Abstract:
A method utilizing computer processing for detecting, within a cardiac cycle, the earliest onset of global, Q-onset, ventricular depolarization in the presence of an operating pacemaker. The method, in general terms, features (a) gathering a plurality of ECG-obtained QRS heart-cycles waveforms, (b) identifying and categorizing of evidences and specific timings therein of intrinsic Q-onset and pacemaker spike events, (c) looking in a single, selected QRS waveform, between specific, defined first and second time marks, for the most significant slope change appearing in that waveform, and (d) designating to be the correct Q-onset that event which immediately precedes that slope change.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to the filing date, Oct. 26, 2007, of U.S. Provisional Patent Application Ser. No. 61/000,615, covering an invention entitled “Q-Onset Ventricular Depolarization Detection in the Presence of a Pacemaker”. The entire disclosure content of that prior-filed provisional application is hereby incorporated herein by reference. 
     
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
       [0002]    In electrocardiography, the so-called QRS-onset, or Q-onset, in each cardiac-beat, or cardiac cycle, marks the start of electrical depolarization of the heart ventricles. In the context of correlated electroacoustic cardiography, this well-recognized QRS-onset (or Q-onset, a term which is used herein interchangeably with QRS-onset) fiducial is important as a reference for computing the respective durations of a number of important heart-functionality time intervals, such as the electromechanical activation time interval (EMAT) between Q-onset and the closure of the mitral valve. In fact, and as those skilled in the art well know, one of the most important measurements which is relied upon in terms of assessing a person&#39;s heart functionality is this EMAT time interval, also referred to as the QS 1  time interval—the time interval between Q-onset and the occurrence of the first heart sound (S 1 ). Accordingly, accurate determination of the time of Q-onset in each cardiac cycle is extremely critical to heart-behavior assessment. 
         [0003]    In circumstances where a pacemaker is in place in a subject, Q-onset presence and timing confusion can occur. For example, if a particular cardiac cycle is in fact initiated by a ventricular pacemaker impulse, referred to as a pacer spike, rather than by an intrinsic (anatomical) Q-onset event, then the onset of depolarization is best represented by the occurrence time of such a pacer spike. Knowing what is the truth about the time-initiation of depolarization onset is, of course, mandatory for achieving measurement accuracy based upon this initiation event, and so it is very important to distinguish these two different kinds of depolarization-initiation events so as to identify clearly what event to select as the one representing true Q-onset. Put another way, and as those skilled in the art well recognize, where a pacemaker is present, one cannot simply rely on pacemaker-activity output to describe, with confident accuracy, the reality of Q-onset, because of the fact that the relevant pacemaker (a) may be out of synchronization, (b) may possibly be an atrial rather than a ventricular pacemaker, and (c) if it is a bi-ventricular pacemaker, there must be some way of identifying which heart chamber is specifically associated with pacemaker activity. 
         [0004]    In this setting, accordingly, the present invention is concerned particularly with identifying, with as much accuracy as possible, the time, during each heartbeat, of true Q-onset. In a more particular sense, the present invention is concerned with clearly identifying this Q-onset event in a circumstance where a subject is equipped with a pacemaker whose pacing pulses may (but not necessarily so) be the true indicators of Q-onset. 
         [0005]    In relation to the preferred and best-mode manner of practicing the present invention, which includes algorithmically programmed computer processing, there are several categories of ECG and pacemaker information which are especially relevant. These categories define the key pieces of input information which, for a selected, predetermined time span (such as about 10-seconds), which includes a number—a collection—of successive cardiac cycles, are gathered/obtained and supplied to what is referred to herein as a Q-Onset Selection block which, essentially, takes the form of at least a portion of an appropriately algorithmically programmed digital computer that forms one of the central operational systemic “components” of the invention. It is by the operation of this block that an accurate assessment of Q-onset is made. 
         [0006]    Such input information supplied to this block preferably includes conventional, multi-lead (such as 12-lead, though a lesser number of leads may be employed if desired) ECG information which also carries accompanying information defining, for each cardiac cycle in the collection of the mentioned number of gathered, successive cardiac cycles, the time locations of conventionally detected (intrinsic) Q-onset events and of pacemaker spike events. Another piece of input information is derived directly from a selected, single ECG lead, such as the so-called V-4 ECG lead. Also supplied to the Q-Onset Selection block is information specifically relevant to pacemaker, or pacer, operation, derived synchronously from the just-mentioned, conventionally acquired ECG information. This pacemaker-operation information specifically includes pacer spike information in terms of the time occurrences of pacer spikes, as well as their types, i.e., as being either atrial, ventricular, first bi-ventricular, or second bi-ventricular, and more broadly speaking as being either ventricular or bi-ventricular. 
         [0007]    Still a further piece of information which is relevant, and which may be supplied by the same equipment and methodology which supplies the mentioned, conventionally acquired ECG information, is a characterization of the types of heartbeats, or cardiac cycles, which have been detected during the above-mentioned, predetermined time span. In this regard, there are recognized, for the purpose of the description of the present invention, to be two, different, so-called cardiac cycle types, one of which is referred to as being an intrinsically, or internally (i.e., by the anatomy), initiated cardiac cycle, and the other of which is referred to as being a pacer-spike-initiated cardiac cycle. 
         [0008]    With such input information, the Q-onset selection activity of the invention functions to produce, among other things as reportable output information, the relevant, confirmation, Q-onset timing and identity output information. This output information fundamentally, and variously, defines, for each cardiac cycle involved in an investigation, (a) the times within these cycles of “best-determined” Q-onset, (b) the identifying class (per cycle) of the associated, selected, Q-onset event as being either an intrinsic event or a pacer event, and (c) the associated cycle class-identity (intrinsic or pacer). 
         [0009]    In general terms, such Q-onset selection, per cardiac cycle, uniquely involves (1) during a predetermined time span which includes a plurality of successive, QRS cardiac cycles, gathering both ECG and pacemaker-spike information for, and within, each such cycle, (2) with respect to each such gathered cardiac cycle, time-locating, identifying and time-position sorting, first to last, each intrinsic Q-onset and each pacemaker-spike event, including specifically identifying each pacemaker-spike event as being one of ventricular or bi-ventricular, (3) also with regard to each such cardiac cycle, evaluating, with respect a single, selected, QRS waveform, the waveform slope therein from (a) a time just preceding, to (b) a time just following, the mentioned, time-position sorted, first-in-time and last-in-time one of such time-located, identified and sorted events, respectively, (4) from the mentioned slope evaluating practice, finding the time, in the mentioned, single, selected QRS-waveform, of the first substantial QRS-waveform slope change, (5) in each cardiac cycle, selecting to be the correct Q-onset therein the time-sorted event in that cycle whose time position most immediately precedes the time of the mentioned, found, first-substantial slope change, and (6) with respect to each cardiac cycle, maintaining the identity of the selected to-be-correct Q-onset event. 
         [0010]    Such Q-onset determination is followed, among other things, by appropriate presenting and/or reporting of the determination outcome so as to enable thereafter, and as an illustration of special utility, accurate calculation of the kinds of important heart-functionality time intervals, like the EMAT interval mentioned earlier herein. 
         [0011]    These and other features, advantages and reportable Q-onset outcomes which are offered by the present invention will become more fully apparent as the detailed description of the invention which follows below is read in conjunction with the accompanying drawings. This detailed invention description is specifically presented in block/schematic structural and methodologic drawings, and in text terminology, both very familiar to those generally skilled in the relevant art. Accordingly, unnecessary details that define medical terminology are not included herein. Also not specifically included are lines/details of computer-programming code which may conventionally be employed by ones skilled in the programming art to implement the two algorithms which are set forth herein in very understandable, high-level, algorithmic terminology and architecture. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a high-level, block/schematic diagram generally illustrating the preferred and best-mode embodiment of, and the manner of practicing, the methodology of the present invention. 
           [0013]      FIG. 2  is a more elaborated, block/schematic diagram illustrating in somewhat greater detail that which is pictured more generally in  FIG. 1 .  FIG. 2  specifically shows practice of the invention employing a pacemaker (pacer) spike detector and a pacemaker (pacer) spike classifier for providing pacemaker spike information relevant to Q-onset detection and identification. 
           [0014]      FIG. 3  is a fragmentary, block/schematic diagram describing one modified form of the invention. This figure shows practice of the invention wherein pacemaker information is supplied by a conventional pacemaker (pacer) programmer device. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    Turning now to the drawings, and referring first of all to  FIG. 1 , here, illustrated generally at  10 , and including four, “high-level” blocks  12  (Input ECG Information),  14  (Input Pacer Spike Information),  16  (Q-Onset Selection),  18  (Output) is a broad, overview illustration of the preferred and best-mode embodiment of, and manner of practicing, the present invention. A lateral bracket  20  in this figure represents the presence and utilization of a suitably programmed digital computer which performs all required data processing in the practice of the invention. More will be said about this computer, and its operation, shortly. 
         [0016]    Block  12  represents the action of conventional ECG-lead collection, and thereafter the inputting from block  12  to block  16 , via a data-flow connection  12   a,  of the several kinds of relevant ECG information mentioned above herein, as well as certain, relevant pacemaker (pacer) spike information which is naturally acquired over the employed ECG leads. Block  14  represents the gathering from block  12 , over a data-flow connection  12   b,  and the inputting, via a data-flow connection  14   a  also to block  16 , of similar, relevant pacemaker spike information, as generally mentioned earlier herein, derived from block  12 . To the extent that data processing is, or may be, required in the handling of the flow of information within, and from, blocks  12 ,  14 , computer  20  takes care of these tasks. 
         [0017]    Information provided over connections  12   a,    14   a  by blocks  12 ,  14 , respectively, to block  16 , wherein Q-Onset Selection takes place in accordance with practice of the present invention, is appropriately computer processed by computer  20  within the environment of block  16  utilizing a unique algorithm identified herein (and described architecturally in instructive detail below) as Algorithm I. Such information processing within block  16  results, as will shortly be explained, and through a block  16  to block  18  data-flow connection  16   a,  in the supply, to and via Output block  18 , of accurately determined Q-onset timing information, as well as Q-onset type classification/identification, and certain other pieces of important information for, and in relation to, each of the earlier mentioned, selected-time-span number of successive cardiac cycles. In this regard, it should be understood that the illustrative selection of ten-seconds for a useful, predetermined time span is not a required, or “magic”, time-span number. Any appropriate, predetermined time span may be chosen, though ten-seconds for such a span has proven to be entirely satisfactory. 
         [0018]    From the computer-processed information presented as output information by Output block  18 , accurate Q-onset, and certain other, valuable information is made available for all subsequent purposes, such as for calculating the time durations of various important heart-functionality parameters, like the previously mentioned EMAT parameter. 
         [0019]    Turning attention now to  FIG. 2 , as can be seen, several of the blocks which appear in this figure are the same as several, like blocks which appear in just-described  FIG. 1 . More specifically, previously mentioned blocks  12 ,  16 ,  18  appear in  FIG. 2 , along with two additional blocks  22 ,  24 . Also appearing similarly in  FIG. 2  is lateral bracket  20  representing the previously mentioned, algorithmically programmed digital computer which furnishes all data processing required in accordance with practice of the invention. 
         [0020]    Block  22  takes the form of a conventional pacer spike detector. Block  24  takes the form of a unique, computer- 20 -implemented pacer spike classifier which is constructed, and which performs, in accordance with a unique algorithm, described below as Algorithm II, created and operational in accordance with features of the present invention. Blocks  22 ,  24  collectively function as previously mentioned block  14  which appears in  FIG. 1 . 
         [0021]    As will be mentioned further, computer  20  implements Algorithms I and II, and the operations and behaviors of blocks  16 ,  24 , respectively, will shortly be described in the contexts of these two algorithms. 
         [0022]    Completing a description of what is shown specifically in  FIG. 2 , several additional data-flow connections are shown variously interconnecting the several blocks pictured in this figure. In particular, a data-flow connection  26  carrying multiple-lead ECG information connects block  12  to the pacer spike detector. A data-flow connection  28 , carrying the same ECG information, connects block  12  with the pacer spike classifier. Connections  26 ,  28  collectively make up previously described data-flow connection  12   b.  A data-flow connection  30  supplies information from the pacer spike detector to the pacer spike classifier. 
         [0023]    From block  12 , a data-flow connection  32  provides Q-Onset Selection block  16  with multi-lead ECG information, and a data-flow connection  34  supplies, from block  12  to Q-Onset Selection block  16 , single-ECG-lead V4 ECG information. The information supplied over connection  32  includes, for each of the previously mentioned, successive cardiac cycles, the perceived times of intrinsic Q-onset and pacer spike events present during those cycles. Connections  32 ,  34  collectively make up previously mentioned data-flow connection  12   a.    
         [0024]    Extending from the pacer spike classifier  24  is a data-flow connection  36  which is the same as previously described data-flow connection  14   a,  and which supplies, from the classifier to Q-Onset Selection block  16 , pacer spike times and classifications detected and processed by blocks  22 ,  24  during the predetermined time span of cardiac-cycle gathering. As was mentioned earlier, the manner of operation of classifier  24  in accordance with Algorithm II will be explained shortly. 
         [0025]    Within the control of block  16 , in cooperation with blocks  12 ,  22  and  24 , under the operation of digital computer  20 , and under circumstances wherein information, as generally described above, is supplied to block  16  via connections  32 ,  34 ,  36 , which information has been gathered and processed by blocks  12 ,  22 ,  24  over the period of time embracing the above-mentioned gathering of successive cardiac cycles, Q-onset determination/selection is performed in accordance with the following Algorithm I. 
       Algorithm I 
       [0000]    
       
         
           
             1. With respect to each gathered cardiac cycle, time-locate, identify and time-position sort, first to last, each intrinsic Q-onset, and each pacemaker-spike, event, including specifically identifying each pacemaker-spike event as being one of ventricular or bi-ventricular; 
             2. Also with regard to each such cardiac cycle, evaluate, with respect a single, selected, QRS waveform, the waveform slope therein from (a) a time just preceding, to (b) a time just following, the mentioned, time-position sorted, first-in-time and last-in-time one of such time-located, identified and sorted events, respectively; 
             3. Based on such slope evaluating, find the time, in the mentioned, single, selected QRS-waveform, of the first substantial QRS-waveform slope change; 
             4. In each cardiac cycle, select to be the correct Q-onset therein the time-sorted event in that cycle whose time position most immediately precedes the time of the mentioned, found, first-substantial slope change, and 
             5. With respect to each cardiac cycle, maintain the identity of the selected-to-be-correct Q-onset event. 
           
         
       
     
         [0031]    In the preferred implementation of Algorithm I by computer- 20  processing, slope evaluating is performed by the computer effectively using a line having a length of about 14-milliseconds in duration as a projection on the QRS-waveform time axis of the subject, single, selected QRS-waveform wherein slope is being evaluated, (a) with both ends of this line lying on that waveform, (b) by moving the line from a first time which is just before the above-mentioned, first-in-time, time-sorted event, to a second time, which is just after the above-mentioned, last-in-time, time-sorted event, and (c) by noting the magnitude of the slope in existence at points distributed on the subject waveform between these just-stated first and second times. In this slope-evaluating practice, the single, selected waveform employed for this purpose is that which comes from the V4 ECG lead via connection  34 . 
         [0032]    In the invention practice illustrated in  FIG. 2 , pacer spike information delivered to block  16  over connection  36  from the pacer spike classifier is developed in the classifier in accordance with the implementation by computer  20  of what has been referred to above as being Algorithm II. 
         [0033]    The steps of this algorithm, expressed in terms well understood by those skilled in the relevant art, and performed in relation to the totality of the successive cardiac cycles gathered during the predetermined time span, are as follows. 
       Algorithm II 
       [0000]    
       
         
           
             1. Compute the “forward difference” time intervals between each pacer spike in the preceding, two pacer spikes; 
             2. Compute the “backward difference” time intervals between each pacer spike and the subsequent, two pacer spikes; 
             3. Associate each pacer spike with the cycle having the most proximal QRS-onset time; 
             4. Compute the “Q. difference” as the time interval between each pacer-spike time and the QRS-onset time of the associated cycle; 
             5. For each pacer spike time, compute three similarity scores against each of the other pacer times as 
             (a) the absolute difference between the forward differences, 
             (b) the absolute difference between the backward differences, and 
             (c) the absolute difference between the Q. difference; 
             6. Combine the three similarity scores as appropriate, taking into account the validity of each; 
             7. Group with each pacer spike all other pacer spikes having a similarity score below a predetermined threshold; 
             8. Allow only one pacer spike per cycle to be in each pacer-spike group, discarding duplicates; 
             9. Allow only three pacers spikes to be associated with each cycle; 
             10. For each cycle, assign each pacer spike to the appropriate type (atrial, ventricular, bi ventricular) based on its timing relative to QRS-onset and the presence of other pacers spikes in that cycle; 
             11. Ensure that all pacer spikes in a group have the same type by looking across all cycles; 
             12. Check for consistency of timing relative to QRS-onset of pacer spikes of the same type; 
             13. Require biventricular pacer spikes to come in pairs, discarding the ones that are not paired; and 
             14. Report the times, types, and cycle associations of the valid pacer spikes. 
           
         
       
     
         [0051]    Following implementation of both algorithms in the full practice of the invention, output information is reported/presented, etc., by block  18 . This output information preferably includes, for each cardiac cycle involved in a plural-cycle investigation seeking Q-onset as described above, (a) the times within the plural cycles of “best-determined” Q-onset, (b) the identifying class (per cycle) of the associated, selected, Q-onset event as being either an intrinsic event or a pacer event, and (c) the associated cycle class-identity (intrinsic or pacer). The output information made available by practice of the invention is highly accurate in terms of the key task of reliably identifying “real” Q-onset notwithstanding the possible confusing presence of a pacemaker, and therefore sets the stage for reliable and accurate determinations of various, Q-onset-dependent, heart-functionality time-duration parameters, such as the earlier-mentioned, important EMAT parameter. 
         [0052]    Focusing attention now on the fragmentary illustration presented in  FIG. 3 , here the structure and methodology  10  of the present invention are illustrated in a modified form. Pacer spike “detection” and classification information is supplied to block  16  via connection  36  from a conventional pacer programmer which is represented by a block  38  in this figure. Except for the fact that here this pacer spike detection and classification information is supplied differently from the manner in which it is supplied in accordance with the illustration seen in  FIG. 2 , in all other respects, the operation of the methodology of the invention is identical, in terms of computer- 20  implementation of Algorithms I, II to the gathered and processed ECG and pacer spike data. 
         [0053]    Accordingly, a unique and highly accurate methodology for determining Q-onset in the presence of an operating pacemaker has been illustrated and described herein, in preferred and best-mode, and in modified, forms. And, while this is so, we recognize that a number of variations and modifications may be perceived and implemented by those generally skilled in the relevant art without departing from the scope and spirit of the invention.