with earlier markers. A NEXT COMMENT
button displays comments associated with later entered markers.
Once a marker is "dropped," its comments can be retrieved by
placing the cursor onto the marker and pressing the right mouse
button.
[0072] A DELETE MARKER function is provided for deleting previously
entered markers. This function is actuated by clicking on the
DELETE MARKER button and thereafter placing the cursor on the
desired marker. When the right mouse button is pressed, the
selected marker is deleted. When a DELETE operation is performed
the corresponding marker data structure is removed from the linked
list by employing well-known data structure software techniques.
The MARKERS function is terminated by clicking the CLOSE
button.
[0073] The GUI also provides a mapping function that enables the
operator to create any of five types of binary maps. The available
mapping functions are (1) EARLY ACTIVATION, (2) FRACTIONATION, (3)
GOOD PACE MAP, (4) CONCEALED ENTRAINMENT and (5) USER DEFINED and
are characterized as follows:
EARLY ACTIVATION
[0074] The EARLY ACTIVATION mapping function identifies and marks
the electrodes where early depolarization of the heart tissue has
occurred. Early depolarization is often an indicator of abnormal
heart tissue adjacent the electrode.
FRACTIONATION
[0075] The FRACTIONATION mapping function identifies and marks the
electrodes where the electrograms sensed by such electrodes appear
fractionated or broken in appearance. Again, the existence of
fractionated electrograms a particular electrode site is often an
indicator of abnormal cardiac tissue at that site.
GOOD PACE MAP
[0076] The GOOD PACE MAP mapping function identifies and marks the
electrodes with high pace mapping matching index. This index
reflects how many of the morphologies of 12-lead surface
electrocardiograms (ECG) acquired during non-induced arrhythmia
match the morphologies of the same signals acquired during paced
induced arrhythmia from the particular electrode. If by pacing from
a particular electrode 16, a high number of the 12-lead ECG
morphologies are similar during non-induced and pace-induced
arrhythmia then it is likely that the particular electrode 16
resides close to an arrhythmogenic focus.
CONCEALED ENTRAINMENT
[0077] The CONCEALED ENTRAINMENT mapping function identifies and
marks the electrodes where arrhythmia entrainment was achieved.
Abnormal cardiac tissue often is located electrodes exhibiting
CONCEALED ENTRAINMENT.
USER DEFINED
[0078] The USER DEFINED mapping function enables the user to
specify particular criteria to be used for categorizing signals
obtained by the multiple electrodes. Electrodes providing signals
meeting the selected criteria are identified and marked. The USER
DEFINED mapping function allows the physician to locate areas of
cardiac tissue exhibiting certain preselected characteristics and
further enhances the diagnostic function of the system.
[0079] The various mapping functions are of importance in
identifying potential ablation sites. Frequently, abnormal cardiac
tissue, which can be effectively treated through ablation, often
exhibits more than one abnormal characteristic. Such sites
frequently appear on two or more of the EARLY ACTIVATION,
FRACTIONATION and CONCEALED ENTRAINMENT maps. If the same electrode
or groups of electrodes appear on two or more of the ACTIVATION,
FRACTIONATION, GOOD PACE MAP and CONCEALED ENTRAINMENT maps, a
likely site for ablation is particularly well indicated.
[0080] Numeric values, such as activation time numbers, cardiac
signal voltages, or propagation velocities, can be associated to
each electrode of the multielectrode catheter structure. Then,
iso-30 values (i.e., isochronal, isopotential, isoconduction etc.)
can be generated. The iso-value maps can be used in association
with the binary maps, markers and anatomic features to further
identify potential ablation sites.
[0081] The mapping function is initiated by clicking the CREATE MAP
button that appears on the display screen. When this button is
clicked, a popup window appears offering a choice of any of the
five mapping functions. By clicking on the selected choice, the
desired mapping function is initiated.
[0082] After the desired mapping function is selected, the mouse is
used to drop binary map markers at the electrodes of interest. This
is done by moving the mouse to place the cursor over the electrode
of interest and then depressing the right mouse button to drop the
marker at the selected electrode. The algorithm for generating
binary map markers is substantially similar to that shown in FIG.
4(b). The only difference is that the rotation step 208 is not
performed. T he binary map markers are directly attached to the
selected electrode 16. Similar data structure techniques are used
to create and update the required binary map linked lists. The data
structure corresponding to a binary map marker comprises: pointer
to previous marker, electrode number, binary map type, comment,
time stamp, iso-value type and pointer to next marker. After the
selected electrodes are thus marked, a different type of binary map
can be selected or the CLOSE button appearing on the pop-up window
can be clicked. Specific comments can be entered by the operator
using the computer keyboard. If the comments are acceptable, the OK
button is then clicked. If not, the CANCEL button is clicked and
the comments are not saved. Comments can later be retrieved by
placing the cursor over a binary map marker and then pressing the
right mouse button.
[0083] Various other functions are provided in connection with the
mapping function. A SHOW MAP function can be selected by clicking
the SHOW MAP button. This function displays the types of binary
maps that are available. By clicking on one of the listed types,
the selected binary map will then be displayed. The types of maps
being displayed will be indicated with a check mark (.check
mark.).
[0084] A CLEAR MAPS button functions, when clicked, to delete and
clear all existing binary maps.
[0085] A REMOVE MAP POINTS button operates, when clicked, to clear
a specific map point by placing the cursor on the map point to be
removed and clicking the right mouse button.
[0086] A CLOSE button functions, when clicked, to close the BINARY
MAP function. Still additional functions are provided by the
GUI.
[0087] A FEATURES function displays a pop-up window with choices
for anatomic markers. The anatomic markers function to indicate on
the display the location of certain anatomic structures or
landmarks (e.g., the aortic valve, the inferior vena cava, the
superior vena cava etc.) relative to the multiple electrode
catheter. Having the relative locations of such anatomical
structures displayed relative to the multiple electrode catheter
and its other features helps the physician in guiding the catheter,
and in mapping and treating the cardiac tissue.
[0088] To operate this function, the FEATURES button is clicked,
which causes a pop-up window to be displayed. The window displays a
number of choices for anatomic markers. The desired anatomic marker
is selected using the cursor, and the marker is then dragged to the
desired location using the right button of the mouse. At the
desired location, the right mouse button is released to drop the
marker at the desired location. The algorithm which inserts these
anatomic markers works similarly to that shown in FIG. 4(b).
However, the anatomic markers are not created as linked lists data
structures. The anatomic markers can be deleted as a group by
clicking on the CLEAR ALL FEATURES button, or can be selectively
deleted by clicking the REMOVE FEATURE button.
[0089] A PRINT function can be selected by clicking on the PRINT
button. This function prints both multiple electrode catheter views
plus current and existing comments on the system's default
printer.
[0090] SAVE VIEW function saves the selected principal view (i.e.,
the left screen panel) when actuated. All other views are updated
accordingly.
[0091] SHOW SPLINES function labels the individual splines of the
electrode basket when actuated. This button also turns into HIDE
SPLINES to facilitate label removal when desired. Spline labels in
the foreground appear brighter than spline labels in the background
to further enhance the three-dimensional effect provided by the
GUI.
[0092] A FIND SITE function operates, when actuated, to enable the
operator quickly to locate a particular electrode. When this
function is actuated, the operator enters the designated electrode
onto the keyboard and the GUI then highlights the electrode thus
selected. In the illustrated embodiment, a circle is flashed around
the selected electrode until a next action is taken. FIG. 4(c)
illustrates the flowchart of the algorithm that implements the Find
Site function. Element 92 accepts a user-entered electrode number
(e.g. A4, D3) and returns an entry to a 8.times.8 matrix associated
to the electrodes 16 on structure 14. Element 94 accepts as input
the matrix entry and returns the x, y, z coordinates of the
user-selected electrode 16. Element 96 draws and flashes a circle
around the x, y, z coordinates received from element 94. Element 96
also checks whether any other action is issued by the computer 34.
If the answer is yes then it stops the Find Site function and
returns to normal screen.
[0093] A ZOOM VIEW L function operates, when actuated, to expand
the left half-screen to a full screen view.
[0094] A ZOOM VIEW R function operates, when actuated, to expand
the right half-screen to a full screen view.
[0095] A RESET function operates to reset the screen to a default
view when actuated. Various examples of the GUI in use are shown in
FIGS. 6, 7, 8 and 9.
[0096] FIG. 6 represents the multiple electrode structure within
the right atrium of the heart. Display panel 40 shows the wire
frame image 44 from the AP view, while the right panel 42 shows the
image 441 from the inferior view. The relative locations of the
Superior Vena Cava and Inferior Vena Cava are marked "SVC" and
"IVC" respectively on the displays. A first early activation site
is indicated by the marker .diamond-solid.1, while a second early
activation site is indicated by the marker .diamond-solid.2. The
user-entered legend under the display indicates that the first site
was ablated at time 09:42:36, while the second site was ablated at
time 09:43:02. The legend further indicates that the detected
arrhythmia was rendered noninducible following such ablation,
thereby indicating a successful treatment.
[0097] FIG. 7 represents the multiple electrode structure within
the left ventricle for treatment of left ventricular tachycardia.
In FIG. 7, the view in the left display panel 40 is from the AP
position, while the view in the right panel 42 is from the RAO 45
position. In this example, the various binary mapping functions
have been used, and two sites satisfying two or more of the
selection criteria have been located and indicated by the symbols
.diamond-solid., .circle-solid., and *. In particular, two sites
exhibiting fractionation and concealed entrainment have been
located and identified. Such sites are likely candidates for tissue
ablation.
[0098] FIG. 8 represents the multiple electrode structure within
the right atrium for treatment of atrial flutter. The view in the
left panel 40 is from the AP position, while the view in the right
panel is from the LFT 90 position. Three markers, .diamond-solid.1,
.diamond-solid.2, and .diamond-solid.3 are shown in both views.
According to the user-entered legend, these markers indicate first,
second and third atrial flutter ablation points, respectively.
[0099] FIG. 9 depicts the GUI being used to guide the roving
electrode 19. The view in the left panel 40 is from the AP
position, while the view in the right panel 42 is from the SUPERIOR
position. The relative position of the roving electrode is
indicated by the elongate symbol. The highlighted symbols *
adjacent the electrodes C6 and C7 indicate early activation sites.
The user-entered legend indicates a potential tachycardia ablation
site between these electrodes.
[0100] The GUI is preferably configured to operate on WINDOWS
compatible laptop or desktop computers. Preferably, the computer
should include a 486DX or higher processor operating at a clock
frequency of 66 MHz or higher. A hard disk capacity of 360 MB, and
a main memory capacity of 4 MB should be available. Preferably, the
GUI is configured to run on WINDOWSS 3.1, WINDOWS 950 or NT
operating systems. The GUI is preferably realized as a "C" language
program created using known programming techniques.
[0101] Referring to FIG. 10, in an alternate preferred embodiment,
a switch matrix 101 is provided as part of a patient interface
system 102 for use in conjunction with multiple electrode
catheters, such as basket catheter 111. In particular, the basket
catheter 111 includes an elongate catheter body 106 having a
plurality of flexible spline elements 103 connected at one end.
Each of the spline elements 103 carries a plurality of electrodes
105 adapted for making electrical contact with the internal tissue
regions of a patient's heart.
[0102] The other end of the catheter body 106 is adapted for
connecting to a switch matrix 101. In particular, referring
additionally to FIG. 11, a respective electrical lead 110 extends
from each electrode 105 through the catheter body 106, with the
leads 110 connectable to the switch matrix 101 as respective inputs
122. In this manner, the respective leads 110 provide a separate
electrical path from the switch matrix inputs 122 to the respective
electrodes 105. The effective path resistance "seen" by each lead
110 through switch elements (not shown) of the switch matrix 101 is
represented by a corresponding resistance 107, which may vary for
each particular switch path 108 formed through the switch matrix
101. This resistance 107 is preferably minimized, typically between
10-1000 .OMEGA.in a preferred embodiment.
[0103] Each signal path 108 formed through the switch matrix 101 is
independent from the other paths, as represented by a high
resistance 109 between each path 108. Since the overall resistance
seen by an electrode lead 110 at an input 122 of the switch matrix
101 can be relatively large in known patient applications, the
switch matrix 101 must operate over a large fluctuating voltage
range due to the presence of a varying signal source 104. For
example, signal source 104 can be a cardiac stimulator used for
pacing or a source of currents used for diagnosis of a patient's
heart, or other body organs or functions.
[0104] The switch matrix 101 comprises a multiplicity of switch
elements, which are preferably implemented by MOSFETs as part of an
application specific integrated circuit (ASIC). The switch matrix
101 is capable of interconnecting multiple inputs 122 from the
catheter 111 to either multiple channel outputs 123 or source
receptacles 124. In particular, the switch matrix 101 allows for
any input 122 to be selectively connected to any channel 123 or
source receptacle 124 output. While FIG. 11 depicts ninety-six
inputs 122 selectively connectable to seventy-two channel outputs
123 and/or four cardiac stimulator receptacle outputs 124, it will
be appreciated by those skilled in the art that the switch matrix
101 could be modified to provide selective cross-connection of any
number of inputs to outputs, including supporting multiple medical
diagnosis or therapeutical applications.
[0105] In particular, as shown in FIG. 11, when activated into an
"ON" condition, a given switch path 108a within the switch matrix
101 behaves as a low value resistor. Switch paths 108b in an OFF
condition behave as a high-resistance capacitance, thereby forming
an open loop and precluding path formation.
[0106] For example, cardiac-pacing currents can vary .+-.20 mA, as
represented by the varying source 104 in FIG. 10. In this instance,
source 104 may include a pulsed current source or a low-, medium-
or high-frequency voltage or current sources. These currents may
include pacing currents, physiological signals, or recording
signals. Since the bipolar resistance seen between any two inputs
122 can be up to 1.5 k.OMEGA. in human patient applications, a
switch path 108 is thereby exposed to a possible voltage swing of
over .+-.30V. However, the reference voltage for a particular
switch path will vary with the relative voltage difference of the
body potential of a patient. Because this relative voltage can
fluctuate, an activated switch matrix path 108a will not always
have a fixed reference voltage. Thus, upon activation, transistor
substrates (not shown) within the switch matrix 101 must be able to
"float" so as to permit the formation of an active switch matrix
path 108a, even though the relative voltage may widely
fluctuate.
[0107] Accordingly, referring to FIG. 12, a preferred CMOS
switching circuit 125 is provided which floats with the average
body potential of a patient and is capable of withstanding a large
voltage variation.
[0108] In particular, an input voltage can be applied at 130
between terminals 178 and 179. The positive terminal 178 is
connected to the gate of a transistor 134 at node 155. The gate of
transistor 134 at node 155 is also connected to the gate of a PMOS
transistor 135. The drain of transistor 135 is connected to the
source of transistor 134, and the drain of a transistor 133 at node
156. The gate of transistor 133 is tied to a transistor 132 at node
154. The gate of transistor 132 at node 154 is tied to the drain of
transistor 132 at node 153. A current source 131 provides a current
to the source of transistor 132 at node 153. The source of
transistor 132 connects to a relative patient voltage V.sub.ss 152
at node 159, while the source of transistor 133 connects to
V.sub.ss 152 at node 160. V.sub.ss 152 is connected to the terminal
179. The current source 131 can be implemented using NMOS
transistors. The current can be defined by specifying the width and
length of the MOS channel. Typically, the current source 131
generates a few microamps.
[0109] The source of transistor 135 connects to the source of a
PMOS transistor 136 at node 157. The drain of transistor 136 at
node 157 is tied to the gate of transistor 136 at node 158. The
source of transistor 136 is tied to voltage source V.sub.dd 151 at
node 161 and to the source of a transistor PMOS 137 at node 162.
The gate of transistor 136 is tied to the gate of transistor 137 to
form a current mirror pair. The drain of transistor 137 is tied to
the drain of an NMOS transistor 138 at node 163. The gate of
transistor 138 is tied to the gate of an NMOS transistor 139 at
node 164. The drain of transistor 138 at node 163 is tied to the
gate of transistor 138 at node 164 so that transistors 138 and 139
form a basic current mirror pair. The source of transistor 138 is
tied to V.sub.ss 152 at node 165, and the source of transistor 139
is tied to V.sub.ss, 152 at node 166.
[0110] The drain of transistor 139 is tied to the drain of a PMOS
transistor 148 at node 167. The gate of transistor 148 is tied to
the gate of a PMOS transistor 147 at node 168. The gate of
transistor 147 is tied to the drain of transistor 147 at node 169
so that transistors 147 and 148 form a current mirror. The drain of
transistor 147 is tied to the drain of transistor 134 at node 169.
Both the source of transistor 148 and the source of transistor 147
are connected to an external source V.sub.cc 150 at nodes 172 and
171, respectively. The source of a PMOS transistor 149 is also
connected to V.sub.cc at node 173. The gate of transistor 149 is
tied to the drain of transistor 147 and the drain of transistor 134
at node 169. The drain of transistor 149 is tied to the drain of an
NMOS transistor 143.
[0111] The source of transistor 143 is tied to a positive terminal
of a current-controlled V.sub.source 140 at node 174. The positive
terminal of V.sub.source 140 at node 174 is tied to the drains of
transistors 148 and 139 at node 167. The negative terminal of
V.sub.source 140 is tied to the source of a PMOS transistor 144.
The drain of transistor 144 is tied to V.sub.ss 152 at node 170.
The gate of transistor 143 is tied to the gate of transistor 144 at
node 177. The source V.sub.source 140 is formed of NMOS transistors
and delivers a high/low voltage when the through current is at a
high/low value. Its high-voltage value can be defined be specifying
the width and length of the MOS channels.
[0112] The gates of two NMOS transistors 141 and 142 are tied
together at node 175 and connected to V.sub.source 140 and the
source of transistor 143 at node 174. The drain of a transistor 141
is tied to the source of a transistor 142 at node 176. The gates of
transistors 144 and 143, tied together at node 177, are connected
to the source of transistor 142 and the drain of transistor 141 at
node 176. The source of transistor 141 is connected to a terminal
145 while the drain of transistor 142 connects to a terminal 146.
Terminals 145 and 146 connect inputs 122 to outputs 123 or to
source receptacles 124, as shown in FIG. 11. The NMOS transistors
141 and 142 form one switch element of the switch matrix 101 in
FIG. 10. The ON resistance is defined by specifying the width and
length of the MOS channel. The equivalent resistance 178 seen
between 145 and 146 can change depending on the current passing
between terminals 145 and 146 and depending on the fluctuating
voltage build-up between the terminals 145 and 146.
[0113] To create the floating substrate characteristic, the switch
circuit 125 operates with two effective paths: an OFF path and an
ON path. The OFF path precludes electrical paths between particular
input electrodes and output channels. On the other hand, the ON
path configuration triggers the formation of an electrical path
108a between a desired input electrode 122 and a desired channel
output 123 or source receptacle 124. In the illustrated preferred
embodiment, V.sub.cc. is typically about +50 V, V.sub.dd is -25 V
and V.sub.ss is -30 V. It will be appreciated by one of skill in
the art that the values for V.sub.cc, V.sub.dd, and V.sub.ss may be
modified from these and yet still operatively perform.
[0114] The OFF path 108b occurs when the input voltage across
terminals 178 and 179 is very close to zero. The ON path 108a has
an input voltage that exceeds the threshold voltage and is
preferably 5 V
[0115] The resistance seen between terminals 145 and 146 in the OFF
configuration is typically greater than 1M.OMEGA.. The effective
resistance between terminals 145 and 146 in the ON configuration is
much less than the 1M.OMEGA. seen in the OFF configuration and is
preferably between 150 to 200.OMEGA., or lower. FIG. 15 shows a
typical dependence of the ON resistance versus the voltage at
terminals 145 or 146 with respect to V.sub.ss. As illustrated, the
ON resistance, R.sub.on, varies slightly with voltage within the
operating range.
[0116] For a better understanding of the switching circuit 125, we
will look first at OFF operation and then at ON operation.
[0117] Referring to FIG. 12, in the OFF configuration the voltage
across the input 130 between terminals 178 and 179 is approximately
0 V. In this configuration no switch matrix path is established.
For both the OFF and ON configurations, I.sub.0 from the current
source 131 preferably is 2 .mu.A. The current from current source
131 passes through a first basic current mirror consisting of two
matched NMOS transistors 132 and 133. Due to the characteristics of
a current mirror, the output current at the drain of transistor 133
remains close to 2 .mu.A. Since V.sub.in between terminals 178 and
179 is 0 V, the output current from this first current mirror
passes away from the NMOS transistor 134 through the drain of the
PMOS transistor 135.
[0118] The current at the source of the PMOS transistor 135 is
passed to a second current mirror pair consisting of matched PMOS
transistors 136 and 137. Again, due to the characteristic of a
current mirror, the current I.sub.o at the source of PMOS
transistor 136 is about equal to the current at the source of
transistor 137 toward the third current mirror comprising NMOS
transistors 138 and 139. Since transistor 139 conducts, it forces
the current to flow away from V.sub.source 140. Therefore, the
voltage seen across V.sub.source 140 is 0 V in an OFF
configuration. Current from V.sub.cc 150 will pass through
transistor 149, transistor 143 and through transistor 139 to
V.sub.ss, bypassing V.sub.source. Because V.sub.source.apprxeq.0 V,
the gate-to-source voltages of transistors 141 and 142 are close to
0 V. Therefore, transistors 141 and 142 do not conduct and the
switch element is OFF.
[0119] For the OFF configuration, a path between a particular input
122 and channel output 123 or source receptacle 124 will not be
activated and is therefore not connected in switch matrix 101
despite the presence of a floating reference voltage. In the ON
configuration, preferably 5 V are applied at the input 130 across
terminals 178 and 179. This voltage difference is selected to be
high enough to switch NMOS transistors on but not so high as to
make the switching circuit impracticable.
[0120] For the ON configuration, I.sub.0.apprxeq.2 .mu.A from
current source 131 passes through a first basic current mirror
consisting of the two matched NMOS transistors 132 and 133. Due to
the characteristics of the current mirror, the output current at
the drain of transistor 133 is similarly I.sub.0 .apprxeq.2 .mu.A.
The 2 .mu.A is then seen at the source of transistor 134. The
current at the drain of transistor 134 passes to the current mirror
comprising matched PMOS transistors 147 and 148. Because of the
characteristic of the current mirror to maintain current linearity,
the current level maintained at the drain of transistor 148 is
directed to V.sub.source 140. Thus, in the ON configuration current
from transistors 148 and 149 flows to the current-controlled
V.sub.source 140 since transistor 139 will be effectively off.
Transistor 143 will also be off because it will have a negative
gate-to-source voltage.
[0121] The V.sub.source 140 is selected to be sufficiently high to
overcome the threshold of the NMOS circuitry 141 and 142. The
voltage level at the output of V.sub.source 140 at node 174 must
also overcome the feedback gate-to-source voltage of PMOS
transistor 144. Since this gate-to-source voltage of transistor 144
is approximately 2 - 3 V, V.sub.source 140 in the preferred
embodiment is about 22 V, and the voltage appearing gate-to-source
at transistors 141 and 142 comes out to be about 19 to 20 V. It
will be appreciated by one skilled in the art that V.sub.source 140
can take on other values but primarily so long as sufficiently high
to properly bias the circuitry and overcome the feedback
voltage.
[0122] FIG. 13 diagrammatically represents operation of the switch
matrix 101 supporting an active electrical path 212 through a
patient 210, in conjunction with an exemplary pacing application.
In particular, the switch matrix 101 is connected to a current
source 206 at terminal 146, with the current source 206 is
connected to a patient ground 211. The current source 206
represents the current created by a pacemaker (not shown). The
switch matrix 101 has V.sub.cc, V.sub.dd, and V.sub.ss, connected
at outputs 203, 204 and 205, respectively. Terminals 145 and 146 of
the switch circuit 125 are represented by nodes 200 and 201 having
a resistance 202 between them. In particular, resistance 202
represents the resistance from transistors 141 and 142 when in the
ON configuration. Terminal 200 is shown connected to the heart of a
patient 210.. In a preferred embodiment, resistance 202 is
relatively low, e.g., approximately 200 .OMEGA.. The electrical
path 212 also includes a pacing electrode 209 disposed in the
patient 210. A reference electrode 207 electrically couples the
patient 210 to patient ground 211.
[0123] During operation, i.e., when the portion of the electrical
path 212 through the switch matrix 101 is "ON, the patient/pacing
impedance is that impedance seen by the path 212 from node 200 to
electrode 207, via the patient 210. This impedance primarily
includes the myocardial tissue impedance of the patient 210. In
known applications, this impedance can be up to 1.5 k.OMEGA.. Thus,
the voltage that develops at 200 or 201 with respect to patient
ground 211 is approximately equal to the current from the pacing
source 206 times the patient/pacing impedance (represented by
resistance 220 in FIG. 14). As indicated above, this current
typically varies .+-.20 mA. Thus, under "worst case" conditions,
the voltage that develops on terminals 145 and 146 of the switching
circuit 125 with respect to patient ground 211 can reach
approximately .+-.30 V. However, the voltage difference that simply
develops between terminals 145 and 146 is only .+-.20 mA times the
resistance 221. Under similar worst case conditions, this voltage
difference between terminals 145 and 146 can reach approximately
.+-.4 V.
[0124] Thus, in the ON configuration the NMOS substrate compensates
or floats so as to permit the formation of a switch matrix path
108a even though the relative patient voltage may fluctuate as much
as .+-.30V. Therefore, in an ON configuration, a switch matrix path
can be established despite substantial fluctuations in reference
voltage and current caused by a pacemaker or current source 104.
However, even in an OFF configuration, it is possible that
terminals 145 and 146 can still be exposed to voltage extremes of
about .+-.30V. This voltage extreme can occur in the switch matrix
101 where some paths are off while adjacent or neighboring paths
are on. Thus, where one terminal such as 146 is connected to a
patient, terminal 145 for one switch path 108a will be ON while a
terminal 145 for another switch path 108b may be OFF. In such a
situation, the voltage can build up between a terminal 145 and 146
for an unactivated path 108 b and reach about .+-.30 V. Therefore,
the circuit 125 may be exposed to a voltage range of .+-.30 V in
either an OFF or ON configuration.
[0125] While preferred embodiments of the invention have been shown
and described, it will be obvious to those skilled in the art that
changes and modifications can be made without departing from the
invention in its broader aspects, and, therefore, the aim in the
appended claims is to cover all such changes and modifications as
fall within the true spirit and scope of the invention.
* * * * *