Abstract:
A cardiac mapping system simulator comprising a microprocessor for simulating the electrical signal propagation of a heartbeat as it moves across the surface of a heart. A series of impulses that mimic the electrophysiological waveform are generated forming a two-dimensional map depicting heart activity. The series of pulses are generated in accordance with predetermined patterns and applied to the inputs of a cardiac mapping system or electrophysiology (E.P.) lab equipment in order to assess the operating condition of the cardiac mapping system or E.P. lab equipment prior to use on patients.

Description:
FIELD OF THE INVENTION 
     The present invention relates in general to electrical signal generating systems and more particularly to a cardiac mapping system simulator for generating a series of signals which simulate two-dimensional electrophysiological impulses. 
     BACKGROUND OF THE INVENTION 
     Medical analysis of the heart muscle has revealed that each normal heart contraction originates from an area in the upper right atrium called the sinus auricular node, and spreads in the form of a depolarization wave through the atrioventricular node, across the heart to the ventricular myocardium. The depolarization wave then spreads through the muscular tissue of the ventricle to cause the ventricle to contract for pumping blood through the arteries. 
     Thus, although normal contraction of the heart is referred to in common parlance as being a &#34;heartbeat&#34;, in actuality the contraction proceeds as a wave which travels across the surface of the heart. In the event that various cells within the heart tissue have been damaged, propagation of the depolarization wave across the heart may be obstructed. Furthermore, in the event that the cells in a specific region of the heart have been damaged, conflicting depolarization waves may be generated by the affected cells which interfere with the normal heart rhythm, a condition known as cardiac arrhythmia. 
     The surgical treatment of cardiac arrhythmias has been facilitated by an understanding of the mechanisms of arrhythmia gained through a precise description of the structure and function of the cardiac tissues. To this end, advances in medical technology have resulted in development of various devices for investigating electrical activity, and thereby interoperatively identifying the sources of cardiac arrhythmias within a patient. 
     One such developmental tool is known as a cardiac mapping system comprising an electrode array having a plurality of electrodes arranged in a three-dimensional grid, a plurality of preamplifier units for amplifying signals received from the electrode array, a data acquisition sub-system for performing analog-to-digital conversion of the signals received from the preamplifier units, and an analysis and display processor for displaying individual epicardial waveforms as they propagate across the heart during each contraction. 
     In operation, the chest cavity of a patient is opened and the electrode array is located over or within the heart muscle. The electrodes detect bioelectric phenomena of the heart muscle at their individual locations across the surface of the heart and in response generate corresponding analog-electrical impulses representative thereof. The analysis and display processor captures and processes the data received from the acquisition sub-system and displays the individual waveforms. The information is typically displayed on a colour monitor as well as remote monitors in the operating room in the form of an isochronal map. Preferably, the data from the electrodes are then stored on an optical disc or other suitable storage apparatus. 
     It is important that proper functioning of the cardiac mapping system be assessed prior to use on patients since interpretation of results in the operating theatre will determine the diagnosis and hence the procedure to be performed. 
     A number of prior art systems have been developed for generating signals which simulate various electrophysiological impulses. For example, U.S. Pat. No. 3,323,068 (Woods) discloses an electrocardiogram simulator for generating EKG waveforms of the human heart. The simulator according to this prior art patent generates a single pulse conforming to a standard idealized EKG wave in order to set up or trouble shoot EKG analysis equipment. 
     Similarly, U.S. Pat. No. 3,469,115 (Cartridge) discloses a cardiac waveform simulator for generating a pulse having a generally triangular shape and a rise time to fall time characteristic closely resembling the pulses of a human cardiac waveform. 
     U.S. Pat. No. 4,204,261 (Ruszala et al) teaches a complex analog signal generator for generating a complete complex waveform which is divided into a plurality of outputs for testing and calibrating various types of medical equipment such as electrocardiogram displays and blood pressure waveform displays. Related U.S. Pat. No. 4,205,386 (Ruszala et al) teaches an electrocardiographic and blood pressure waveform simulator device for simulating both electrocardiographic and blood pressure waveforms, with the beginning of the blood pressure waveform being delayed from the beginning of the electrocardiographic waveform so that the waves are provided in a time sequence corresponding to waveforms that would ordinarily be supplied by a live patient. 
     U.S. Pat. No. 4,352,163 (Schultz et al) discloses a vector-cardiogram simulator for generating three distinct waveforms for simulating electrical activity within the human heart along three separate axes. The three generated waveforms are applied to the input of a vector-cardiogram machine for the purpose of calibration and testing. 
     The above discussed prior art patents all relate to systems for generating analog signals representative of electrophysiological activity in a single dimension with respect to time. A typical display output for such prior art systems would be in the form of a graph depicting electrical amplitude on one axis versus time on the other axis. Thus, such prior art systems provide signals which simulate the electrophysiological characteristics of a heartbeat, but do not provide for simulation of electrophysiological waves in two dimensions with respect to time (i.e. a simulation of the depolarization wave which travels across the heart surface). 
     SUMMARY OF THE INVENTION 
     According to the present invention, apparatus is provided for generating a series of signals for simulating two-dimensional electrophysiological impulses. The generated signals appear on outputs of the apparatus which are arranged to form a two-dimensional array or grid conforming to the grid pattern of the electrode array used in the cardiac mapping system. The apparatus preferably includes microprocessor circuitry for generating signals of sufficient complexity in two dimensions to enable thorough testing of the cardiac mapping system. Other arrays may be configured as global, patching or bands for either the epicardial or endocardial surfaces. 
     It is typically necessary to generate a variety of maps in order to completely characterize the system and ensure correct functioning of each channel corresponding to a grid on the electrode array. Thus, the microprocessor circuitry allows for flexible programming to generate the various complex signal patterns corresponding to the isochronal maps. The patterns which are generated by the simulator preferably include vertical, horizontal and square isochronal maps. 
     It is believed that no cardiac mapping simulator has hitherto been developed for generating waveforms in the form of timed sequences of signals for simulating two-dimensional electrophysiological impulses. 
     According to the present invention, there is provided an apparatus for generating a two-dimensional pattern of timed simulated electrophysiological impulses for application to an electrophysiological impulse display device, comprising programmable circuitry for generating a succession of digital signals, a circuit for receiving the aforementioned succession of digital signals and in response generating a succession of output signals on predetermined outputs thereof, wherein the outputs are arranged to form a two-dimensional array, and circuitry for shaping the output signals to resemble electrophysiological impulses, whereby the succession of output signals forms a two-dimensional pattern of simulated electrophysiological impulses for application to the display device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be described in greater detail below in conjunction with the following drawings, in which: 
     FIG. 1 is a block diagram of a cardiac mapping system, 
     FIG. 2 is a perspective view of a cardiac mapping system electrode array mounted on a heart model and connected to an input portion of the cardiac mapping system, 
     FIGS. 3A and 3B are anterior and posterior views of an output map of the cardiac mapping system showing a vertical test map, 
     FIG. 4 is a perspective view of the cardiac mapping system simulator of the present invention connected to the input portion of the cardiac mapping system, and 
     FIGS. 5A and 5B are a schematic diagram of the cardiac mapping system simulator according to a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning to FIG. 1, a cardiac mapping system is shown in block diagram format comprised of an electrode array 1 incorporating a plurality of electrodes for detecting electrophysiological impulses and in response generating and transmitting analog impulse signals to preamplifier and filter circuitry 3. The preamplifier and filter circuitry 3 is typically located under the operating room table. The electrode array 1 is attached to a human (or animal) heart 5 in the manner shown with reference to FIG. 2. A bundle of wires extends from the individual electrodes of the electrode array to a connector of the preamplifier and filter circuitry 3. Analog signal outputs from the preamplifier and filter circuitry 3 are transmitted to a data acquisition computer 7 by means of a multiplexer 9. An analog display 11 is connected to the multiplexer 9 for generating an analog display of a pre-selected one or more of the multiplexed signals received from the preamplifier and filter circuitry 3. 
     The data acquisition computer 7 performs an analog-to-digital transformation of the signals received from multiplexer 9, and the digital data is transmitted for storage to an optical disc computer 13 and associated optical disc storage medium 15. The data from the electrodes is sampled by the optical disc computer at a rate of preferably 1,000 Hz per electrode with 12-bit resolution. 
     The digital data signals generated by the data acquisition computer 7 are also applied to a data processing computer 17 which captures a preferably 10-second segment of the data signals and in response displays individual epicardial waveforms. 
     The processed data from computer 17 can then be displayed on a colour monitor 19 as well as remote monitors in the operating room and at the location of the acquisition sub-system (e.g. via analog display 11). Upon capturing the data, an operator at the data processing computer 17 can review the individual waveforms or request a complete isochronal map as shown in FIG. 3. The map is displayed on the colour monitor 19 as well as being transferred to a colour ink-jet printer 21. 
     The data processing computer 17 is also typically provided with well known peripherals such as hard disc drive 23, floppy disc drive 25, mouse 27, terminal 29 and black-and-white printer 31. 
     Turning to FIGS. 3A and 3B, a typical isochronal map is shown as it would appear on colour monitor 19 and colour printer 21 with the exception that the graph of FIG. 3 is in black and white instead of colour. FIG. 3A represents the anterior view of the electrode array 1, while FIG. 3B represents a posterior view. The electrode array 1 is comprised of a plurality of spaced apart electrodes (e.g. from as few as 5 to as many as 265, or more). However, according to the embodiment illustrated, 56 epicardial electrodes 33-145 are arranged in seven rows by eight columns across the surface of the array 5, for detecting electrophysiological impulses at the heart&#39;s surface. 
     Time durations from a predetermined one of the electrodes, chosen as a &#34;Reference electrode&#34;, are measured to each of the other electrodes. These activation times are plotted on an outline of the heart and common activation times are connected in order to form isochronal lines (i.e. the lines of vertical shading in FIGS. 3A and 3B which correspond to respective colours in a colour isochronal map). 
     Solid black lines 147 indicate anatomical landmarks in the heart (e.g. coronary arteries). 
     FIG. 4 shows the cardiac mapping simulator 149 of the present invention connected to the preamplifier and filter circuitry 3 discussed with reference to FIGS. 1 and 2. The simulator 149 is provided with a start switch 151 for initiating simulation of two-dimensional electrophysiological impulses which are used to test the cardiac mapping system. 
     As shown in greater detail with reference to FIGS. 5A and 5B, the cardiac mapping system simulator incorporates a microprocessor 153 for generating a succession of digital signals according to a known pattern via outputs PA0-PA7 via data bus 154 to successive inputs of a plurality of (e.g. seven) output latches. For the purpose of illustration, only one of the output latches 155 is illustrated. Although not shown, the remaining six output latches are connected to data ports PAO-PA7 of microprocessor 153 via bus 154 in a manner identical to that shown with reference to output latch 155. 
     The microprocessor 153 is preferably a single-chip computer such as the Motorola MC68705R3S integrated HMOS microprocessor featuring on-board RAM, EPROM, bi-directional input/output lines, etc. An external crystal Xl is connected to the microprocessor for generating a system clock frequency of preferably 1 MHz resulting in an instruction cycle time of 4 microseconds. 
     The clock frequency is dictated by the crystal&#39;s resonating frequency. Capacitors C1 and C2 are coupling capacitors, while C3 provides a reset-delay at power ON. An LEDI may optionally be connected via terminals Jl-7 and Jl-8 to an input/output port PB4 of microprocessor 153 and via current limiting resistor R2 to the +5 volt power source for indicating when the simulator is activated. 
     The microprocessor 153, output latch 155 and other circuitry of the simulator is powered by means of a 9-volt battery 157 connected at terminals Jl-1 and Jl-2 to start switch 151, relay K1 and regulator 159 for generating a regulated 5-volt DC output to the various electronic components of the simulator. 
     Depression of the start switch 151 results in power being momentarily applied to power the microprocessor 153, thereby implementing an initialization routine. The initialization routine of microprocessor 153 causes a high-to-low logic transition on output PB5. This causes the Q0a output of a flip-flop 161 to go to a logic high level, thereby energizing the relay coil of relay K1 for Closing the relay contact and providing battery supply to the system. Three sections of the flip-flop 161 are connected in parallel to supply the current required by relay K1. The initialization routine also outputs a 100 msec pulse to trigger the cardiac mapping system via an output port PB3. 
     At the end of the map generation routines (discussed in greater detail below), the microprocessor 153 causes the PB5 output to go to a logic high level, thereby causing the Q0a output of flip-flop 161 to return to a logic low level, for opening the relay contact and disconnecting power from the system. 
     Thus, according to the circuit of the present invention, the mapping simulator does not consume any energy from battery 157 when it is not in use, thereby prolonging the operating life of the battery. 
     Input/output lines PB0-PB2 of microprocessor 153 are arranged as BCD (Binary Coded Decimal) outputs for driving a one-of-eight decoder 163. The X1-X7 outputs of decoder 163 are connected to respective clock inputs CK of the seven output latches. The X1-X7 outputs of decoder 163 are active high and are used to select individual ones of the output latches to receive data from microprocessor 153 via the respective D0-D7 inputs. 
     The data bus 154 connecting outputs PA0-PA7 of microprocessor 153 to respective data inputs D0-D7 of the seven output latches is also Connected Via a resistor array R7 to the +5-volt power source for ensuring proper tri-state impedance conditions when microprocessor 153 is not generating data for output via the PA0-PA7 terminals. Similarly, respective outputs X1-X7 of decoder 163 as well as outputs PB1 and PB2 of microprocessor 153 are connected to ground via a further resistor array R8, while output PB0 is connected to the logic high power source +5-volt via resistor R5. Resistor arrays R7 and R8 are preferably disposed within a single in-line package (SIP). 
     As indicated above, seven 8-bit output latches are provided for generating simulated electrophysiological signals corresponding to respective ones of the 56 electrodes 33-145. Data is presented to the output latches from the PA0-PA7 outputs of microprocessor 153 and an address signal is generated by microprocessor 153 on the PB0-PB2 outputs and is transmitted to the A, B and C inputs of decoder 163. The data from microprocessor 153 is clocked in to the respective output latches by means of a logic high level pulse from one of the X1-X7 outputs of decoder 163. 
     When all of the output latches contained the required data for application to the cardiac mapping system, the microprocessor 153 sets the PCO output thereof to a logic low level for simultaneously enabling the latches via the output enable inputs OE. The data signals are presented via output ports Q0-Q7 to a plurality of wave shaping circuits within a wave shaping board 165. 
     Each line from respective ones of the output latches is connected to a corresponding RC network within the wave shaping board 165 for attenuating and shaping the received digital pulse into a bipolar pulse of preferably 15 mV amplitude and 5 mS duration. The bipolar pulse waveform closely resembles the electrophysiological signals normally generated by the heart and received via the epicardial bipolar electrodes 33-145. 
     In accordance with the preferred embodiment, nine maps are generated by the simulator 147 with a 500-mS delay between each map. There is also preferably a 500-mS delay after execution of the last map and before the microprocessor 153 causes flip-flop 161 to open relay K1 for removing power from the simulator. 
     The vertical map illustrated in FIG. 3 may be generated by the simulator 149 of the present invention in accordance with a pattern of digital signals output from microprocessor 153 and written into respective ones of the output latches such as latch 155 in accordance with a sequence of loading respective ones of the latches as depicted diagrammatically in Table 1. 
     The latches are designated in Table 1 as latch No. 1 to latch No. 7, and the respective outputs Q0-Q7 of the latches are designated by the labels PA0-PA7 corresponding to the outputs of microprocessor 153. The numbers 1 through 8 shown in Table 1 represent successive instances in time during which respective digital pulses are output from latch No. 1-No. 7. 
     
                       TABLE 1______________________________________VERTICAL  PA0  PA1    PA2    PA3  PA4  PA5  PA6  PA7______________________________________LATCH #1 1      2      3    4    5    6    7    8LATCH #2 1      2      3    4    5    6    7    8LATCH #3 1      2      3    4    5    6    7    8LATCH #4 1      2      3    4    5    6    7    8LATCH #5 1      2      3    4    5    6    7    8LATCH #6 1      2      3    4    5    6    7    8LATCH #7 1      2      3    4    5    6    7    8______________________________________ 
    
     Thus, in operation, the first step in generating a vertical map comprises generation of eight digital output pulses within the PA0 bit location of each of the output latches and no pulses being generated in the remaining seven bits of each latch. This action causes eight of the 56 output lines from the simulator to present a pulse to the cardiac mapping system (corresponding to electrodes 33-45 shown in FIG. 3). 
     Next, eight digital output pulses are generated within the PAI bit location of each of the output latches and no pulses being generated in the remaining seven bits of each latch. 
     This procedure is repeated six more times for successive bits of the output latches (PA2 to PA7) resulting in digital simulation of a vertical map progressing from left to right across the electrode array. 
     Table 2 below indicates the correspondence between respective outputs of latch No.1-No. 7 in relation to the electrodes 33-145. 
     
                       TABLE 2______________________________________  PA0  PA1    PA2    PA3  PA4  PA5  PA6  PA7______________________________________LATCH #1 33     59     61   87   89   115  117  145LATCH #2 35     57     63   85   91   113  119  141LATCH #3 37     55     65   83   93   111  121  139LATCH #4 39     53     67   81   95   109  123  137LATCH #5 41     51     69   79   97   107  125  135LATCH #6 43     49     71   77   99   105  127  133LATCH #7 45     47     73   75   101  103  129  131______________________________________ 
    
     The simulator of the present invention preferably generates nine successive maps including the vertical map described in Table 1, and horizontal, all channels ON, centered square, logarithmic vertical bars, sequential channel firing, DL logo, checker board and cross maps as described in Tables 3-11 respectively, as follows: 
     
                       TABLE 3______________________________________HORIZONTAL  PA0  PA1    PA2    PA3  PA4  PA5  PA6  PA7______________________________________LATCH #1 1      1      1    1    1    1    1    1LATCH #2 2      2      2    2    2    2    2    2LATCH #3 3      3      3    3    3    3    3    3LATCH #4 4      4      4    4    4    4    4    4LATCH #5 5      5      5    5    5    5    5    5LATCH #6 6      6      6    6    6    6    6    6LATCH #7 7      7      7    7    7    7    7    7______________________________________ 
    
     
                       TABLE 4______________________________________ALL CHANNELS ON  PA0  PA1    PA2    PA3  PA4  PA5  PA6  PA7______________________________________LATCH #1 1      1      1    1    1    1    1    1LATCH #2 1      1      1    1    1    1    1    1LATCH #3 1      1      1    1    1    1    1    1LATCH #4 1      1      1    1    1    1    1    1LATCH #5 1      1      1    1    1    1    1    1LATCH #6 1      1      1    1    1    1    1    1LATCH #7 1      1      1    1    1    1    1    1______________________________________ 
    
     
                       TABLE 5______________________________________CENTRED SQUARE  PA0  PA1    PA2    PA3  PA4  PA5  PA6  PA7______________________________________LATCH #1 4      4      4    4    4    4    4    4LATCH #2 4      3      3    3    3    3    3    4LATCH #3 4      3      2    2    2    2    3    4LATCH #4 4      3      2    1    1    2    3    4LATCH #5 4      3      2    2    2    2    3    4LATCH #6 4      3      3    3    3    3    3    4LATCH #7 4      4      4    4    4    4    4    4______________________________________ 
    
     
                       TABLE 6______________________________________LOGARITHMIC VERTICAL BARS  PA0  PA1    PA2    PA3  PA4  PA5  PA6  PA7______________________________________LATCH #1 1      2      3    4    5    6    7    8LATCH #2 1      2      3    4    5    6    7    8LATCH #3 1      2      3    4    5    6    7    8LATCH #4 1      2      3    4    5    6    7    8LATCH #5 1      2      3    4    5    6    7    8LATCH #6 1      2      3    4    5    6    7    8LATCH #7 1      2      3    4    5    6    7    8______________________________________ 
    
     For the map pattern illustrated in Table 6, microprocessor 153 executes a delay subroutine for causing the delay time between loading of successive bit locations of the output latches to decrease in an exponential manner. 
     
                       TABLE 7______________________________________SEQUENTIAL CHANNEL FIRING  PA0  PA1    PA2    PA3  PA4  PA5  PA6  PA7______________________________________LATCH #1  1      2      3    4    5    6    7    8LATCH #2  9     10     11   12   13   14   15   16LATCH #3 17     18     19   20   21   22   23   24LATCH #4 25     26     27   28   29   30   31   32LATCH #5 33     34     35   36   37   38   39   40LATCH #6 41     42     43   44   45   46   47   48LATCH #7 49     50     51   52   53   54   55   56______________________________________ 
    
     
                       TABLE 8______________________________________DL LOGO  PA0  PA1    PA2    PA3  PA4  PA5  PA6  PA7______________________________________LATCH #1 2      2      2    2    2    2    2    2LATCH #2 2      1      1    2    2    1    2    2LATCH #3 2      1      2    1    2    1    2    2LATCH #4 2      1      2    1    2    1    2    2LATCH #5 2      1      2    1    2    1    2    2LATCH #6 2      1      1    2    2    1    1    2LATCH #7 2      2      2    2    2    2    2    2______________________________________ 
    
     
                       TABLE 9______________________________________CHECKER BOARD  PA0  PA1    PA2    PA3  PA4  PA5  PA6  PA7______________________________________LATCH #1 1      2      1    2    1    2    1    2LATCH #2 2      1      2    1    2    1    2    1LATCH #3 1      2      1    2    1    2    1    2LATCH #4 2      1      2    1    2    1    2    1LATCH #5 1      2      1    2    1    2    1    2LATCH #6 2      1      2    1    2    1    2    1LATCH #7 1      2      1    2    1    2    1    2______________________________________ 
    
     
                       TABLE 10______________________________________CROSS MAP  PA0  PA1    PA2    PA3  PA4  PA5  PA6  PA7______________________________________LATCH #1 4      3      2    1    1    2    3    4LATCH #2 3      3      2    1    1    2    3    3LATCH #3 2      2      2    1    1    2    2    2LATCH #4 1      1      1    1    1    1    1    1LATCH #5 2      2      2    1    1    2    2    2LATCH #6 3      3      2    1    1    2    3    3LATCH #7 4      3      2    1    1    2    3    4______________________________________ 
    
     Generation of the sequential pulse trains in Tables 3-10 is interpreted by the cardiac mapping system as being a timing map received from electrodes 33-145. Within the cardiac mapping system, each pulse is assigned an &#34;activation time&#34;. This &#34;activation time&#34; is assigned a colour in the output isochronal map. The mapping then creates a map by interpolating colours between the physical spatial location of the successive &#34;activation times&#34;. The data from the physical spatial location is obtained by the mapping system from the electrode grid. 
     As indicated above, there are preferably 9 maps which are generated successively by the simulator of the present invention for testing proper operation of the cardiac mapping system. These 9 maps are preferably executed every time the simulator is activated by depressing the start switch 151. An operator at the data processing computer 17 can choose to generate a particular map by selecting a specific pattern acquired by the mapping system. 
     The aforementioned nine maps are preferably generated in sequence and spaced approximately 0.5 seconds apart, in the following sequence: 
     1) All channels simultaneously ON (Table 4) 
     2) Linear Vertical Bars (Table 1) 
     4) Centred Square (Table 5) 
     5) Logarithmic Vertical Bars (Table 6) 
     6) Sequential Channel Firing (Table 7) 
     7) DL Logo (Table 8) 
     8) Checker Board (Table 9) 
     9) Cross (Table 10) 
     The microprocessor program for producing the various maps is presented as a source code listing in Appendix I, to which the reader is referred. 
     Other embodiments or variations of the present invention are contemplated, as follows. The simulator of the present invention may with minor software modifications be used to test equipment in an electrophysiology laboratory. The principal instrument requiring testing in such a laboratory is the amplifier system. The proper functioning of the amplifiers, switching system, digital conversion, etc. of such electrophysiological equipment can be tested with the simulator of the present invention by providing precisely time signals on each of the output channels. 
     Furthermore, automated systems for interpreting the data gathered by an electrophysiology laboratory system can be provided to receive time coded signals from the simulator in order to execute and test associated algorithms and check the results against known values. 
     All such variations and modifications are believed to be within the sphere and scope of the present invention as defined by the claims appended hereto.