This patent application generally relates to a programmable computer system that simulates electrical activity in excitable tissue. More particularly, it relates to a system that simulates electrical activity in a heart muscle.
The following three papers are incorporated herein by reference:
The spread of electric excitation through the intricate 3D structure of the heart muscle has been known to take widely varied forms, ranging from the orderly propagation seen during sinus rhythm to the marked disorganization seen during ventricular fibrillation. Observation of the diverse and sometimes complex patterns of conduction (for example, unidirectional block, reentry, spiral waves) as well as the responses to pacing maneuvers (for example, entrainment) suggests a nearly infinite array of possibilities.
Improved systems for simulating the electrical behavior of excitable tissues have been needed. Such systems may be used to deepen understanding of how electrical signals propagating through the heart muscle are related to arrhythmia and other heart conditions. Such systems may also lead to improvements in detection and correction of arrhythmias and other conditions. Such an improved system is provided by the following description.
One aspect of the present patent application is a method of simulating electrical propagation in a heart muscle on a computing device having a processor and a memory. The method includes providing a structural representation of a heart muscle. The structural representation includes a plurality of tissue elements. The plurality of tissue elements have a shape corresponding to shape of a heart muscle. The method includes storing a model of electric potential propagation through the structural representation in the memory. The model includes a piecewise linear equation describing electrical activity within each tissue element and a difference equation describing conduction from one of the tissue elements to an adjacent tissue element. The method also includes providing a first set of tunable parameters for inclusion in the piecewise linear equation and a second tunable parameter for inclusion in the difference equation. The method further includes tuning the first set of tunable parameters and the second tunable parameter in the model. The method also includes running said model on the processor of the computing device and displaying the simulated electrical propagation through the heart muscle over time.
Another aspect is a method of simulating electrical propagation in the heart muscle on a computing device having a processor and a memory. The method includes storing a model of electric potential propagation through a heart muscle in the memory. The method further includes running the model on the processor. The method further includes displaying simulated electrical propagation through the heart muscle produced by running said model on the processor, wherein said simulated electrical propagation is displayed in a time approximately equal to actual propagation time in a real heart muscle.
The foregoing will be apparent from the following detailed description, as illustrated in the accompanying drawings, in which:
a is a three dimensional representation of the human heart derived from human CT scan data in which the heart is divided into tissue elements;
b is a screen shot showing a modeling program offering a user choice for of selecting custom modeling parameters or selecting from a previously saved model;
c is a cutaway view of the 3D heart model showing electrical currents flowing through the excitable tissue structures and illustrating how the user can slice through the 3D heart model to view electrical activity spreading through the excitable tissue;
a is a screen shot of contiguous wavefronts identified at a particular time step of simulation;
b is a screen shot of a wave “family-tree” in which each node corresponds to a specific wave in a specific time step and lines are drawn between nodes with a strong spatial correlation;
One embodiment of the present patent application is a three dimensional model that provides for visualization of the flow of electrical potential and/or electrical current within the three dimensional structures of the heart muscle. This embodiment includes simulation of a user-definable two or three dimensional shape for the heart with its electrically excitable tissue and includes simulation of positioning electrodes, catheters, and stimulators in any arbitrary location in and around the electrically excitable tissue. This embodiment also includes simulation of the torso so that electrocardiograms obtained from surface mounted electrodes can be accurately modeled.
In one embodiment, data collected from imaging the torso, such as computerized axial tomographic (CT) scan images, is used to create a three dimensional model representative of a specific individual's anatomy, including the heart and surrounding tissue, as shown in
For 2D models, the electrically excitable elements of the model may include shapes such as triangles or squares. For 3D shell models of uniform thickness, the electrically excitable elements of the model may also include arbitrary 2D shapes, such as triangles or squares, as shown with triangular elements in
For 3D models of structures with variable and substantial thicknesses, each electrically excitable element is represented by a 3D shape, such as cubic or tetrahedral.
A user can upload 2D and 3D models of tissues, as required for a given simulation, from a personal computer or handheld device, as shown in the screen shot of
Once running on the simulating system computer, the tissue may be rotated for viewing on a display at any user-desired angle, and tissue may be “cut away” so that electrical activity may be viewed from within the 3D structural model of the tissue. An example of a cutaway view with electrical activity displayed is provided in the screen shot of
In one embodiment, the model includes such simplification of electrical transport mechanism in tissue elements and between adjacent tissue elements that the processor can provide for displaying electrical activity moving through the heart muscle in a time approximately equal to actual propagation time. In one embodiment, the simplification of computational steps to simulate propagation involves a linear approximation of the equation that updates the internal state of each tissue element. This vastly increases speed compared to published computational models that use more complicated functions than a linear approximation to simulate electrical propagation in cardiac tissue.
The model of electrical tissue activation may be run in real-time, slow motion, faster than real-time or stopped at any time during the simulation.
In one embodiment, stimulating and recording electrodes in the model may be placed at any user-desired (arbitrary) location in and around the tissue. For example, for the planar modeled tissue of
In one embodiment, the model includes a set of parameters for conduction within each tissue element and a difference parameter, such as electrical resistance, for conduction between tissue elements. Each of these parameters may be displayed in color coded fashion. In one embodiment, as tissue is stimulated by a virtual electrical input from an electrode, a colored wave front moves through the tissue simulation over time. In this embodiment, each specific color represents a specific voltage level. Thus, the display demonstrates all the tissue elements that are at the same time voltage at the same time (i.e. representative of isopotential activation).
A screen shot from a 3D heart model showing stimulation of the tissue initiated from an electrode located at the tip of a catheter placed at a user-controlled location relative to the tissue is shown in
A screen shot of two simulated catheters located at a ninety degree angle to one another on electrically excitable planar tissue is shown in
A screen shot from the 3D heart model with multiple electrodes and multiple catheters is shown in
In one embodiment, the model simulates ablation of tissue, removing excitability of a tissue element and/or electrically disconnecting one or more tissue elements from neighboring tissue elements. This is equivalent to setting the “aliveness” property to false. The model enables a user to observe the flow of electrical activity through the tissue before and after ablation and to observe how ablation of a particular region affects the relative timing of deflections recorded in an EGM, tissue activation times, and relative amplitudes of electrical activity.
A screen shot showing ablation of tissue from the tip of a catheter is shown in
One application of the model provided in the present patent application is to enable understanding of complex heart muscle reentrant rhythms that may be aperiodic or that manifest as complex sequences of wave collisions and wave breaks. Ultimately, any arrhythmia due to such reentry of electrical excitation will involve the continuous propagation of at least a single wave of excitation, though it may split off into daughter waves or collide with other waves in the process. Before the present patent application, identifying the pathways of these reentrant waves was a near impossible task for the human eye.
One embodiment of the present patent application provides a method for tracking excitation waves through time in two steps. First, contiguous waves are identified in sequential frames (time steps). A sample frame with identified contiguous wave fronts is shown in
In one embodiment, the model provides a batching capability that allows a user to run many simulations in parallel or in series with no additional input from the user once the first process is initiated. In this embodiment, each simulation can record user specified data to a local or network storage resource for further data observation or manipulation.
In one embodiment real clinical environments are simulated in the model. In one embodiment, an X-Ray view is produced in the simulation, as shown for a planar tissue in
In another embodiment, electroanatomic mapping is simulated in the model. In this embodiment, a user may specify a reference electrode and a roving electrode. The relative timing between signals from these electrodes is used along with the location of the roving electrode to build an isochronal map of tissue activation. A 3 point sample of an isochronal map on a planar tissue is shown in
In another embodiment a real isochronal map is calculated based on the simulation produced by the model when given specific parameter values. This allows a user to compare the accuracy of the map produced manually using the roving electrode to the theoretical solution. The real isochronal map is calculated and displayed in
In one embodiment a fully functional stimulator is included in the simulator, as shown in
In one embodiment, a user controls the location of electrodes and catheters by moving a computer input device, such as a trackpad or mouse. This allows simulations to run on personal computers and other devices that are controlled through user gestures.
In another embodiment, a digital interface is included that allows third party systems to read data simulated by the model of electrically excitable tissues. A module is included that formats output of the simulation so that it can be input to a third party device that normally takes data coming from a real heart.
Magnetic tracking devices designed for tracking the location of catheters within the body are currently in production by Ascension Technology Corporation of Milton, Vermont. These trackers use small orthogonal coils located on the catheter to report the incident EM wave signals. The signals are produced by a stationary or wearable EM field source. From the coil data, the orientation and position of the catheter relative to the source may be calculated. Provided that the location of the source with respect to the tissue is known, the location of the catheter relative to the tissue is also known. These data can be input to our model of electrical activity of the tissue.
Thus, a user may move an actual catheter (as opposed to a computer input device, such as a trackpad or mouse) inside a simulated subject and simulated heart. Once inside the simulated physical representation of the heart, the location data would be sent to the model. The present model can then be run by the user on a computer as if the catheter were located in an actual subject. Thus, a user uses the model to experience replicating all the conditions that would be encountered in a clinical setting.
In another embodiment, the virtual position of the catheter in the present simulation is determined based on integrating data from a commercially available haptic control of the catheter—as if a physical catheter were present within a physical body (herein referred to as a haptic interpretation unit). Such a commercially available haptic control simulator is currently available under the trade name ANGIO Mentora by Simbionix USA of Cleveland, Ohio and Simbionix Ltd of Airport City, Israel. These haptic control simulators can provide a visual simulation of the 3D heart tissue, with views that represent ultrasound visualization as well as fluoroscopy visualization. The haptic control simulators do not provide any information on the electrical activity of the simulated tissue, and thus are of limited utility for electrophysiology training and education.
In one embodiment, the present electrical model of excitable tissue includes an open architecture interface that supports third party catheter manufacturers as well as firms that produce simulations of the physical properties of catheters and tissues. In one embodiment the model includes a digital communications protocol that these third parties may use to provide instruction to the simulation. A hard wired Ethernet (TCP/IP) digital interface is shown, however, other serial interfaces could be accommodated, including serial (USB, RS-232, RS-485, RS-422) and wireless Ethernet (802.11), Bluetooth (802.15), or Zigbee (802.15.4) and others.
In this embodiment, the third party provides the position and orientation data of the catheter or electrodes relative to the heart over the digital interface. A separate, dedicated personal computer or dedicated microprocessor is used to run the electrical simulation of the tissue using the position and orientation data of the catheter or electrodes relative to the heart provided from the third party and to support user controlled functions such as the display of EGMs.
A functional block diagram showing how the third party systems would interface to the present model of electrically excitable tissues of the present patent application is shown in
In one embodiment, the electrical model of excitable tissue of the present application includes an open architecture interface to support third party electrophysiologic, electroanatomic or anatomic imaging system manufacturers (for example, x-ray systems, electrogram recording systems, ultrasound systems and 3D electroanatomic recording systems). In this embodiment, electrical and anatomic/location data is exported from the present model over a digital communications port. In one use, a trainee can view electro-anatomic data without requiring the use of living, electrically excitable tissue or “canned” prerecorded EGM data. Users can control their own experience and learn by moving the catheters and electrodes as they would in the clinical setting. The users can decide where to place electrodes and catheters, decide on a course of action, and ablate the tissue, all within the model of the present patent application, then see the result of their training session on a third party's display.
Input Protocol: In one embodiment, catheter electrode position and orientation are input via Transmission Control Protocol (TCP) and Internet Protocol (IP). Third party software which transmits digital data to the specified host address and in the appropriate formats may modify the position and orientation of specific catheter electrodes within the Visible EP software environment at run-time. Tables 1 and 2 contain the packet formats and their respective functions. All multi-byte values are entered in little-endian format. Floating point values follow the IEEE Standard for Float-Point Arithmetic (IEEE 754) for single-precision floating point representations.
In one embodiment, the model of the present patent application moves the electrode identified by the specified ID to the location defined by {x, y, z} in its coordinate space. This implies that the third party system supplying this information has knowledge of the model's coordinate system beforehand.
In one embodiment, the electrode identified by the specified ID is oriented such that the catheter shaft leading away from it will do so in the direction defined by {Nx, Ny, Nz} in its coordinate space. This implies that the third party system supplying this information has knowledge of the model's coordinate system beforehand, though the scale of the {Nx, Ny, Nz} vector is irrelevant.
These orientation data can also be provided as an orientation matrix or a quaternion, in the case where axial rotation of a catheter is relevant.
Output Protocol: In one embodiment, data is output from the simulation in order to emulate data coming from a real patient in a clinical environment. This is performed by a modular translation unit that converts the data stored internally by the model simulation to the appropriate format for the specific third party system connected for receiving this data. In this case, a customized translation unit is developed or provided for the particular third party system.
In one embodiment, software configurable panels provide the users with capability to change values of key operational parameters, as shown in screen shots in
The user programmable tissue creation window shown in
Each tissue element's state is defined by two variables, potential (or voltage) and phase. In the model, tissue elements of the heart can be in one of several different phases, including Rest, Upstroke, Plateau, Repolarization, and Relative Refractory, as shown in Table 3. Phase is what determines which part of the piece-wise linear function an element is operating in. The behavior of a tissue elements potential in the various phases is shown in
In the model, tissue elements of the heart also have tunable values of each of parameters, including the following parameters, as shown in Table 4: activation threshold, activation rate, plateau potential, plateau time, repolarization rate, resting potential, restitution slope, restitution factor, minimum activation slope, minimum plateau time, maximum repolarization rate, aliveness, type of element (pacemaker), spontaneous depolarization rate, and leak potential. For aliveness and type of element (pacemaker) the values are Boolean--true or false.
In performing the simulation the processor running the model starts, as shown in box 100 by first updating each tissue element potential by diffusion, such as via Ohm's law, as shown in box 101 of
The processor then updates each tissue element internally, as shown in box 102 of
For calculations within each tissue element the processor follows a process as illustrated in
When the processor finds an element that is alive, the processor checks whether the phase is Rest, as shown in box 116. If so, the processor then determines whether the element is a pacemaker, as shown in box 117. If so, the processor sets the new voltage to be equal to the old voltage plus an increment for depolarization, as shown in box 118. The processor then checks whether the voltage is greater or equal to a threshold, as shown in box 119. If so, the processor changes the phase to upstroke, as shown in box 120 and in
If the processor finds that the phase is not Rest in box 116, the processor then determines whether the phase is Upstroke, as shown in box 121. If so, the processor sets the new voltage to be equal to the old voltage plus an increment for upstroke, as shown in box 122. The processor then checks whether the voltage is greater or equal to the plateau voltage, as shown in box 123. If so, the processor changes the phase to plateau, as shown in box 124.
If the processor finds that the phase is not upstroke in box 121, the processor then determines whether the phase is Plateau, as shown in box 125. If so, the processor sets the new voltage to be equal to Vplateau, as shown in box 126. The processor then checks whether a time equal to Tplateau has elapsed, as shown in box 127. If so, the processor changes the phase to repolarization, as shown in box 128.
If the processor finds that the phase is not Plateau in box 125, the processor then determines whether the phase is Repolarization, as shown in box 128. If so, the processor sets the new voltage to be equal to the old voltage plus an increment for repolarization, as shown in box 129. The processor then checks whether the voltage is greater or equal to a threshold, as shown in box 130. If so, the processor changes the phase to relative refractory, as shown in box 131.
If the processor finds that the phase is not Repolarization in box 128, the processor then determines whether the phase is relative refractory, as shown in box 132. If so, the processor sets the new voltage to be equal to the old voltage minus an amount for repolarization, as shown in box 133. The processor then checks whether the voltage is less than or equal to Vrest, as shown in box 134. If so, the processor changes the phase to rest, as shown in box 135. The processor then checks whether the voltage is greater than or equal to a threshold, as shown in box 136. If so, the processor applies restitution (see table 6) and sets the phase to Upstroke, as shown in box 137.
The step after each of the above checks whether this is the last element, and if so ends processing. If not the processor gets the next element and the process starts again.
Upon starting the software, the user is presented with a splash page shown in
In the didactic mode of the software, the user may progress through a module of educational material presented as a combination of text and image based slides (
In the laboratory mode of the software, the user is able to load existing parameters configurations (e.g.
Aspects of certain embodiments of the present patent application include:
While several embodiments, together with modifications thereof, have been described in detail herein and illustrated in the accompanying drawings, it will be evident that various further modifications are possible without departing from the scope of the invention as defined in the appended claims. Nothing in the above specification is intended to limit the invention more narrowly than the appended claims. The examples given are intended only to be illustrative rather than exclusive.
Number | Date | Country | |
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61801900 | Mar 2013 | US |