Abstract:
A patient monitor for determining a probability that a patient has acute cardiac ischemia including an input device connectable to a patient to acquire electrocardiogram (ECG) signals from the patient, an instrumentation amplifier connected to the input terminal to combine the signals and to generate at least one ECG lead, and an analysis module. The analysis module is operable to continuously read the ECG lead, to analyze a portion of the ECG lead for a period of time, and to calculate a probability that the patient has acute cardiac ischemia based at least in part on the analyzed portion of the ECG lead.

Description:
BACKGROUND OF INVENTION 
     The invention relates to a patient monitor and, particularly, a patient monitor for continuously monitoring one or more physiological signals of a patient and for determining a probability that a patient has acute cardiac ischemia based at least in part on one of the continuously monitored physiological signals. 
     Every day, patients arrive at an emergency room of a hospital complaining of chest pain. The chest pain may be a symptom indicating the patient is experiencing a myocardial infarction or, alternatively, the chest pain may be a symptom indicating the patient is experiencing a lesser medical condition (e.g., heartburn or indigestion). Statistics show that quickly identifying whether a patient is having a myocardial infarction may minimize the amount of damage to the heart. However, performing the necessary tests to correctly determine whether a patient is experiencing the myocardial infarction or heartburn are expensive. 
     One instrument used to predict whether a patient is likely experiencing a myocardial infarction is an electrocardiograph capable of calculating a probability that the patient has acute cardiac ischemia. If the patient has a high probability of acute cardiac ischemia, then the patient should be further tested to determine whether the patient is experiencing a heart attack. One instrument for determining a probability of a patient having acute cardiac ischemia is an Acute Cardiac Ischemia—Time-Insensitive Predictive Instrument (ACI-TIPI). ACI-TIPI is described in detail in Selker et al., H. P.  A Tool for Judging Coronary Care Unit Admission Appropriateness, Valid for both Real - Time and Retrospective Use: Medical Care,  VOL. 29, No. 7 July 1991), pp. 610-627 and Selker et al., H. P.  Erratum: Medical Care,  Vol. 30, No. 2 (February 1992), p. 188, both of which are incorporated herein by reference. 
     The ACI-TIPI calculates a score representing the probability of a patient having acute cardiac ischemia. Based on the probability of the patient having acute cardiac ischemia, an experienced doctor or technician can determine whether the patient should be admitted to the coronary care unit. Once admitted to the coronary care unit, the patient can undergo more complicated, expensive and time consuming tests to determine whether the patient is experiencing a heart attack. 
     Prior medical equipment having the capability of calculating a probability of a patient having acute cardiac ischemia consisted exclusively of electrocardiographs having ACI-TIPI. An example electrocardiograph capable of determining a probability that a patient has acute cardiac ischemia is the MAC™5000, which is manufactured and sold by GE Medical Systems Information Technologies, Inc. Electrocardiographs are not used for continuous, constant or ongoing patient monitoring, i.e., they typically only take a small time sample (e.g., ten to twelve seconds) of a patient&#39;s electrocardiograms (ECGs). A separate piece of medical equipment (i.e., a patient monitor) is attached to a patient for continuous, constant or ongoing monitoring of patient parameters. One such patient monitor is the DASH®2000 brand patient monitor, which is manufactured and sold by GE Medical Systems Information Technologies, Inc. Such patient monitoring devices however have not heretofore included the capability of determining the probability that a patient has acute cardiac ischemia. 
     SUMMARY OF INVENTION 
     When the patient enters the emergency room complaining of chest pains, multiple pieces of medical equipment (e.g., a patient monitor and an electrocardiograph) may be attached to the patient at any time. Attaching multiple pieces of equipment to the patient requires time for attachment, space for each piece of equipment, and coordination among the emergency room staff. In addition, the patient may be periodically moved throughout the emergency room or the hospital. Consequently, requiring an electrocardiograph to be temporarily attached to the patient requires use of extra time, space, personnel, and restricts transferability, which may affect the care provided to the patient. Therefore, it would be beneficial to have a patient monitor, and particularly a patient transport monitor, capable of determining a probability that a patient has acute cardiac ischemia. 
     Accordingly, the invention provides a patient monitor for determining a probability that a patient has acute cardiac ischemia. The patient monitor includes an input device connectable to a patient to continuously acquire electrocardiogram (ECG) signals from the patient, an instrumentation amplifier connected to the input terminal to combine the signals and to generate at least one ECG lead, and an analysis module. The analysis module is operable to continuously read the ECG lead, to analyze a portion of the ECG lead for a period of time, and to calculate a probability that the patient has acute cardiac ischemia based at least in part on the analyzed portion of the ECG lead. 
     The invention further provides a method of determining a probability that a patient has acute cardiac ischemia. The method includes the acts of providing a patient monitor having an input device connectable to a patient, acquiring electrocardiogram (ECG) signals from the patient, generating at least one ECG lead in response to acquiring the ECG signals, continuously monitoring the ECG lead, analyzing a portion of the ECG lead for a period of time, and calculating the probability that the patient has acute cardiac ischemia based at least in part on the analyzed portion of the ECG lead. 
     The invention further provides a software program for a patient monitor. The software program is capable of determining a probability that a patient has acute cardiac ischemia. The software program includes the acts of reading at least one electrocardiogram (ECG) lead acquired from the patient, continuously monitoring the ECG lead, analyzing a portion of the ECG lead for a period of time, and calculating the probability that the patient has acute cardiac ischemia based at least in part on the analyzed portion of the ECG lead. 
     Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a schematic diagram of a patient monitor embodying the invention. 
     FIG. 2 is a flowchart implementing a method of determining a probability that a patient has acute cardiac ischemia. 
    
    
     DETAILED DESCRIPTION 
     Before one embodiment of the invention is explained in full detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of including and comprising and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
     A patient monitor  100  embodying the invention is schematically shown in FIG.  1 . An example monitor embodying the invention is a GE Medical Systems Information Technologies, Inc. DASH®3000 Pro™ brand portable monitor. In general terms, the monitor  100  includes one or more input devices  105 , a central unit  110 , a data entry device  115  connected to central unit  110 , and one or more output devices  120  connected to central unit  110 . 
     The one or more input devices  105  include a plurality of electrodes E 1 , E 2  . . . E n  that are connectable to a patient. The electrodes acquire electrical activity (i.e., ECG signals) generated by the patient. The number of electrodes E 1 , E 2  . . . E n  may vary. But for the embodiment shown, the number of electrodes is equal to ten and are connected to the patient in a standard twelve-lead configuration. 
     The electrodes E 1 , E 2 . . . E n  are connected to the central unit  110  by an interface cable  125 . The interface cable  125  provides direct communication between the electrodes E 1 , E 2  . . . E n  and an input terminal  130 . The interface cable  125  allows for transmission of the acquired ECG signals from the patient to the central unit  110 . The interface cable  125  is preferably a passive cable but, alternatively, the cable  125  may contain active circuitry for amplifying and combining the ECG signals into ECG leads (discussed further below). In other embodiments, the electrodes E 1 , E 2  . . . E n  may be in communication with the central unit  110  through a telemetry-based transmitter transmitting a radio frequency (RF) signal to one or more antennas connected to central unit  110  through a conventional RF receiver. 
     The one or more input devices  105  may further include one or more sensors S 1 , S 2  . . . S n . The sensors S 1 , S 2  . . . S n  are connectable to the patient and acquire physiological signals from the patient. Example sensors may include invasive and noninvasive blood pressure sensors, carbon dioxide sensors, pulseoximetry sensors, temperature sensors, etc. Similar to electrodes E 1 , E 2  . . . E n  and for the embodiment shown, the one or more sensors S 1 , S 2  . . . S n  are connected to the central processing unit at input terminals  135  by interface cables  140 . In other embodiments, the one or more sensors may be in communication with the central processing unit via a telemetry transmitter as described above. 
     The data-entry device  115  allows an operator (e.g., a technician, nurse, doctor, etc.) to enter data into the central unit  110 . The data-entry device  115  may be incorporated within the central unit  110  (e.g., a trim knob) or, alternatively, may be a stand-alone device (e.g., a stand-alone keyboard). Example data-entry devices  115  include a trim knob, a keyboard, a keypad, a touch screen, a pointing device (e.g., a mouse, a trackball), etc. 
     The central unit  110  includes a power supply  147 . The power supply  147  powers the patient monitor  100  and receives input power either by an external power source  155  or an internal power source  160  (e.g., a battery). 
     The central unit  110  also includes amplifying-and-filtering circuitry  165 , analog-to-digital (A/D) conversion circuitry  170 , and an analysis module  175 . The amplifying-and-filtering circuitry  165 , the A/D conversion circuitry  170 , and the analysis module  175  may be discrete circuitry, may be incorporated as an integrated circuit (e.g., an application specific integrated circuit), or may be a combination of both. 
     The amplifying-and-filtering circuitry  165  receives the physiological signals from the input terminals  130  and  135 , and amplifies and filters (i.e., conditions) the physiological signals. For example, the amplifying-and-filtering circuitry  165  includes an instrumentation amplifier  180 . The instrumentation amplifier  180  receives the ECG signals, amplifies the signals, and filters the signals to create a multi-lead ECG. The number of leads of the multi-lead ECG may vary without changing the scope of the invention. 
     The A/D conversion circuitry  170  is electrically connected to the instrumentation amplifier  180 . The A/D conversion circuitry  170  receives the amplified and filtered physiological signals and converts the signals into digital physiological signals (e.g., a digital multi-lead ECG.) The digital physiological signals are then provided to the analysis module  175  which is electrically connected to the A/D conversion circuitry  170 . 
     The analysis module  175  reads the digital physiological signals, analyzes the signals from the A/D conversion circuitry  170 , and displays the signals and the resulting analysis to an operator. The analysis module  175  includes a controller or microprocessor  182  and internal memory  185 , and implements a software program to control the monitor  100 . The internal memory  185  includes program storage memory  190  for storing the software program and data storage memory  195  for storing data. The implementation of the software program, including determining a probability that the patient has acute cardiac ischemia, is discussed in further below. 
     The output devices  120  may include a printer, a display, a storage device (e.g., a magnetic disc drive, a read/write CD-ROM, etc.), a server or other processing unit connected via a network  200 , and a speaker. Of course, other output devices may be added or attached (e.g., a defibrillator), and/or one or more output devices may be incorporated within the central unit  110 . Additionally, not all of the outputs  120  are required for operation of the monitor  100 . 
     In operation and at act  300  (FIG.  2 ), an operator activates the monitor  100 . The software initializes the microprocessor  182 . The operator then attaches the electrodes E 1 , E 2  . . . E n  and/or sensors S 1 , S 2  . . . S n  to the patient. 
     At act  305 , the monitor  100  automatically identifies which input devices  105  are connected to the patient. Alternatively, the operator may inform the monitor  100 , via the data-entry device  115 , which inputs  105  are connected to the patient. Once the monitor  100  is informed from which inputs  105  to acquire physiological signals from, the monitor  100  begins continuously monitoring the physiological signals from the patient. The monitoring data may be displayed on the display, printed by the printer, stored in the data storage memory for analysis or later recall, provided to the external storage device for storage, and/or provided to the server via the network  200 . 
     For example and in the embodiment shown, the operator attaches ten electrodes to the patient and selects twelve-lead ECG monitoring. Once twelve-lead ECG-monitoring is selected (act  310 ), the monitor  100  continuously monitors the ECG leads generated by the patient (act  315 ). This is accomplished by acquiring electrical activity generated by the patient in the form of ECG signals. The ECG signals are transmitted to the input terminal  130  via the interface cable  125 . The ECG signals enter the central unit  110  at terminal  130  and are provided to the instrumentation amplifier  180 . The instrumentation amplifier  180  combines, amplifies and filters the ECG signals resulting in a standard twelve-lead ECG. For other electrode configurations, the number of leads of the multi-lead ECG may vary. The resulting multi-lead ECG is provided to the A/D conversion circuit  170 . The A/D conversion circuit  170  samples each lead of the multi-lead ECG to create a digital signal representing the multi-lead ECG, and provides the digital multi-lead ECG to the analysis module  175 . The analysis module  175  reads the digital multi-lead ECG signal for monitoring. The monitored twelve-lead ECG may be used to calculate a heart rate, detect an arrhythmia, measure ST-segment elevation and, as is discussed below, calculate a probability that the patient has acute cardiac ischemia. The monitor  100  continues to monitor the twelve-lead ECG until the operator exits the twelve-lead monitoring function (act  320 ). Other monitoring applications are performed similarly. The other monitoring applications include blood pressure monitoring, pulse oximetry monitoring, temperature monitoring, etc. 
     If the patient complains of heart pain, the operator may request the monitor  100  to perform a calculation of a probability that the patient has acute cardiac ischemia (act  325 ). For example, when a patient enters the emergency room complaining of heart pain, the emergency room staff may attach the patient monitor  100  to the patient for monitoring. In addition, a staff member (e.g., the resident emergency room doctor) may request a test to determine whether the patient has acute cardiac ischemia. In the past, an electrocardiograph and a technician would need to be requested and brought into the patient&#39;s direct area. The electrocardiograph would then need to be attached to the patient. Attaching the electrocardiograph to the patient takes valuable time. Moreover, the presence of another piece of equipment and the operator thereof connected to the patient, may inconvenience the emergency room staff. Thus, it is beneficial for the patient monitor  100  already connected to the patient for continuous, ongoing monitoring to be able to perform this function in addition to performing the monitoring function. 
     For the embodiment shown, the operator uses the data entry device  115  (e.g., the trim knob) to select an ACI-TIPI analysis. Once the ACI-TIPI analysis is selected (act  325 ), the software initiates an ACI-TIPI analysis subroutine (act  330 ). Although the patient monitor  100  described herein uses ACI-TIPI to determine a probability that the patient has acute cardiac ischemia, other instruments (i.e., formulas) may be used. 
     Specifically, the monitor  100  uses Formula 1 (below) to calculate or determine a probability that a patient has acute cardiac ischemia. 
     FORMULA 1 ACI-TIPI          probability                                %     =     100   ×     [     1   -     1     1   +     exp        (       b   o     +     ∑       b   i     ·     x   i           )             ]                              
     where: b o  is a constant term, b i  are coefficients, and x i  are variables. The coefficients include values representing a chest pain condition, patient demographics, and ECG analysis coefficients. The variables are empirically found and act as multipliers. Formula 1 and its constant term, coefficients and variables are further described in Selker et al.,  A Tool for Judging Coronary Care Unit Admission Appropriateness, Valid for both Real - Time and Retrospective Use: Medical Care,  Vol. 28, No. 7 (July 1991), pp. 610-627 and Selker et al.,  Erratum: Medical Care,  Vol. 30, No. 2 (February 1992), p. 188, both of which are incorporated herein by reference. 
     If the ACI-TIPI subroutine is selected, the patient monitor  100  proceeds to act  330 . At act  330 , the operator enters patient information. For example, the operator enters patient biographical data (e.g., patient sex and patient age) and a patient condition (e.g., chest or left arm pain is the primary complaint, chest or left arm pain is the secondary complaint, or chest or left arm pain is not present). As described above, the entered patient information is used by Formula 1 for determining a probability that a patient has acute cardiac ischemia. Other patient data may be entered when using different instruments. 
     Once the patient information is entered, the operator initiates the ACI-TIPI analysis (act  340 ) via the data entry device  115 . At act  345 , the software temporarily stores a portion of the monitored ECG leads for a period of time (i.e., a time window). When the ECG leads are stored, the software analyzes the stored ECG leads to obtain ECG analysis coefficients for the ACI-TIPI formula. Example ECG analysis coefficients include whether ECG Q-waves are present, whether the ECG ST segment is depressed or elevated by an amount, whether the ECG T-waves are inverted by an amount, and whether both the ECG ST segment is depressed and the ECG T-wave is inverted. The ECG analysis coefficients are used by Formula 1 to determine a probability that the patient has acute cardiac ischemia. Other ECG analysis coefficients may be used when using different instruments (i.e., different formulas). Additionally, the temporarily stored portion of the monitored ECG leads may be stored prior to the operator initiating the ACI-TIPI analysis. For example, the software may repeatedly store a portion of the monitored ECG leads for a period of time. Once the operator initiates the ACI-TIPI analysis, the software analyzes the most recently stored data to obtain ECG analysis coefficients for the ACI-TIPI formula. 
     At act  350 , the software calculates a probability that the patient has acute cardiac ischemia using the ACI-TIPI formula as is disclosed in Selker et al.,  A Tool for Judging Coronary Care Unit Admission Appropriateness, Valid for both Real - Time and Retrospective Use: Medical Care,  Vol. 28, No. 7 (July 1991), pp. 610-627 and Selker et al.,  Erratum: Medical Care,  Vol. 30, No. 2 (February 1992), p. 188. Upon completing the calculation, the resulting probability is disclosed (e.g., displayed on the monitor) to the operator (act  355 ). In addition, the software may provide a list of factors affecting or reasons for the resulting calculated probability. Example factors are shown in TABLE 1 EXAMPLE FACTORS. Based on the probability and disclosed factors (if provided), an experienced operator may determine whether the patient should be admitted to the cardiac care unit for further testing. In addition, the resulting probability and data used for calculating the probability may be stored or printed for future reference, or provided to the network  200  for additional analysis by a remote server or processor. 
     
       
         
               
             
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 EXAMPLE FACTORS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                  1. 
                 Chest or left arm pain present. 
               
               
                  2. 
                 Chest or left arm pain is chief complaint. 
               
               
                  3. 
                 Patient is male, less than 41 years of age. 
               
               
                  4. 
                 Patient is male, age 41-50. 
               
               
                  5. 
                 Patient is male, over 50 years of age. 
               
               
                  6. 
                 Patient is female, less than 41 years of age. 
               
               
                  7. 
                 Patient is female, age 41-50. 
               
               
                  8. 
                 Patient is female, over 50 years of age. 
               
               
                  9. 
                 Q waves are not present. 
               
               
                 10. 
                 No significant Q waves detected. 
               
               
                 11. 
                 ST segment is elevated 2 mm or more. 
               
               
                 12. 
                 ST segment is elevated 1-2 mm. 
               
               
                 13. 
                 ST segment is depressed 2 mm or more. 
               
               
                 14. 
                 ST segment is depressed 1-2 mm. 
               
               
                 15. 
                 ST segment is depressed 0.5-1 mm. 
               
               
                 16. 
                 No abnormal ST segment deviation detected. 
               
               
                 17. 
                 Hyperactive T-waves. 
               
               
                 18. 
                 T waves are inverted 5 mm or more. 
               
               
                 19. 
                 T waves are inverted 1-5 mm. 
               
               
                 20. 
                 Flattened T waves in all frontal or precordial leads. 
               
               
                 21. 
                 No T-wave abnormality detected. 
               
               
                   
               
             
          
         
       
     
     As can be seen from the above, the invention provides a patient monitor for determining a probability that a patient has acute cardiac ischemia. The invention also provides a method of determining a probability that a patient has acute cardiac ischemia and a software tool for a patient monitor to calculate a probability that a patient has acute cardiac ischemia. Various features and advantages of the invention are set forth in the following claims.