fig1 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 . fig2 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 . fig3 shows in an enlarged scale a portion of the intracardiac iegm signal in fig2 . fig3 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 . fig4 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 fig5 . 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 fig2 – 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 fig1 above . fig6 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 fig6 will replace the procedure that would otherwise occur in autocapture signal processing if no blanking had occurred . the input to the flow chart in fig6 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 fig6 , denotes ventricular blanking . cnt in box 26 in fig6 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 fig6 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 fig7 , 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 fig7 . 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 .
a multi - chamber pacing system has a 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 , including sensing circuits for sensing iegm - signals from each of the heart chambers . each of said sensed iegm signals has a generally known morphology . a signal - reconstructing unit reconstructs the iegm signal from one of the heart chambers in the blanking interval following delivery of a pacing pulse to another heart chamber .