System for the detection of cardiac events

Abstract

Disclosed is a system for the detection of cardiac events (a guardian system) that includes an implanted device called a cardiosaver, a physician's programmer and an external alarm system. The system is designed to provide early detection of cardiac events such as acute myocardial infarction or exercise induced myocardial ischemia caused by an increased heart rate or exertion. The system can also alert the patient with a less urgent alarm if a heart arrhythmia is detected. Using one or more detection algorithms, the cardiosaver can detect a change in the patient's electrogram that is indicative of a cardiac event within five minutes after it occurs and then automatically warn the patient that the event is occurring. To provide this warning, the guardian system includes an internal alarm sub-system (internal alarm means) within the cardiosaver and/or an external alarm system (external alarm means). If the guardian system is put into a pacemaker, the algorithm can utilize a different analysis of the electrogram depending on whether or not the pacemaker is actually pacing the heart.

1 . A system for detecting a cardiac event in a human patient the system including: 
 at least two sensors adapted to sense a signal resulting from the beating of the patient's heart;    an analog-to-digital converter coupled to the sensors for digitizing the signal, thereby producing a digital waveform;    a processor coupled to the analog to digital converter, the processor configured to: 
 (i) produce a plurality of segments from the digital waveform that are each at least one second long;  
 (ii) calculate a first value of a heart signal parameter within a first segment, wherein the first value is an average of the values of the heart signal parameter within the first segment;  
 (iii) calculate a second value of the heart signal parameter within a second segment;  
 (iv) calculate a first rate of change of the heart signal parameter based upon the first and second values of the heart signal parameter;  
 (v) control an operation of the system based on the first rate of change of the heart signal parameter.  
   
     
     
         2 . The system of  claim 1  wherein the sensors are electrodes.  
     
     
         3 . The system of  claim 2  wherein the electrodes are adapted for implantation into a body of the patient.  
     
     
         4 . The system of  claim 1  wherein the processor is further configured to produce baseline segments every 2*W seconds, and wherein the first segment is a baseline segment.  
     
     
         5 . The system of  claim 4  wherein W is at least 10 seconds.  
     
     
         6 . The system of  claim 4  wherein W is less than or equal to 12*60*60 seconds.  
     
     
         7 . The system of  claim 1  wherein the first and second segments are not consecutive segments.  
     
     
         8 . The system of  claim 7  wherein the processor is further configured to produce baseline segments every 2*W seconds, and wherein the first segment was produced U+/−W seconds before the second segment.  
     
     
         9 . The system of  claim 8  wherein U is greater than or equal to 60 seconds and less than or equal to 48*60*60 seconds.  
     
     
         10 . The system of  claim 1  wherein the processor is further configured to: (a) calculate a plurality of values of the heart signal parameter within the second segment; (b) based on the first value and the plurality of values of the heart signal parameter, calculate a corresponding plurality of rate of change values of the heart signal parameter; and wherein the first rate of change is one of the plurality of rate of change values.  
     
     
         11 . The system of  claim 1  wherein the processor is further configured to calculate Z values of the heart signal parameter within the second segment, where Z is greater than 1; and wherein the second segment has N beats; and wherein Z is less than N, so that the processor is configured to calculate the value of the heart signal parameter for less than all of the beats within the second segment.  
     
     
         12 . The system of  claim 1  wherein the processor is further configured to calculate a heart rate related heart signal parameter, and wherein the processor is further configured to control the operation of the system based on the value of the heart rate related heart signal parameter.  
     
     
         13 . The system of  claim 1  wherein the processor is further configured to calculate a heart rate related heart signal parameter, and wherein the processor is further configured to control the operation of the system based on the value of the heart rate related heart signal parameter, according to values of a lookup table which are associated with different heart rate ranges.  
     
     
         14 . The system of  claim 12  wherein the processor is compare the value of the heart rate related heart signal parameter to a threshold, and wherein the processor is further configured to control the operation of the system by initiating a prespecified action when the heart rate related signal parameter exceeds the threshold.  
     
     
         15 . The system of  claim 1  wherein the heart signal parameter pertains to ST segment shift.  
     
     
         16 . The system of  claim 1  further comprising an alarm subsystem, and wherein the operation of the system involves sending a command to the alarm subsystem to issue an alarm.  
     
     
         17 . The system of  claim 1  further comprising a housing adapted for implantation into a human body, and wherein the processor is disposed within the housing.  
     
     
         18 . A system for detecting a cardiac event in a human patient the system including: 
 at least two sensors adapted to sense a signal resulting from the beating of the patient's heart;    an analog-to-digital converter coupled to the sensors for digitizing the signal, thereby producing a digital waveform;    a processor coupled to the analog to digital converter, the processor configured to: 
 (i) produce electrogram segments from the digital waveform that are at least one second long;  
 (ii) calculate a first plurality of values of a heart signal parameter within a first segment;  
 (iii) calculate a second plurality of values of the heart signal parameter within a second segment that is produced after the first segment;  
 (iv) calculate a measure indicative of a rate of change of the heart signal parameter on a segment by segment basis, wherein the measure is based on the first and second pluralities of values of the heart signal parameter, and  
 (v) control an operation of the system based on the calculated rate of change of the heart signal parameter.  
   
     
     
         19 . A system for detecting a cardiac event in a human patient the system including: 
 (a) at least two sensors configured for obtaining the electrical signal from the patient's heart,    (b) analog-to-digital converter circuitry for digitizing the signal to produce data segments having a time duration that is at least 1 second;    (c) means for processing data segments to identify activity related to each beat, each beat being a sub-segment of the data segment having a measurable R-R interval from the preceding beat;    (d) means for calculating the average R-R interval of the data segment by averaging the R-R intervals of the beats in the data segment;    (e) means to identify short beats within an data segment, a short beat being a beat that has an R-R interval that is a threshold amount less than the average R-R interval of the data segment;    (f) means to detect the cardiac event by processing only the beats in the data segments that are not short beats.    
     
     
         20 . The system of  claim 19  in which the sensors are electrodes adapted for implantation into a body of the patient.  
     
     
         21 . The system of  claim 19  further comprising a housing adapted for implantation into a body, and wherein the housing contains the analog-to-digital converter, the means for processing data segments, the means for calculating the average R-R interval, the means to identify short beats, and the means to detect the cardiac event.  
     
     
         22 . A system for detecting a cardiac event in a human patient the system including: 
 at least two electrodes implanted in the patient for obtaining the electrical signal from the patient's heart, the electrical signal being an electrogram;    an implanted cardiosaver including    (a) analog-to-digital converter circuitry for digitizing the electrogram to produce electrogram segments having a time duration that is at least 1 second;    (b) means for processing an electrogram segment to identify beats of the electrogram, each beat being a sub-segment of the electrogram segment having a measurable cardiac feature;    (c) means for calculating the average of the cardiac feature within electrogram segment by averaging the feature values of the beats in the electrogram segment;    (d) means to identify rejected beats within an electrogram segment, a rejected beat being a beat that has a feature value that is a predetermined amount different than the average of the feature value calculated across an interval;    (e) means to detect the cardiac event by processing only the beats in the electrogram segments that are not rejected beats.    
     
     
         23 . The system of  claim 22  wherein the cardiac feature is the R-R interval, and wherein the identified rejected beats are short beats which have R-R intervals which are less than a selected R-R interval.  
     
     
         24 . A system of  claim 22  wherein the predetermined amount is a function of the average heart rate of the segment.  
     
     
         25 . A system for detecting a cardiac event in a human patient the system including: 
 at least two sensors adapted to obtain an electrical signal from the patient's heart;    a device including: 
 analog-to-digital converter circuitry for digitizing the electrical signal to produce electrogram segments having a time duration of at least 1 second;  
 a processor configured to: 
 identify a plurality of beats within a segment;  
 calculate for each of the plurality of beats a parameter indicative of the interval between each of the plurality of beats and a preceding beat, thereby generating a plurality of heart beat interval values;  
 categorize each of the plurality of beats based on its associated heart beat interval value;  
 detect the cardiac event based at least in part on the categorization of each of the plurality of beats.  
 
   
     
     
         26 . The system of  claim 25  wherein the processor is further configured to calculate a plurality of values of a heart signal parameter for a subset of the plurality of beats that fall into a particular category, and wherein the cardiac event is detected based on the plurality of values of the heart signal parameter.  
     
     
         27 . The system of  claim 26  wherein the heart signal parameter is ST segment shift, and wherein the particular category is those beats that are normal sinus rhythm beats.  
     
     
         28 . The system of  claim 25  wherein the parameter indicative of the interval between each of the plurality of beats and a preceding beat is the R-R interval.