Abstract:
Methods and systems are disclosed for determining whether a patient is a responder to cardiac resynchronization therapy. The beginning and ending of the intrinsic ventricular depolarization are determined through signals measured from one or more electrodes implanted in the patient&#39;s heart. An interval between the beginning and ending of the intrinsic ventricular depolarization is computed and is compared to a threshold. The threshold may be determined empirically. The pacing parameters of a heart stimulation device, such as a pacemaker, may then be configured, for example, by setting the paced atrio-ventricular delay based on whether the patient responds positively to cardiac resynchronization therapy.

Description:
RELATED APPLICATIONS  
       [0001]    The present application is a continuation-in-part of the application entitled METHOD AND APPARATUS FOR PREDICTING ACUTE RESPONSE TO CARDIAC RESYNCHRONIZATION THERAPY, having U.S. Ser. No. 09/822,790 filed on Mar. 30, 2001 and is also a continuation-in-part of the application entitled METHOD AND APPARATUS FOR DETERMINING THE CORONARY SINUS VEIN BRANCH ACCESSED BY A CORONARY SINUS LEAD, with U.S. Ser. No. 09/822,638 also filed on Mar. 30, 2001. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention is directed to cardiac resynchronization therapy. More specifically, the present invention is directed to methods and systems for detecting whether patients are responders to ventricular resynchronization therapy.  
         BACKGROUND  
         [0003]    The heart is a muscular organ comprising multiple chambers that operate in concert to circulate blood throughout the body&#39;s circulatory system. As shown in FIG. 1, the heart  100  includes a right-side portion or pump  102  and a left-side portion or pump  104 . The right-side portion  102  includes a right atrium  106  and a right ventricle  108 . Similarly, the left-side portion  104  includes a left atrium  110  and a left ventricle  112 . Oxygen-depleted blood returning to the heart  100  from the body collects in the right atrium  106 . When the right atrium  106  fills, the oxygen-depleted blood passes into the right ventricle  108  where it can be pumped to the lungs (not shown) via the pulmonary arteries  117 . Within the lungs, waste products (e.g., carbon dioxide) are removed from the blood and expelled from the body and oxygen is transferred to the blood. Oxygen-rich blood returning to the heart  100  from the lungs via the pulmonary veins (not shown) collects in the left atrium  110 . The circuit between the right-side portion  102 , the lungs, and the left atrium  110  is generally referred to as the pulmonary circulation. When the left atrium  110  fills, the oxygen-rich blood passes into the left ventricle  112  where it can be pumped throughout the entire body. In so doing, the heart  100  is able to supply oxygen to the body and facilitate the removal of waste products from the body.  
           [0004]    To circulate blood throughout the body&#39;s circulatory system as described above, a beating heart performs a cardiac cycle that includes a systolic phase and a diastolic phase. During the systolic phase (e.g., systole), the ventricular muscle cells of the right and left ventricles  108 ,  112  contract to pump blood through the pulmonary circulation and throughout the body, respectively. Conversely, during the diastolic phase (e.g., diastole), the ventricular muscle cells of the right and left ventricles  108 ,  112  relax, during which the right and left atriums  106 ,  110  contract to force blood into the right and left ventricles  108 ,  112 , respectively. Typically, the cardiac cycle occurs at a frequency between  60  and  100  cycles per minute and can vary depending on physical exertion and/or emotional stimuli, such as, pain or anger.  
           [0005]    The contractions of the muscular walls of each chamber of the heart  100  are controlled by a complex conduction system that propagates electrical signals to the heart muscle tissue to effectuate the atrial and ventricular contractions necessary to circulate the blood. As shown in FIG. 2, the complex conduction system includes an atrial node  120  (e.g., the sinoatrial node) and a ventricular node  122  (e.g., the atrioventricular node). The sinoatrial node  120  initiates an electrical impulse that spreads through the muscle tissues of the right and left atriums  106 ,  110  and the atrioventricular node  122 . As a result, the right and left atriums  106 ,  110  contract to pump blood into the right and left ventricles  108 ,  112  as discussed above. At the atrioventricular node  122 , the electrical signal is momentarily delayed before propagating through the right and left ventricles  108 ,  112 . Within the right and left ventricles  108 ,  112 , the conduction system includes right and left bundle branches  126 ,  128  that extend from the atrioventricular node  122  via the Bundle of His  124 . The electrical impulse spreads through the muscle tissues of the right and left ventricles  108 ,  112  via the right and left bundle branches  126 ,  128 , respectively. As a result, the right and left ventricles  108 ,  112  contract to pump blood throughout the body as discussed above.  
           [0006]    Normally, the muscular walls of each chamber of the heart  100  contract synchronously in a precise sequence to efficiently circulate the blood as described above. In particular, both the right and left atriums  106 ,  110  contract (e.g., atrial contractions) and relax synchronously. Shortly after the atrial contractions, both the right and left ventricles  108 ,  112  contract (e.g., ventricular contractions) and relax synchronously. Several disorders or arrhythmias of the heart can prevent the heart from operating normally, such as, blockage of the conduction system, heart disease (e.g., coronary artery disease), abnormal heart valve function, or heart failure.  
           [0007]    Blockage in the conduction system can cause a slight or severe delay in the electrical impulses propagating through the atrioventricular node  122 , causing inadequate ventricular relaxations and filling. In situations where the blockage is in the ventricles (e.g., the right and left bundle branches  126 ,  128 ), the right and/or left ventricles  108 ,  112  can only be excited through slow muscle tissue conduction. As a result, the muscular walls of the affected ventricle ( 108  and/or  112 ) do not contract synchronously (e.g., asynchronous contraction), thereby, reducing the overall effectiveness of the heart  100  to pump oxygen-rich blood throughout the body. For example, asynchronous contraction of the left ventricular muscles can degrade the global contractility (e.g., the pumping power) of the left ventricle  112  which can be measured by the peak ventricular pressure change during systole (denoted as “LV+dp/dt”). A decrease in LV+dp/dt corresponds to a worsened pumping efficiency and less cardiac output.  
           [0008]    Similarly, heart valve disorders (e.g., valve regurgitation or valve stenosis) can interfere with the heart&#39;s  100  ability to pump blood, thereby, reducing stroke volume (i.e., aortic pulse pressure) and/or cardiac output.  
           [0009]    Various medical procedures have been developed to address these and other heart disorders. In particular, cardiac resynchronization therapy (“CRT”) can be used to improve the conduction pattern and sequence of mechanical contractions of the heart. CRT involves the use of an artificial electrical stimulator that is surgically implanted within the patient&#39;s body. Leads from the stimulator can be affixed at a desired location within the heart to effectuate synchronous atrial and/or ventricular contractions. Typically, the location of the leads (e.g., stimulation site) is selected based upon the severity and/or location of the blockage. Electrical stimulation signals can be delivered to resynchronize the heart, thereby, improving cardiac performance.  
           [0010]    Despite these advantages, several shortcomings exist that limit the usefulness of CRT. For example, results from many clinical studies have shown that hemodynamic response to CRT typically varies from patient to patient, ranging from very positive (e.g., improvement) to substantially negative (e.g., deterioration). Thus, in order to predict the benefit from CRT, the patient typically must be screened prior to receiving the therapy. One common method that predicts hemodynamic response to CRT relies on measurement of a surface electrocardiagram (ECG). Such measurement is often performed manually and is subject to human error. Additionally, it is difficult to implement such a surface measurement with an implantable device thereby making it difficult to continuously monitor the response.  
           [0011]    Thus, there is a need for improved methods and systems that can automatically and reliably predict whether a patient will have a positive response to CRT and/or be able to monitor the response continuously during the entire course of CRT.  
         SUMMARY  
         [0012]    Embodiments of the present invention provide methods and systems that detect whether a patient is a responder to CRT. The methods and systems involve making measurements with at least one electrode implanted within the patient&#39;s heart. An implanted heart stimulation device, external device programmer, or other device may then determine from the measurements whether the patient will have a positive response to CRT.  
           [0013]    The present invention may be viewed as a method for determining whether a patient is a responder to resynchronization therapy. The method involves detecting a beginning of an intrinsic ventricular depolarization with an electrode positioned at a ventricle of the heart of the patient. An ending of the intrinsic ventricular depolarization is also detected. An interval between the beginning of the intrinsic ventricular depolarization and the ending of the intrinsic ventricular depolarization is measured. The interval is then compared to a threshold.  
           [0014]    The present invention may also be viewed as a system for determining whether a patient is a responder to resynchronization therapy. The system includes an electrode positioned at a ventricle of the heart of the patient. A detection module is communicatively linked to the electrode, and the detection module detects a beginning of an intrinsic ventricular depolarization and an ending of the intrinsic ventricular depolarization. The system also includes a processing module communicatively linked to the detection module, wherein the processing module computes an interval between the beginning of the intrinsic ventricular depolarization and the ending of the intrinsic ventricular depolarization and compares the interval to a threshold.  
           [0015]    The present invention may also be viewed as another system for determining whether a patient is a responder to resynchronization therapy. The system includes means for detecting a beginning of an intrinsic ventricular depolarization and an ending of the intrinsic ventricular depolarization. Additionally, the system includes means for computing an interval between the beginning of the intrinsic ventricular depolarization and the ending of the intrinsic ventricular depolarization and for comparing the interval to a threshold. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a diagram showing the various chambers of the heart.  
         [0017]    [0017]FIG. 2 is a diagram showing the various chambers and the electrical conduction system of the heart.  
         [0018]    [0018]FIG. 3 is a graph showing ventricular depolarization as a function of time.  
         [0019]    FIGS.  4 - 6  are diagrams illustrating a heart and the electrical conduction system advancing through a normal cardiac cycle.  
         [0020]    [0020]FIG. 7 is a graph illustrating mean percentage change in left ventricular pressure (LV+dp/dt) resulting from application of CRT plotted against the duration of intrinsic ventricular depolarization for responders and non-responders.  
         [0021]    [0021]FIG. 8 is a graph illustrating the accuracy, sensitivity, and specificity of the separation between responders and non-responders for various thresholds of ventricular depolarization duration used to make the distinction.  
         [0022]    [0022]FIG. 9 illustrates one possible embodiment of a system that can be used to detect whether a patient is a responder to CRT.  
         [0023]    [0023]FIG. 10 is an operational flow summarizing the logical operations employed by an exemplary system for detecting whether a patient is a responder to CRT. 
     
    
     DETAILED DESCRIPTION  
       [0024]    Various embodiments of the present invention will be described in detail with reference to the drawings, wherein like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the present invention, which is limited only by the scope of the claims attached hereto.  
         [0025]    The following discussion is intended to provide a brief, general description of a suitable method for predicting whether a patient will positively respond to cardiac resynchronization therapy (“CRT”). As will be described in greater detail below, the method of the present disclosure predicts a patient&#39;s response to CRT by measuring and comparing an intrinsic ventricular depolarization period against a threshold. As will become apparent from the discussion below in connection with the various drawings, the ventricular depolarization period may be measured by finding a beginning and ending of the depolarization through processing of an intracardiac signal to find a beginning value Q* and an ending value S*. However, those of ordinary skill in the art will readily appreciate that the method of the present disclosure can be implemented using any suitable beginning and ending value, which may or may not be found by employing various methods for measuring Q* and S*.  
         [0026]    In a preferred embodiment, the method of the present disclosure predicts whether a patient will respond to CRT by evaluating the period of depolarization of the right or left ventricles  108 ,  112  (FIG. 1). The period of depolarization of the ventricles  108 ,  112  can be evaluated using an intracardiac electrogram. An intracardiac electrogram is generally a graphical depiction of the electrical depolarization or excitement of the heart  100  (FIG. 1) that is measured by one or more electrodes placed on or within the heart  100 , such as within the right or left ventricles.  
         [0027]    An exemplary electrogram for an intrinsic systolic cycle is shown in FIG. 3. Each portion of the electrogram is typically given an alphabetic designation corresponding to a predetermined period of electrical depolarization or excitement. For example, the portion of the electrogram that represents atrial depolarization is commonly referred to as the P-wave (not shown). Similarly, the portion of the electrogram that represents ventricular depolarization is commonly referred to as the QRS complex comprising a Q-wave, an R-wave, and an S-wave. Moreover, the portion of the electrogram that represents ventricular recovery or repolarization is commonly referred to as the T-wave (not shown).  
         [0028]    As shown in FIG. 3, the QRS complex has a beginning and an ending. To determine the beginning and ending, the intracardiac electrogram may be analyzed, as discussed below, to find various representative values. The representative beginning value Q* and ending value S* are shown in FIG. 3. Other values representative of the beginning and ending of the QRS complex may be used in place of the Q* and S* values that are defined by the calculations discussed below.  
         [0029]    Each period of electrical depolarization or excitement represented on the electrogram corresponds to a period of muscular activation within the heart  100  (FIG. 1). FIGS.  4 - 6  are schematic illustrations depicting the various periods of muscular activation within the heart  100 . As shown in FIGS.  4 - 6 , the electrogram data can be monitored using any suitable electrocardiographic device  150 , such as an implantable heart stimulation device (i.e. CRT device), that is connected to leads located on or within the heart  100 .  
         [0030]    [0030]FIG. 4 is a schematic illustration showing the period of atrial activation in response to electrical impulses initiated at the sinoatrial node  120  (corresponding to the P-wave portion as discussed above). After electrical impulses spread from the sinoatrial node  120 , the muscle tissues of the right and left atriums  106 ,  110  contract to pump blood into the right and left ventricles  108 ,  112 , respectively.  
         [0031]    [0031]FIG. 5 is a schematic illustration showing the period of a ventricular depolarization in response to electrical impulses initiated at the atrioventricular node  122  that spread through the ventricles  108 ,  112  (corresponding to the QRS portion as discussed above). After electrical impulses spread from the atrioventricular node  122 , the muscle tissues of the right and left ventricles  108 ,  112  contract to pump blood to the lungs and throughout the body, respectively.  
         [0032]    [0032]FIG. 6 is a schematic illustration showing ventricular recovery or repolarization (corresponding to the T-wave portion as discussed above). During ventricular repolarization, the membrane potential of the muscle cells reverse polarity and return to their resting state, thereby, causing the ventricles to relax.  
         [0033]    An electrogram of a patient&#39;s heart can be used to assess cardiac performance by validating the existence of cardiac abnormalities, such as, arrhythmias evinced by an abnormally fast heart rate (e.g., tachycardia), an abnormally slow heart rate (e.g., bradycardia), or a normal rate but the depolarization is abnormally propagated (e.g., ectopic, or conduction system defect). The existence of an arrhythmia typically indicates that the heart&#39;s rhythm initiation and/or conduction system is functioning abnormally. CRT can be used, among other applications, to treat abnormal electrical conduction. In particular, CRT can be used to deliver electrical stimulation to portions of the heart  100  (FIG. 1) to resynchronize the heart&#39;s activation, thereby, improving the efficiency of atrial and ventricular contractions necessary to circulate blood throughout the body. The amount of benefit derived from CRT, however, typically varies depending upon the severity of the abnormality of the heart&#39;s conduction system. Therefore, prior to treating a patient using CRT, it is preferable to evaluate whether the heart&#39;s  100  (FIG. 1) conduction system is normal or abnormal.  
         [0034]    The heart&#39;s ventricular conduction system can be assessed through analysis of the duration of ventricular depolarization. Identification of patients who may have a positive response to CRT can be performed using the duration of ventricular depolarization (e.g., the width of the QRS complex as shown in FIG. 3) measured from an intracardiac electrogram. For example, if the duration of ventricular depolarization is greater than a given threshold, then the patient may be considered a responder to CRT, and the CRT device for that patient may be configured appropriately. Patients are referred to as responders because they have an abnormal conduction system that can benefit from CRT.  
         [0035]    Once the patient has been deemed a responder or non-responder, the CRT device can be configured to stimulate the heart to produce an atrioventricular delay of a duration appropriate for the patient type as is discussed below. For responders, the atrioventricular delay is generally set to about one-half of the intrinsic, or naturally occurring atrioventricular delay. For non-responders, the atrioventricular delay is set to approximately the intrinsic atrioventricular delay, such as the intrinsic atrioventricular delay minus a relatively small delay factor of about 30 milliseconds. One with ordinary skill in the art will recognize that other atrioventricular delay settings for responders and non-responders are possible as well. The atrioventricular delay is generally considered to be the length of time between an atrial sensed (or stimulated) event and the delivery of a ventricular output pulse.  
         [0036]    [0036]FIG. 7 shows a graph of the mean percent change in peak left ventricle pressure “LV dp/dt” after application of CRT over three atrioventricular delays for a group consisting of both responders and non-responders. Responders may be defined as those who receive an increase in peak left ventricle pressure when CRT is applied. From the graph, one can see that a relationship exists between the intrinsic Q*S* depolarization interval and the increase in peak left ventricle pressure due to CRT. For those having a relatively long intrinsic ventricular depolarization, CRT caused a relatively large increase in peak left ventricle pressure. For those having a relatively short intrinsic ventricular depolarization, CRT caused a relatively small increase or in some instances a decrease in peak left ventricle pressure.  
         [0037]    A linear regression of the test cases shows that the correlation of percent change in peak left ventricle pressure to Q*S* is defined by the equation y=0.3462x −51.807, with a coefficient of determination R 2 =0.3974. The vertical line of FIG. 7 indicates that an appropriate Q*S* threshold for distinguishing responders from non-responders is approximately 175 milliseconds for humans. The determination of 175 milliseconds as an appropriate threshold is further supported by the plot in FIG. 8.  
         [0038]    [0038]FIG. 8 shows the values for the accuracy which represents the probability of correct classification of either a responder or non-responder, sensitivity which represents the probability of correct classification of patients as responders, and specificity which is the probability of correct classification of patients as non-responders plotted against Q*S* thresholds for humans. From this plot, it can be seen that the optimal threshold is about 175 milliseconds for humans because at this point the accuracy and sensitivity are above 0.95 and the specificity is above 0.88.  
         [0039]    One possible embodiment of a CRT system  300  that can be used to implement the methods for determining whether a patient is a responder is illustrated in FIG. 9. As shown in FIG. 9, the CRT system  300  generally comprises a programming device  301  that can be used to regulate stimulation pulses that are delivered to the heart  100 . In one possible embodiment, the heart  100  is connected to various leads  320  having electrodes (not shown) and terminal pins (not shown) that can connect the heart  100  to the CRT system  300 . The various leads  320  connecting the heart  100  to the CRT system  300  will be described in greater detail below.  
         [0040]    The programmer  301  can regulate the stimulation pulses delivered to the heart  100  using, for example, a telemetry module  302 . In one possible embodiment, the telemetry module  302  is unidirectional (e.g., capable of allowing the programmer  301  to receive data). However, in an alternative embodiment, the telemetry module  302  is bi-directional (e.g., capable of allowing the programmer  301  to receive and/or send data). The command input module  304  is configured to interpret the data received from the programmer  301  such that the stimulation pulses can be accurately distributed according to predetermined criteria, such as, the specific requirements of the patient being treated.  
         [0041]    A controller  306  can be used to control the specific instructions regarding the stimulation pulses delivered to the heart  100 . In one possible embodiment, the controller  306  can be controlled manually. In an alternative embodiment, however, the controller  306  can be controlled automatically using, for example, feedback received from an intrinsic signal analyzer  338 . Moreover, one having ordinary skill in the art will readily appreciate that the controller  306  and the programmer  301  can be combined into a single unit. The instructions from the controller  306  are received by an electrode switching and output circuitry module  308  that delivers the stimulation pulses to the appropriate lead  320  within the heart  100 .  
         [0042]    As discussed above, the heart  100  is connected to the CRT system  300  using various leads  320 . The various leads  320  are preferably configured to carry the CRT stimuli from the CRT device to the heart  100 . Moreover, the various leads  320  can likewise operate in a demand mode, thereby, relaying intrinsic cardiac signals from the heart&#39;s  100  electrical conduction system back to one or more sense amplifiers  310 ,  312 ,  314 ,  316 . In one possible embodiment, the various leads  320  comprise separate and distinct leads connecting the CRT system  300  to different portions of the heart  100 . In particular, the various leads  320  can comprise a lead  322  connected to the right-side portion or pump  102  (FIG. 1) of the heart  100 , including, for example, a right atrium lead  324  configured to operate with a right atrium amplifier  310  and a right ventricle lead  326  configured to operate with a right ventricle amplifier  312 . Similarly, the various leads  320  can comprise a lead  327  connected to the left-side portion or pump  104  (FIG. 1) of the heart  100 , including, for example, a first left ventricle lead  328  configured to operate with a first left ventricle amplifier  314  and a second left ventricle lead  330  configured to operate with a second left ventricle amplifier  316 .  
         [0043]    As discussed above, the various leads  320  connected to the heart  100  can relay intrinsic cardiac signals from the heart&#39;s  100  electrical conduction system back to the one or more sense amplifiers  310 ,  312 ,  314 ,  316 . The intrinsic cardiac signals amplified by the sense amplifiers  310 ,  312 ,  314 ,  316  can then be processed by an intrinsic signal analyzer  338  incorporated in whole or in part by an implantable heart stimulation device (i.e., CRT device) or a device programmer. The intrinsic signal analyzer  338  generally can comprise a detection module  340  that is configured to analyze the intracardiac electrogram information to detect the beginning and ending of ventricular depolarization, such as the Q* and S* values discussed above with reference to FIG. 3.  
         [0044]    Calculating Q* and S* from the intracardiac electrogram signal may be done in various ways. See for example, the calculation of Q* from U.S. Pat. No. 6,144,880, which is commonly assigned to Cardiac Pacemakers, Inc. and is incorporated herein by reference. In one embodiment, calculating Q* and S* may proceed as follows. For Q*, a waveform V(n) including the QRS complex must be acquired and analyzed, such as by the detection module  340  of the CRT device or CRT device programmer. The acquisition involves digitizing the waveform V(n) including the activity beginning at the time of an atrial reference marker indicating the end of atrial activity and extending beyond the QRS complex received by the electrode in the left or right ventricle and storing it in memory of the CRT device or CRT device programmer. Then, Q* is found by the following process.  
         [0045]    First, the detection module  340  smooths the waveform V(n). This may be done by smoothing the waveform V(n) seven times using a 5 point rectangular moving window (for a sampling frequency of 500 Hz) whereby the 5 samples for each window are averaged and the average is assigned to the middle sample of the five. A derivative dV(n)/dt of the smoothed waveform is taken, and the absolute value of the derivative dV(n)/dt is normalized to range from 0 to 1.  
         [0046]    The time samples n from the atrial reference marker time T p  to the time T R  of the peak of the R wave of the QRS complex are analyzed. This analysis involves calculating the mean and standard deviation of both the smoothed waveform V(n) and the normalized absolute value of its derivative dV(n)/dt for each time sample within a 50 ms moving window. The baseline window with the minimum mean (i.e., baseline mean) plus a baseline standard deviation for |dv(n)/dt| is found and its values are used in the following steps.  
         [0047]    For each sample n between T p  and T R  if the baseline mean is less than |dV(n)/dt|, but more than or equal to |dV(n)/dt|, then the number of data points N in another 50 ms window is found. N is the accumulation of each data point /nw where |dv(nw)/dt| is greater than the baseline mean plus the baseline standard deviation. The window sample nw of this other window ranges from n to n plus the total number of data points in the window.  
         [0048]    If N divided by the total number of data points in the window is greater than 0.96 and T q =0, then set T q  equal to n0−1, where T q  is the current result of sample time for Q* and n0 is the time sample of the first data point that contributes to N. If the total number of data points in the window minus N is greater than or equal to 2, then T q  is reset to zero. After this is completed for all values of n between T p  and T R , then the final value of T q  is used as Q*. This process may be repeated to obtain a value of Q* for several beats, such as 16, and the median of these Q* values may be used in the computation of the ventricular depolarization interval. It may be desirable to include Q* values in the median determination for beats where the interval from R wave peak to R wave peak between beats has a variation within 10%.  
         [0049]    For S*, the same process may be repeated but the time samples n ranging from the time T p +1 which occurs after sensing atrial activity in the next cycle until the time T R  of the peak of the R wave of the QRS complex of the current cycle are analyzed rather than the samples occurring prior to the R wave peak. Once the process discussed above has been completed for all values starting at T p +1 and continuing to T R  (i.e., working backwards through the samples with respect to time), the final value of T q  is used as S*. As with Q*, this process for S* may be repeated to obtain a value of S* for several beats, such as 16, and the median of these S* values may be used in the computation of the ventricular depolarization interval.  
         [0050]    After analysis of the electrogram information to find the beginning and ending of ventricular depolarization such as Q* and S*, a processing module  342  may compute the duration of depolarization and compare it to a threshold value, such as 175 milliseconds, in accordance with the method described below with reference to FIG. 10 to validate the patient as a responder or non-responder. A configuration module  344  can be used to make adjustments to the CRT system  300  based upon whether the processing module  342  determines the patient to be a responder or non-responder. The adjustments may include setting the atrioventricular delay of the CRT device to about one-half of the intrinsic value for responders or to approximately the intrinsic value for non-responders. For embodiments where the device programmer includes all or part of the intrinsic signal analyzer  338 , the device programmer may send an instruction through telemetry  302  to the implanted heart stimulation device to set the atrioventricular delay.  
         [0051]    The method of the present disclosure can be implemented using a CRT system as shown in FIG. 9 comprising various devices and/or programmers, including implantable or external CRT devices and/or programmers such as a CRT tachy or brady system. Accordingly, the method of the present disclosure can be implemented as logical operations controlling a suitable CRT device and/or programmer. The logical operations of the present disclosure can be implemented: (1) as a sequence of computer implemented steps running on the CRT device and/or programmer; and (2) as interconnected machine modules within the CRT device and/or programmer.  
         [0052]    The implementation is a matter of choice dependant on the performance requirements of the CRT device and/or programmer implementing the method of the present disclosure and the components selected by or utilized by the users of the method. Accordingly, the logical operations making up the embodiments of the method of the present disclosure described herein can be referred to variously as operations, steps, or modules. It will be recognized by one of ordinary skill in the art that the operations, steps, and modules may be implemented in software, in firmware, in special purpose digital logic, analog circuits, and any combination thereof without deviating from the spirit and scope of the present invention as recited within the claims attached hereto.  
         [0053]    [0053]FIG. 10 shows an exemplary embodiment  346  of the logical operations of the processing module  342 . The process begins by the processing module  342  receiving the Q* and S* values from the signals measured by detection module  340  at receive operation  348 . At interval operation  350 , the processing module  342  computes the time interval between the Q* and S* values. At query operation  352 , the processing module  342  compares the Q*S* interval to the threshold, such as 175 milliseconds.  
         [0054]    If the processing module  342  determines that Q*S* is greater than the threshold, then the processing module  342  selects an atrioventricular delay that is about one-half of the intrinsic atrioventricular delay at delay operation  354 . If the processing module  342  determines that Q*S* is less than or equal to the threshold, then the processing module  342  selects an atrioventricular delay that is approximately equal to the intrinsic atrioventricular delay at delay operation  356 . It is desirable at delay operation  356  to set the atrioventricular delay to the intrinsic atrioventricular delay value less a small delay factor of about  30  milliseconds. The configuration module  344  then implements the atrioventricular delay selected by processing module  342  when applying CRT or other pacing therapy to the patient.  
         [0055]    While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various other changes in the form and details may be made therein without departing from the spirit and scope of the invention.