with reference to fig1 - 8 , embodiments of the present invention will now be described . as regards its software aspects , the present invention can be implemented by an appropriate programming of the controlling software of a known implantable medical device , for example , a cardiac pacemaker or a defibrillator / cardioverter , including means for collecting signals provided by endocardial leads and / or one or more implanted or non - implanted sensors . these implantable medical devices include a programmable microcontroller and / or microprocessor circuitry to receive , format , and process electrical signals collected ( detected ) by implanted electrodes and deliver stimulation pulses via pacing electrodes . it is possible to transmit by telemetry software that will be stored in a memory of the implantable medical devices and executed to implement the functions of the present invention . the present invention may particularly be applied to implantable medical devices such as those of the reply , paradym , ovatio , esprit or rhapsody device families produced and marketed by sorin crm , clamart france , formerly known as ela medical , montrouge , france . the adaptation of these implantable medical devices to implement the functions and features of the present invention is believed to be within the abilities of a person of ordinary skill in the art , and therefore will not be described in detail . fig1 illustrates a “ single chamber ” configuration of an implantable medical device in which a generator 10 is associated with a lead 12 implanted in the right ventricle 14 . the lead head has two electrodes , namely a distal electrode 16 and a proximal electrode 18 , which collect a first electrogram v bip corresponding to the potential difference measured between the distal electrode 16 and the proximal electrode 18 , and a second electrogram v uni measured by the potential difference between one of the electrodes , for example , the distal electrode 16 or the proximal electrode 18 , and the metal housing of the generator 10 . in case when the implantable device is a defibrillator , the bipolar signal v bip can also be collected between the distal electrode 16 and a ventricular coil forming a defibrillation electrode 20 , and the unipolar signal v uni can be collected between the metal housing of the generator 10 and the ventricular coil 20 , or between the proximal electrode 18 and the housing 10 when the bipolar signal v bip is collected between the distal electrode 16 and the ventricular coil 20 . it is noted that the present invention is also applicable to the filtering of signals collected in the atrium by an appropriate electrode , or generally to the filtering of any signal collected from an electrode to detect cardiac depolarization signals , particularly multiple signals collected by a multisite device . in general , the term “ cavity ” is used , and can be indifferently applied to an atrium or a ventricle of the right cavities as well as to the left cavities of a patient &# 39 ; s heart . according to embodiment of the present invention , an analysis is performed for each heart beat ( i . e ., a cardiac cycle under analysis ) to distinguish between a valid non - noisy cycle that corresponds to a depolarization wave having a cardiac origin and an invalid noisy cycle that corresponds to an artifact having an extra - cardiac origin , from egm signals that originate from a same cavity , typically the right ventricle , and are collected on two separate channels . fig2 illustrates exemplary egm signals v bip and v uni observed on the ventricular bipolar channel ( fig2 a ) and the ventricular unipolar channel ( fig2 b ) of the configuration as shown in fig1 . it should be understood that it is not necessary to analyze the entire cardiac cycle . rather , the analysis of a significant fraction or a portion of a cardiac cycle ( typically , the portion centered on the qrs complex ) is usually sufficient to discriminate between invalid noisy and valid not noisy cardiac cycles . more specifically , as shown in fig3 , after detecting a depolarization peak on the bipolar signal v bip that corresponds to a detected r wave , the corresponding beat is isolated by a fixed window w of a few tens of milliseconds that is centered on the detected depolarization peak . for example , a suitable window has a width w of 80 ms , corresponding to 80 data points for an algorithm using a sampling frequency of 1 khz . the successive beats b 1 . . . b 8 are simultaneously recorded on the ventricular bipolar channel ( v bip ) and on the ventricular unipolar channel ( v uni ), and the portion of each of these beats contained within the window w is then represented as a characteristic curve in a 2d plane formed by the bipolar channel v bip in abscissa and the unipolar channel v uni in ordinate . this characteristic or feature is referred to as either a “ cardiac loop ” or a “ vectogram ” (“ vgm ”). this vgm represents a complete heart beat in a non - temporal 2d space . as noted above , the vectogram (“ vgm ”) is to be distinguished from a vectocardiogram (“ vcg ”), which is obtained from external ecg electrocardiogram signals , and not from egm signals that are intracardiac cardiac signals . the corresponding vgm v 1 . . . v 8 are shown in fig4 . it is noted that the vgm may not be in a form a closed loop but may represent only a portion of a complete cardiac cycle , including a region of the qrs complex and some leading and following signals isolated inside the window w . it shall be noted that the egm of fig3 and the vgm of fig4 correspond to a sampling frequency of 1 khz , representing about 80 sampling points for each vgm in each analyzed cardiac cycle . the present technique is effective , however , even with a lower sampling frequency , e . g ., 128 hz , giving only about 10 sampling points for a vgm , as in the case of the various cycles used in the analysis algorithms of fig5 and fig6 . the present invention operates , essentially , for each cycle to discriminate between invalid noisy cycles and valid not noisy cycles by analyzing the corresponding vgm . in one embodiment , the analysis is performed as illustrated by the exemplary flowchart of fig5 . the analysis starts with the windowing as explained above in reference to fig3 , by sensing the r wave on the bipolar channel ( step 20 ), searching for the depolarization peak of the r wave ( step 22 ), and selecting a part of the signal that falls within a window of 80 ms centered on or about the peak of the r wave ( step 24 ). at least one descriptor parameter related to the intrinsic morphology of the current vgm is obtained . the analysis of this morphological descriptor parameter determines whether the current cardiac cycle under analysis has a cardiac origin , or is noise . in one embodiment of the present invention , this descriptor parameter is the average angle formed by the consecutive velocity vectors along the path of the vgm , i . e ., the vectors appearing at the data points at which the signal samples are collected based on the sampling rate . the choice of this descriptor parameter is based on the assumption that for a non - noisy cardiac complex ( i . e ., signal whose origin is a cardiac depolarization wave ), two consecutive velocity vectors do not change in direction by too much . indeed , in case of a non - noisy heartbeat , there exists a correlation between the detected signals on both channels that ensures steady vgm progression . conversely , in case of a noisy cycle ( i . e ., an artifact having an extra - cardiac origin ), the vgm progresses erratically , so that two consecutive velocity vectors are directed in different , and sometimes in opposite directions . the choice of the velocity vectors is not limiting , however , and other descriptor parameters can be used — either as an alternative or in complement — to discriminate between cardiac beats and noise . for example , the variance of the average angle between consecutive velocity vectors , or more generally , any descriptor that is representative of a steady progression of the consecutive points of the vgm , may be used . the velocity vector { right arrow over ( v )}( t ) is calculated ( step 26 ) at each point t from a digital filter that approximates the first derivatives v ′ bip ( t ) and v ′ uni ( t ) ( on 4 points for a sampling frequency of 1 khz and on 2 points for a sampling frequency of 128 hz ): v ′ bip ( t )=( v bip ( t + 2 )+ 2 v bip ( t + 1 )− 2 v bip ( t − 1 )− v bip ( t − 2 ))/ 8 v ′ uni ( t )=( v uni ( t + 2 )+ 2 v uni ( t + 1 )− 2 v uni ( t − 1 )− v uni ( t − 2 ))/ 8 { right arrow over ( v )} ( t )=( v ′ bip ( t ), v ′ uni ( t )) to calculate ( step 28 ) the descriptor δv that corresponds to the average angle between two consecutive velocity vectors , one can advantageously use the cosine of each angle . indeed , with unit vectors , the cosine of the angle between two vectors ( a , b ) and ( c , d ) is equal to the scalar product a · c + b · d of these vectors , which greatly simplifies the calculation of the descriptor δv , and is expressed by : δ v =| mean ( cos ( angle ( { right arrow over ( v )} ( 1 ), { right arrow over ( v )} ( 2 ))), cos ( angle ( { right arrow over ( v )} ( 2 ), { right arrow over ( v )} ( 3 ))), . . . , cos ( angle ( { right arrow over ( v )} ( n − 1 ), { right arrow over ( v )} ( n )))− 1 |. the descriptor δv takes values between 0 ( for an angle of 0 °) and 2 ( for an angle of 180 °). according to one embodiment , the descriptor δv hence calculated is compared to a threshold , e . g ., a threshold equal to 0 . 9 ( step 30 ): if δv is greater than the threshold , it is determined that the vgm does not represent a cardiac complex , the cycle is considered as an invalid noisy cycle ( step 32 ), and it is preferably erased from the chain of markers ( step 34 ); if δv is less than or equal to the threshold , the cycle is considered a valid , not noisy cycle , having cardiac beats of a cardiac origin ( step 36 ), and the corresponding marker is validated ( step 38 ). the flowchart in fig6 illustrates a second embodiment of the present invention that is a variant of the first embodiment shown in fig5 . this algorithm avoids or reduces occurrence of under - detection especially in case of ventricular fibrillation . to this end , after calculating the descriptor δv ( steps 20 - 28 , being identical to those same steps 20 - 28 of fig5 ), δv is compared to two different thresholds , one of which depends on the amplitude a of the depolarization peak , stored ( step 40 ) during the search for this peak on the signal of the bipolar channel ( step 22 ). as in the previous case , the descriptor δv is compared to a first threshold threshold 1 independent of the amplitude a of the depolarization peak , but this threshold threshold 1 is set to be greater than the threshold of fig5 , e . g ., 1 . if δv is greater than threshold 1 ( step 42 ), as in the previous case , the cycle is considered an invalid noisy cycle ( steps 32 and 34 ). otherwise , δv is compared to a second threshold threshold 2 , which is less than threshold 1 , for example , threshold 2 = 0 . 8 , and this second threshold is only applied if the amplitude a of the depolarization peak is sufficiently low ( e . g ., amplitude a & lt ; threshold 3 = 3 mv ). if these two conditions are verified , the corresponding cardiac cycle is considered to be an invalid noisy cycle ( steps 32 - 34 ), otherwise , the cycle is considered a valid non - noisy cycle , representative of a cardiac complex ( steps 36 - 38 ). fig7 and fig8 illustrate various examples of vectograms analyzed by the technique of the present invention and respectively classified as noise and valid signals of ventricular fibrillation . the calculated values of the descriptor parameter δv are also indicated in these figures . fig7 illustrates vgms of noisy cycles of non - cardiac origin in which several sharp changes of direction are shown that represent typical noise signals of non - cardiac origin . in contrast , fig8 illustrates vgms of not noisy cycles of cardiac origin in which the transitions are much more gradual for all or almost all sampling points in the vgm . although one or two locally abrupt variations can be seen in fig8 , unlike the noise signals of fig7 , they are still low in count , resulting in a relatively low value for the mean angle , thus reflected in the value of the descriptor δv . various actions are undertaken , preferably as implemented in the controlling software of the implantable medical device , following the classification between valid cycles and invalid cycles , including one or more of the followings : erasing of the markers corresponding to invalid noisy cycles ; possible modification of the sensitivity of the detection circuits ; inhibition of a therapy ; modification of the episodes identification label ; and erasing of the memory of the episodes of noise , especially for non - sustained episodes . if the defibrillator already implements a discrimination algorithm of vt / svt arrhythmias by the technique described in ep 2105843 a1 and its counterpart us patent publication 2010 / 0249626 , the vgm is constituted and analyzed , and velocity vectors are calculated , so that the noise removal technique according to the present invention can be implemented with a very low or no additional cost using the existing software resources . one skilled in the art will appreciate that the present invention can be implemented by other methods and processes than the embodiments disclosed herein , which are provided for purposes of illustration but not of limitation .
apparatus and method for detecting and filtering noise artifacts by analysis of a cardiac vectogram is disclosed . an active medical device collects electrical activity signals of a patient &# 39 ; s heart over a series of cardiac cycles . at least two distinct temporal components are obtained from at least two endocardial electrogram signals that are collected concurrently on different respective channels from the same heart cavity . the means for analyzing and filtering of the active medical device operates by : constructing a non - temporal 2d characteristic of a vectogram of an analyzed cardiac cycle , using a variation of one of the two distinct temporal components as a function of the other ; conducting a morphological analysis of the non - temporal 2d characteristic to derive at least one intrinsic descriptor parameter , including the average angle of velocity vectors of consecutive data points of the 2d characteristic , and classifying the analyzed cardiac cycle as invalid noisy cycle or as valid not noisy cycle , depending on the analysis of the descriptor parameter .