Patent Document

BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a multi-chamber pacing system of the type having pulse generator for successively delivering pacing pulses to chambers of a patient&#39;s heart, and IEGM signal detectors having blanking intervals following the delivery of pacing pulses and including sensing elements for sensing IEGM signals from each of the heart chambers, with each of the sensed IEGM signals having a generally known morphology. 
   2. Description of the Prior Art 
   In the following the term “chambers of the heart” denotes right and left atria as well as right and left ventricles of the heart. 
   U.S. Pat. No. 6,148,234 disclose a dual site pacing system, either bi-ventricular or bi-atrial, wherein signals are sensed during the refractory period following delivery of stimulation pulses. Pacing pulses are delivered substantially concurrently to both the heart chambers, although it is mentioned that for patients with an intra-atrial block the left atrium may be stimulated up to 90 msec later than the right atrium. If capture is achieved in both chambers, no intrinsic depolarization signals can be sensed during the following refractory period. If, however, the threshold of either heart chamber has risen above the level of the delivered pulses, that chamber will not be captured and will not have a refractory period following that delivery of the pulses. In this case, for patients having a conduction delay from one chamber to the other, the excitation signal from the other chamber will be sensed in the non-captured chamber during the refractory period. Such sensing during the pacemaker refractory period is considered to be the result of loss of capture. 
   If two heart chambers are stimulated at somewhat different times, one of the chambers will be blanked when the other one is stimulated. Most pacing systems are constructed such that all signal channels are blanked when a stimulation pulse is emitted. Consequently there will be an interruption in sensed IEGM signals. This occurs in all dual or multi chamber pacing systems, e.g. at both bi-ventricular and bi-atrial pacing. If sensed signals are for instance integrated in an evoked response detection time interval from e.g. 4 msec to 50 msec after stimulation to determine evoked response, and if a stimulation of the other chamber takes place at 10 msec after the first stimulation there will be an interruption of the signal in the aforementioned detection time interval. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide an improved technique for reconstructing the IEGM signal in a reliable way in multi-chamber pacing, e.g. for presenting the IEGM signal in its entirety to a physician or for printing it out. Such a reconstructed signal is also useful for reliable detection of evoked response. 
   The above objects are achieved in accordance with the principles of the present invention in a multi-chamber pacing system of the type initially described, that additionally has a signal reconstructing unit that reconstructs the IEGM signal from one of the heart chambers in the blanking interval following delivery of a pacing pulse to another of the heart chambers. 
   Thus, the basic concept of the present invention is to mathematically reconstruct the IEGM signal sensed in one heart chamber during blanking intervals resulting from stimulation in other chambers. When reconstructing the signal, the knowledge of the general signal morphology is utilized. The pulse generator circuit is controlled to deliver the second pacing pulse with a time delay exceeding the length of the blanking interval following the first one of the two consecutive pacing pulses. It should also be noted that with the present invention it is possible to reconstruct the signal in more than one blanking interval, as may occur in the signal as a result of subsequent stimulations in other chambers of the heart. Such a situation can appear if time delays between the stimulations in different heart chambers are comparatively short. 
   In an embodiment of the pacing system according to the invention the signal-reconstructing unit selects among several predetermined ways of reconstructing the IEGM signal in the blanking interval with the use of the knowledge of the signal morphology. In this way knowledge about the signal morphology is utilized for selecting the best way of reconstructing the signals in the blanking interval. 
   If a constant signal level u 0 , equal to the mean value of the sensed IEGM signal values at the beginning u 1  and at the end u 2  of the blanking interval, is e.g. integrated during the blanking interval inside an evoked response detection time window for evoked response detection, the result may be somewhat noise sensitive, since it depends only the two samples u 1  and u 2 . To reduce this noise sensitivity, another embodiment of the pacing system according to the invention may be used. In this embodiment, a filter is provided to filter the IEGM signal to produce a reconstructed signal. 
   In another embodiment of the pacing system according to the invention, with the pacing system having an implantable lead with a tip and a ring electrode and the pulse generator having a case, IEGM signals are measured between the tip electrode and the case and between the ring electrode and the case, respectively. A memory is provided for storing the IEGM signals, and the signal-reconstructing unit reconstructs the IEGM signal measured between the tip electrode and the case, while using the portion of the stored ring electrode-to-case IEGM signal that corresponds to the blanking interval in the reconstructed IEGM signal for the reconstruction within the blanking interval. Even though the ring electrode may be floating in blood and the tip electrode is attached to the myocardium and the tip and ring electrodes have different shapes, the signals will look quite similar. Since the ring electrode is farther away from myocardium than the tip, the signal resulting from depolarization of myocardium will arrive at the tip electrode before it arrives at the ring electrode. Thus the ring-to-case signal will be delayed compared to the tip-to-case signal. If a tip-to-case signal channel is blanked in a time period, information about this blanking period can be found in the ring-to-case signal after a certain time when none of the two signal channels are blanked. 
   In another advantageous embodiment of the pacing system according to the invention a telemetry arrangement is provided for sending the IEGM signals, including reconstructed signal portions in blanking intervals, to an external programmer for showing IEGMs together with corresponding ECGs on a display and/or printing them out. In this way complete IEGMs, including also blanking intervals, are obtained. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a simplified block diagram of an embodiment of the pacing system according to the invention. 
       FIGS. 2–5  schematically illustrate IEGM signal portions containing a blanking interval for explaining different reconstructing techniques according to the invention. 
       FIG. 6  is a flowchart illustrating an example of evoked response signal processing during blanking in the pacing system according to the invention. 
       FIG. 7  illustrates another embodiment of reconstruction in the pacing system according the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  schematically shows a multi-chamber pacing system with leads  42 ,  44 ,  46  having bipolar electrodes  48 ,  50 ,  52  implanted in right atrium and in the ventricles of a patient&#39;s heart  54 . The pulse generator case is schematically marked at  56 . 
   Inside the pulse generator case there is an IEGM signal detector  58  with IEGM signal sensing circuits and a signal reconstructing unit  60  and a memory means  62 . These components are preferably realized by a microprocessor. 
   IEGM signals are sensed and integrated by the detector  58 . With the signal-reconstructing unit  60  the signal is reconstructed in blanking intervals resulting from delivery of pacing pulses in other heart chambers. In the memory  62  measured complete IEGM signals are stored, such that the reconstructing unit  60  can use the portion of the stored signal that corresponds to the blanking interval. A complete IEGM signal can be measured in advance and stored in the memory  62 . IEGM signals alternatively can be measured simultaneously between tip electrode, e.g. the tip electrode  64  in the right ventricle, and the case  56  and between the ring electrode  66  in the right ventricle, and the case  56 . The measured IEGM signals are stored in the memory  62 . Since the ring-to-case signal is delayed relative to the tip-to-case signal, the signal reconstructing unit  60  reconstructs the IEGM signal measured between the tip electrode  64  and the case  56  while using that portion of the stored ring electrode  66 -to-case  56  IEGM signal that corresponds to the blanking interval in the IEGM signal to be reconstructed. 
     FIG. 2  qualitatively shows the simplified appearance of an IEGM signal as a function of time following the delivery of a stimulation pulse  2 . A blanking interval  4 , resulting from the delivery of a pacing pulse in another heart chamber, is limited by two vertical dashed lines  6 , 8  in the figure. The blanking time is normally 6–15 msec. 
     FIG. 3  shows in an enlarged scale a portion of the intracardiac IEGM signal in  FIG. 2 .  FIG. 3  illustrates an example where the signal during the blanking interval  4  is mathematically reconstructed by using the instant slope at the starting point  10  of the blanking interval. 
     FIG. 4  shows an example with the blanking interval  12  positioned around a minimum  14  in the intracardiac IEGM signal. In this embodiment the signal is reconstructed in the blanking interval by using the instant slopes of the intracardiac signal at the beginning  16  and end  18  of the blanking interval  12  for linear extrapolations of the signal forwardly from the beginning  16  of the blanking interval  12  and rearwardly from the end  18  of the blanking interval respectively. This linear extrapolations meet in an intersection point  20 , thus forming a reconstructed signal in the blanking interval  12 . 
   As another alternative the sensed intracardiac signal can be reconstructed or replaced during blanking by a constant signal level u 0 , e.g. equal to the mean value of the signal values u 1  and u 2  at the ends of the blanking interval  22 , see  FIG. 5 . 
   Instead of linear approximations of the signal within the blanking period as described above the signal can be reconstructed by applying a polynomial of suitable degree to the signal by using a number of IEGM signal samples preceding and succeeding the blanking interval. 
   As can be seen from  FIGS. 2–5  the signal smoothly varies with time without any discontinuities. The general morphology or progress of the signal can be determined in advance by introductory measurements and memorized for the subsequent use, cf. the description of  FIG. 1  above. 
     FIG. 6  is a flow chart illustrating an example of signal processing during blanking in a pacing system according to the invention having an evoked response detector. The evoked response signal processing occurs in e.g. a microprocessor-controlled signal procedure known in the art. The example relates to normal autocapture signal processing just interrupted during blanking caused by stimulation in the heart chamber opposite to the considered chamber. The procedure disclosed in  FIG. 6  will replace the procedure that would otherwise occur in autocapture signal processing if no blanking had occurred. The input to the flow chart in  FIG. 6  is the intracardiac evoked response signal integrated up to the beginning of the blanking interval or blanking point. The flow chart then illustrates the signal processing up to the end of the blanking interval whereafter the integrated evoked response signal is further processed in the normal, well-known way for evoked response detection. 
   VBLNK, see  24  in  FIG. 6 , denotes ventricular blanking. Cnt in box  26  in  FIG. 6  denotes counter value, and U int  denotes integrated ER signal. 
   In box  28  U int  is integrated during VBLNK. The counter value equals the count number of loops, viz. the number of samples during VBLNK. 
   Box  30  illustrates the addition of the integrated value of estimated mean value of the signal during VBLNK to the integrated ER signal U int  up to the beginning of VBLNK. 
   The resulting evoke response signal U evoked response , box  32 , is then further processed, at  34 , for evoked response detection according to well-known technique. 
   Another way of viewing the procedure illustrated in  FIG. 6  is to consider the samples in the ER window as a mathematical vector. By taking the dot product of this vector and the vector for which samples are depicted in  FIG. 7 , U evoked response  is obtained. Given the definition of the product, the value of the integrated linearly interpolated evoked response equals 
             U     evoked   ⁢           ⁢   response       =       ∑     l   =   1     N     ⁢       u   i     ·     f   i               
where u i  are the individual voltage samples in the ER window and f i  the (filter) coefficients depicted in  FIG. 7 .
 
   The value of the filter coefficients immediately preceding and immediately succeeding the blanking period is equal to 1+n/2, where n is the number of samples being blanked. 
   Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.

Technology Category: 1