Apparatus and method for optimizing atrioventricular delay

Systems and methods to optimize atrioventricular delay during sensing or pacing of the atrium and for a plurality of sensed rates or pacing rates. In one example, a paced atrioventricular delay is calculated using a sensed atrioventricular interval and a paced atrioventricular interval. In another example, a plurality of paced atrioventricular delays for different pacing rates can be calculated. In another example embodiment, a plurality of sensed atrioventricular delays for different sensing rates can be calculated. Combinations of the various systems and methods are also possible.

TECHNICAL FIELD

The present invention is directed to cardiac resynchronization therapy systems. More specifically, the present invention is directed to systems and methods to optimize atrioventricular delay during cardiac resynchronization therapy.

BACKGROUND

The heart is a muscular organ comprising multiple chambers that operate in concert to circulate blood throughout the body's circulatory system. As shown inFIG. 1, the heart100includes a right-side portion or pump102and a left-side portion or pump104. The right-side portion102includes a right atrium106and a right ventricle108. Similarly, the left-side portion104includes a left atrium110and a left ventricle112separated by an interventricular septum105. Oxygen-depleted blood returning to the heart100from the body collects in the right atrium106. When the right atrium106fills, the oxygen-depleted blood passes into the right ventricle108where it can be pumped to the lungs (not shown”) via the pulmonary arteries117.

Within the lungs, waste products such as 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 heart100from the lungs via the pulmonary veins (not shown) collects in the left atrium110. The circuit between the right-side portion102, the lungs, and the left atrium110is generally referred to as the pulmonary circulation. After the left atrium110fills, the oxygen-rich blood passes into the left ventricle112where it can be pumped throughout the entire body. In so doing, the heart100is able to supply oxygen to the body and facilitate the removal of waste products from the body.

To circulate blood throughout the body'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, or systole, the ventricular muscle cells of the right and left ventricles108and112contract to pump blood through the pulmonary circulation and throughout the body, respectively. Conversely, during the diastolic phase, or diastole, the ventricular muscle cells of the right and left ventricles108and112relax, during which the right and left atriums106and110contract to force blood into the right and left ventricles108and112, 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.

The contractions of the muscular walls of each chamber of the heart100are 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 inFIG. 2, the complex conduction system includes an atrial node120(the sinoatrial node) and a ventricular node122(the atrioventricular node). The sinoatrial node120initiates an electrical impulse that spreads through the muscle tissues of the right and left atriums106and110and the atrioventricular node122. As a result, the right and left atriums106and110contract to pump blood into the right and left ventricles108and112, as discussed above.

At the atrioventricular node122, the electrical signal is momentarily delayed before propagating through the right and left ventricles108and112. Within the right and left ventricles108and112, the conduction system includes right and left bundle branches126and128that extend from the atrioventricular node122via the Bundle of His124. The electrical impulse spreads through the muscle tissues of the right and left ventricles108and112via the right and left bundle branches126and128, respectively. As a result, the right and left ventricles108,112contract to pump blood throughout the body as discussed above.

Normally, the muscular walls of each chamber of the heart100contract synchronously in a precise sequence to efficiently circulate the blood as described above. In particular, both the right and left atriums106and110contract and relax synchronously. Shortly after the atrial contractions, both the right and left ventricles108and112contract 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.

Blockage in the conduction system can cause a slight or severe delay in the electrical impulses propagating through the atrioventricular node122, causing inadequate ventricular contraction, relaxation, and filling. In situations where the blockage is in the ventricles (e.g., the right and left bundle branches126and128), the right and/or left ventricles108and112can only be excited through slow muscle tissue conduction. As a result, the muscular walls of the affected ventricle (108and/or112) do not contract synchronously (known as asynchronous contraction), thereby reducing the overall effectiveness of the heart100to pump oxygen-rich blood throughout the body.

Various medical procedures have been developed to address heart disorders. In particular, cardiac resynchronization therapy (“CRT”) can be used to improve the conduction pattern and sequence of the heart100. CRT involves the use of an artificial electrical stimulator that is surgically implanted within the patient's body. Leads from the stimulator can be affixed at a desired location within the heart100to effectuate synchronous atrial and/or ventricular contractions. Typically, the location of the leads, or the 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.

One important parameter associated with CRT is atrioventricular delay or “AV delay,” which is the programmed time interval between a paced or sensed atrial event and the corresponding paced or sensed ventricular event. Referring toFIGS. 3-7, an example timeline and method are shown for calculating an AV delay.

Referring toFIG. 3, a specific instant in atrial (“A”) and ventricle (“V”) activity is illustrated. For example, the sensing of atrial (“As”) activity and sensing of ventricle (“Vs”) activity during intrinsic heart activity is shown for a single heartbeat. The time Asrepresents when atrial depolarization (or electrical activation) is sensed. The time Vsrepresents when ventricular depolarization is sensed. The interval between Asand Vsis the sensed atrioventricular interval (“AVIs”).

The AVIscan be used to calculate an optimal AV delay for ventricular pacing during intrinsic or sensed atrial contraction (“AVDs”), as shown inFIG. 4, using various techniques. For example, methods described in U.S. Pat. No. 6,144,880 to Ding et al. and U.S. patent application Ser. Nos. 10/314,899 and 10/314,910 to Yu et al., all of which are hereby incorporated by reference in their entireties, can be used to calculate AVDsfrom AVIs. Equation 1 below generally illustrates one possible relationship between AVIsand an optimized AVDs.
AVDs=K1(AVIs)−K2   (1)
The constants K1and K2may vary depending on the interval measured and patient diversity. See U.S. Pat. No. 6,144,880.

In another example, U.S. patent application Ser. No. 10/352,780 to Ding et al., which is hereby incorporate by reference, describes methods for calculating optimal AVDS. For example, the following equation can be used to calculate an optimal AVDs: AVDs=k1AVRs+k2AVLs, where AVRsis the interval between atrial sense and right ventricular sense, and AVLsis the interval between atrial sense and left ventricular sense.

Referring now toFIG. 5, an embodiment in which the atrium is paced (“Ap”) is illustrated. Aprepresents the introduction of an electrical impulse to the atrium, and, as previously noted, Vsrepresents sensing of intrinsic ventricular activity. The interval between Apand Vsis the atrioventricular interval during atrial pacing and ventricular sensing (“AVIp”).

As shown inFIG. 6, a difference between AVIsand AVIp, labeled as the offset, can be calculated using Equation 2.
offset=AVIp−AVIs(2)
Using this offset, the optimal atrioventricular delay for atrial and ventricular pacing (“AVDp”) can be calculated using Equation 3.
AVDp=AVDs+offset  (3)

Referring now toFIG. 7, using Equations 2 and 3 described above, an example method is shown to calculate the AVDpfor a CRT device. In operation310, the AVIsis measured by the CRT device. In operation320, the optimal AVDsfor sensed atrium and paced ventricle is calculated as described above. Then, in operation330, the atrium is paced for one or more beats. In operation340, the AVIpis measured. Next, the offset is calculated in operation350using Equation 2 above. Finally, in operation360, the optimal AVDpfor paced atrium and paced ventricle can be calculated using Equation 3.

Other methods can also be used to calculate an optimized AVDp. For example, U.S. patent application Ser. No. 10/243,811 to Ding et al., which is hereby incorporated by reference in its entirety, describes a method to calculate AVDpusing AVIp, according to the following Equation 4.
AVDp=K1(AVIp)−K2  (4)

The above example methods illustrated in Equations 1-4 allow for the calculation of AVDsor AVDpusing a fixed atrial sensing or pacing rate. A typical pacing system uses a standard pre-set AV delay when pacing a heart. Therefore, prior art systems do not account for changes in atrioventricular delays associated with changes in heart rate or pacing rate, or changes in the mode in which the heart is being paced (e.g., changes from atrial sensing to atrial pacing).

However, optimal AV delays can vary depending on the rate of pacing and on whether the atrium is being sensed or paced. For example, as illustrated inFIGS. 4 and 6, AVDsis usually shorter than AVDpbecause when pacing the right atrium, activation of the left atrium is further delayed. In order to maintain the appropriate contraction sequence of the left atrium and ventricle, the timing of left ventricular stimulation needs to be delayed correspondingly, which necessitates a longer AVDp.

The AV delay can have a significant impact on the hemodynamic efficiency of the heart100. AV delays of greater than or less than optimal length can cause asynchronous contraction, which can result in less oxygen-rich blood being pumped during each stroke of the heart100.

Therefore, there is a need for systems and methods that can efficiently and accurately optimize AV delay, and utilize these AV delays at different sensing and pacing rates and during different pacing modes (e.g., atrial sensing or atrial pacing).

SUMMARY

The present invention is directed to cardiac resynchronization therapy systems. More specifically, the present invention is directed to systems and methods to optimize atrioventricular delay during cardiac resynchronization therapy.

According to one aspect, embodiments of the invention relate to a cardiac resynchronization device associated with a heart, the cardiac resynchronization device including a therapy module for delivering resynchronization therapy to the heart, and a sensing module and a timer module capable of sensing and timing a plurality of atrioventricular intervals at a plurality of rates. The device also includes a controller coupled to the timer module capable of calculating a plurality of atrioventricular delays for resynchronization therapy based on the plurality of atrioventricular intervals, and a memory module capable of storing the plurality of atrioventricular delays.

According to another aspect, embodiments of the invention relate to method for optimizing atrioventricular delay for a cardiac resynchronization device, including: measuring a plurality of atrioventricular intervals of a heart at a plurality of rates; calculating an atrioventricular delay for each of the plurality of atrioventricular intervals; and storing the atrioventricular delay for each of the plurality of atrioventricular intervals in a memory of the cardiac resynchronization device.

According to yet another aspect, embodiments of the invention relate to a method for optimizing atrioventricular delay for a cardiac resynchronization device, including: pacing a heart at a first rate; measuring a first atrioventricular interval; calculating a first atrioventricular delay; storing the first atrioventricular delay in a lookup table in a memory of the cardiac resynchronization device; pacing the heart at a second rate greater than the first rate; measuring a second atrioventricular interval; calculating a second atrioventricular delay; and storing the second atrioventricular delay in the lookup table in the memory of the cardiac resynchronization device.

According to another aspect, embodiments of the invention relate to a method for optimizing atrioventricular delay for cardiac resynchronization therapy, including: measuring a first atrioventricular interval at a first pacing rate, the first atrioventricular interval spanning a first event corresponding to atrial activity of an atrium and a second event corresponding to ventricular activity of a ventricle of a heart; calculating a first atrioventricular delay based on the first atrioventricular interval; storing the first atrioventricular delay and the first pacing rate in a lookup table in a memory of a cardiac resynchronization device; measuring a second atrioventricular interval at a second pacing rate; calculating a second atrioventricular delay; and storing the second atrioventricular delay and the second pacing rate in the lookup table in the memory of the cardiac resynchronization device.

According to another aspect, embodiments of the invention relate to a method for optimizing sensed atrioventricular delay for a cardiac resynchronization device, including: measuring a first sensed rate; determining if the first sensed rate exceeds a threshold; and if the first sensed rate exceeds a threshold, determining if a first sensed atrioventricular delay has not been previously calculated or has expired for the first sensed rate. If the first sensed atrioventricular delay has not been previously calculated or has expired: measuring a first sensed atrioventricular interval; calculating the first sensed atrioventricular delay from the first sensed atrioventricular interval; and storing the first sensed atrioventricular delay in a memory of the cardiac resynchronization device.

According to yet another aspect, embodiments of the invention relate to a method for optimizing sensed and paced atrioventricular delays for a cardiac resynchronization device associated with a heart, including: measuring a sensed atrioventricular interval of the heart; pacing an atrium of the heart; measuring a paced atrioventricular interval; and calculating an offset based on the sensed atrioventricular interval and the paced atrioventricular interval.

The above summary is not intended to describe each disclosed embodiment or every implementation of the present invention. The figures and detailed description that follow more particularly exemplify embodiments of the invention. While certain embodiments will be illustrated and described, the invention is not limited to use in such embodiments.

DETAILED DESCRIPTION

The present invention generally relates to cardiac resynchronization therapy systems. More specifically, the present invention is directed to systems and methods to optimize atrioventricular delay during cardiac resynchronization therapy.

As used herein, the terms “intrinsic” and “sensed” mean the natural or unprovoked activity of the heart such as, for example, depolarization of the heart. The term “paced” is used herein to mean stimulation of the heart caused by one or more electrical impulses delivered to the heart by, for example, a cardiac rhythm management (“CRM”) system including a cardiac resynchronization therapy (“CRT”) device.

In addition, the term “atrioventricular interval,” whether sensed or paced, means an interval between an identifiable portion of atrial electrical activity and an identifiable portion of ventricular electrical activity. This interval can be measured using various methods. For example, the interval AQs* or AQp* (the interval between a sensed or paced atrial event and the onset of the ventricular electrical event) or AVIsor AVIp(the interval between a sensed or paced atrial event and a sensed ventricular electrical event) can be used to measure the atrioventricular interval. See, for example, U.S. Pat. No. 6,144,880 to Ding et al. and U.S. patent application Ser. Nos. 10/314,899 and 10/314,910 both to Yu et al. for example methods for measuring the atrioventricular interval.

Embodiments of the present invention can be used to optimize atrioventricular (“AV”) delay (“AVD”) during sensing or pacing of the atrium and for a plurality of pacing rates. In one example embodiment, a plurality of paced AV delays for different rates can be calculated. In another example embodiment, a plurality of sensed AV delays for different sensing rates can be calculated. In another embodiment, a plurality of sensed AV delays for different sensing rates are converted from paced AV delays calculated at different pacing rates. In other embodiments, the sensed AV delays for different sensing rates are calculated and populated as needed. Combinations of the various embodiments are also possible.

The present systems and methods are described with respect to implantable CRM systems, such as pacemakers, cardioverter/defibrillators, pacer/defibrillators, and multi-chamber and/or multi-site (in a single or multiple heart chambers) CRT devices. Such CRT devices are included within CRM systems even though the CRT devices need not necessarily modulate heart rate. Such CRT devices may instead provide contraction-evoking stimulations that establish or modify the conduction path of propagating depolarizations to obtain more efficient pumping of the heart. Moreover, the present systems and methods also find application in other implantable medical devices, and in unimplanted (“external”) devices, including, but not limited to, external pacemakers, cardioverter/defibrillators, pacer/defibrillators, multi-chamber and/or multi-site CRT devices, monitors, programmers, and recorders, whether such devices are used for providing a diagnostic, a therapy, or both.

The methods disclosed herein may be manually implemented by, for example, a caregiver. Alternatively, the CRT device may automatically perform one or more of the methods. The CRT device may perform one or more of the methods subsequent to implantation and prior to delivery of therapy. In addition, the CRT device may perform one or more of the methods at selected or periodic intervals in order to re-optimize operating parameters.

Referring now toFIG. 8, one embodiment illustrating various components of a CRM system205is shown along with the heart100. In this embodiment, the CRM system205includes, among other elements, CRT device206, which is coupled by leads210,211, and212to the heart100. Lead210is positioned in the right ventricle, lead211positioned in the right atrium, and lead212positioned on the left ventricle.

In one embodiment, leads210,211, and212include electrodes220,230, and290associated with the right ventricle, right atrium, and left ventricle, respectively. Each electrode is “associated” with the particular heart chamber by inserting it into that heart chamber, or by inserting it into a portion of the heart's vasculature that is close to that heart chamber, or by epicardially placing the electrode outside that heart chamber, or by any other technique of configuring and situating an electrode for sensing signals and/or providing therapy with respect to that heart chamber. Leads210,211, and212may alternatively also include ring electrodes225,235, and295. Each electrode may be used for unipolar sensing of heart signals and/or unipolar delivery of contraction-evoking stimulations in conjunction with one or more other electrodes associated with the heart100. Alternatively, bipolar sensing and/or therapy may be delivered, for example, between electrodes220and225of lead210.

The CRT device206includes a sensing module260, which is coupled to one or more of the electrodes for sensing electrical depolarizations corresponding to heart chamber activity. Such electrical depolarizations of the heart tissue include atrial depolarizations, referred to as P-waves, and ventricular depolarizations, referred to as QRS complexes. The QRS complex is a rapid sequence of several signal excursions away from a baseline in sequentially switching polarity, with the largest excursion referred to as an R-wave.

A peak detector265is coupled to the sensing module260for detecting, for example, the P-wave peak from the right atrium106, obtained by bipolar sensing between electrodes230and235, or by any other sensing technique. Peak detector265may also sense the R-wave peak at a plurality of different sites associated with the left ventricle112or right ventricle108, such as at each of the electrodes290and295. Sensing may be unipolar or bipolar. The peak detector265may detect a variety of points associated with the electrical activity of the heart100.

A timer module270is coupled to the peak detector265for timing one or more intervals between one or more events. For example, the timer module270may be used to time an interval between atrial and ventricular activity. As previously described, this interval is known as the atrioventricular (“AV”) interval (“AVI”). Because the interval is measured during sensing of the atrium and ventricle, the interval is referred to herein as the sensed atrioventricular interval (“AVIs”). The timer module270is also coupled to the therapy module285, which provides the time at which an atrial stimulation is delivered. Thus, timer module270can also measure the interval between an atrial pacing impulse and sensed ventricular activity (“AVIp”).

A controller280is coupled to the timer module270. The controller280may process the one or more intervals measured by the timer module270. For example, the controller280may implement one or more of the methods described in sections II-IV below. The controller280may store one or more calculations in a memory module282coupled to the controller280.

A therapy module285is coupled to the controller280. The controller280controls the therapy module285, and the therapy module285is configured to deliver electrical impulses to the heart100by leads210,211, and/or212. The electrical impulses may be used to stimulate activity (e.g., contraction) in one or more chambers of the heart.

The CRM system205also includes a telemetry transceiver275, which is communicatively coupled to an external programmer277. The external programmer277may remotely communicate with the telemetry transceiver275to, for example, extract data from or reprogram the CRM system205. In the example embodiments of the present invention, the external programmer277is used to control the mode and pacing of the CRM system205.

The CRT device206may operate in a variety of modes. In a first mode, VDD, the atrium106is sensed and one or both of the ventricles108and112are paced. In a second mode, DDD, both the atrium106and one or both of the ventricles108and112are paced. A switch between VDD and DDD pacing is referred to as a mode switch.

As described by one or more of the methods below, this invention relates to methods to calculate optimized sensed and/or paced AV delays at a plurality of rates. In addition, methods are provided to allow for switching to different modes (e.g., between atrial sensing and pacing) at different paced and sensed rates.

II. Optimization of Paced AV Delay for a Plurality of Atrial Pacing Rates

In accordance with an example embodiment of the invention, the paced atrioventricular delay (“AVDp”) for a plurality of pacing rates may be optimized when a CRT device is operating in a paced atrial mode (e.g., DDD mode) using one or more of the methods described below.

For example, one example method for calculating a plurality of AVDpat a plurality of pacing rates is shown inFIG. 9. In operation510, a variable N is set equal to zero. As described below, the variable N is used to increment the pacing rate. In operation520, the atrium is paced at a rate that is incremented according to Equation 5.
Pacing Rate=X+KN(5)
The variable X is the resting heart rate or lowest desired heart rate of the individual. K is a constant used to control the steps taken between adjacent AVIpreadings. For example, in one embodiment, the constant K is set at 5, so that the pacing rate is incremented by 5 beats for each measured AVIp. Other constants may also be used. For example, K can be set equal to 1 if it is desirable to measure the AVIpfor each pacing rate or may be increased to greater than 5 if less readings are desired.

With N set equal to 1 for the first loop of the method, the heart is paced at a rate of X+K. Next, in operation530, the AVIpfor the given pacing rate (“AVINp”) is measured. Next, in operation540, the AVDpfor the given pacing rate (“AVDNp”) is calculated. The AVDNpmay be calculated using, for example, an equation similar to Equation 4 described above.

Once the AVDNpis calculated, the AVDNpand associated pacing rate are stored in CRT device memory in operation550. Then, in operation560, the current pacing rate is compared to a maximum pacing rate. This maximum pacing rate may be set to any desired value, such as, for example, 180 beats/minute. If the current pacing rate meets or exceeds the maximum rate, the measurements are complete. If the maximum rate has not been reached, in operation570the variable N is incremented and control is passed back to operation520for a second loop of the method.

During the second loop of the method, the pacing rate is calculated according to Equation 5. A new AVINpat the new pacing rate is measured in operation530, and a new AVDNpis calculated in operation540. The AVDNpand associated pacing rate are also stored in memory in operation550. The method is continued until the maximum pacing rate is reached.

The AVDNpfor each pacing rate that is stored in memory of the CRT device may be assembled in a lookup table similar to Table 1 shown below.

A CRT device may utilize a table such as Table 1 to look up an optimal AVDpdepending on the current atrial pacing rate. As the CRT device pacing rate changes, the CRT device can lookup the appropriate AVDp, thereby maintaining an optimal AVDpas the pacing rate changes.

III. Optimization of Sensed AV Delay for a Plurality of Sensed Rates

In accordance with other embodiments of the invention, the AVDscan be optimized for a plurality of sensed heart rates when a CRT device is operating in a sensed atrial mode (e.g., VDD mode). This may be advantageous, for example, for patients exhibiting normal sinus node function but requiring CRT.

For example, a method is illustrated inFIG. 10Afor calculating a plurality of different AVDsat a plurality of sensed heart rates. In operation810, the current sensed atrial rate is measured. Next, in operation820, if the current sensed atrial rate has not exceeded the threshold, control is passed back to operation810. If the current sensed atrial rate has exceed the threshold, control is passed to operation830, where it is determined whether or not the AVDNsfor the current sensed atrial rate XNhas been previously calculated or is expired.

If the AVDNsassociated with the current sensed atrial rate XNhas not been previously calculated, control is passed to operation840, and the AVINsat the current sensed rate X1is measured. Next, in operation850, the AVDNsfor the particular sensed rate is estimated (using, for example, Equation 1 above) and stored, for example, in a table such as Table 2 below.

TABLE 2Sensed rateOptimized AVDsX1AVD1sX2AVD2sX3AVD3sX4AVD4sX5AVD5sX6AVD6s
In addition, if the AVDNsassociated with the current sensed atrial rate XNhas been previously calculated but has expired, control is passed to operation850, where the AVDNsis recalculated and stored in Table 2. The AVDNscan be set to expire at a certain interval after calculation such as, for example, one week, one month, two months, etc., so that if the sensed atrial rate is reached after expiration of the interval, the AVDNscan be recalculated. Control is then passed back to operation810.

If it is determined in operation830that the current sensed atrial rate XNhas been previously calculated and has not expired, control is passed back to operation810to continue measuring the current sensed atrial rate.

In this manner, the AVDNscan be populated in Table 2 as each sensed atrial rate is reached as the patient's heart rate intrinsically fluctuates. Therefore, the values for the AVDNsare advantageously populated “on the fly.” In addition, the values for the AVDNscan be recalculated at set intervals to account for changes in the patient's condition over time.

Another example method for estimating a plurality of AVDsat a plurality of atrial pacing rates is shown inFIG. 10B. In operation605, the AVIsis measured at a first sensed rate, typically a resting heart rate. Then, in operation610the AVDsis calculated using a known method described above and stored in memory in operation612. Next, in operation615, the heart is paced at a rate X slightly higher than the initial sensed rate. In operation620, the AVIpis measured, and an offset is calculated in operation625using AVIpand AVIs. See Equation 2 above.

Next, in operation635the variable N is set equal to 1, and the atrium is paced at a rate calculated in operation640according to Equation 5. Then, in operation645, the AVINpis measured for the paced rate, and AVDNpis calculated in operation647using a known method as describe above. Next, an AVINsis estimated in operation650using Equation 6, a modified form of Equation 2.
AVINs=AVINp−offset  (6)

Then, in operation655, an AVDNsbased on the AVINscan be calculated using, for example, one or more of the methods described above. The AVDNsas well as AVDNpand associated rate are stored in operation657. In operation660, the CRT device determines whether a maximum pacing rate has been reached. If the maximum rate has been reached, the measurements are complete and the atrial test pacing is ceased. If the maximum rate has not been reached, the variable N is incremented and control is passed back to operation640for a new set of measurements and calculation of a new AVDNs(and ADVNp) at a higher pacing rate.

Once all measurements are completed, the CRT device206may create a table, such as example Table 3 illustrated below, including the AVDNsand AVDNpfor each pacing rate. A CRT device may utilize such a table to look up an optimal AVDsor AVDpdepending on the sensed/paced atrial rate. As the atrial sensed or paced rate changes, the CRT device206can lookup the appropriate AVDsor ADVp, thereby maintaining an optimal AVDsor AVDpas the sensed or paced rate changes.

Knowing both the AVDsand AVDpfor a particular patient can be important because a CRT device may undergo a mode switch during use. A mode switch can include a switch from atrial pacing to atrial sensing such as, for example, when a patient changes status from resting to exercising. During such a mode switch from pacing to sensing (or vice versa), the CRT device should switch from the optimized AVDpto the optimized AVDsof the CRT device, thereby continuing to maintain an optimized AVD.

For example, an operation flow for an example CRT device is shown inFIG. 11. In operation410, CRT is applied to a patient. In operation420, the CRT device determines if a mode switch has occurred. The mode switch may be from atrial sensing to pacing, or atrial pacing to sensing. If a mode switch has occurred, control is passed to operation430, wherein the device determines the current mode in which the CRT device is operating. If the CRT device is now operating in atrial sensing mode, control is passed to operation450and the optimized AVDsis selected. Conversely, if the CRT device is now operating in atrial pacing mode, control is passed to operation460and the optimized AVDpis selected. In this manner, AVD may be optimized before and after a mode switch.

For example, a flow diagram shown inFIG. 12illustrates how a CRT device may utilize lookup tables including a plurality of AVDNpand AVDNs. In operation710, an appropriate AVDsbased on a current pacing or sensing rate, is selected. An appropriate AVD is selected, for example, by looking up the AVD in either a pacing lookup table or a sensing lookup table stored on the CRT device. If the CRT is functioning in sensing mode, the current sensed rate is used to select an appropriate AVDsfrom the sensing lookup table. Alternatively, if the CRT device is functioning in pacing mode, the current pacing rate is used to select an appropriate AVDpfrom the pacing lookup table.

Next, in operation720, CRT is applied. In operation730, the CRT device determines whether there has been a mode switch, either from sensing to pacing or from pacing to sensing. If a mode switch has occurred, control is passed to740, wherein the current mode is determined. If the current mode is sensing, control is passed to operation760, in which an appropriate AVDsfrom the sensing lookup table for the current pacing rate is selected. If the current mode is pacing, control is passed to operation765, in which an appropriate AVDpfrom the pacing lookup table for the current pacing rate is selected. After selecting an appropriate AVDsor AVDp, control is passed back to operation720and CRT continues.

If, in operation730, the CRT device determines that a mode switch has not occurred, control is passed to operation735, in which the CRT device determines if the current pacing rate has changed. If the pacing rate has changed, control is passed to operation710, in which a new AVD is looked up in either the sensing or pacing lookup table. If, in operation735, the pacing rate has not changed, control is passed back to operation720and CRT continues.

The above systems and methods can be modified without departing from the inventive concepts disclosed herein. For example, instead of calculating a plurality of AVDsat different pacing rates as described in section III above, it may only be necessary to calculate two AVDs, one at a low pacing rate and one at a high pacing rate. Using these two AVDs, it may be possible to interpolate the remaining values, assuming a relationship such as a linear relationship between AVDsfor different sensed rates. In addition, other methods besides those illustrated above can be used to calculate an optimal AVDsand AVDp.

The logical operations for calculating the optimized AVDsmay be performed by a device other than an implanted CRT device206. For example, an external device programmer, communicating via telemetry, may be used. Furthermore, the logical operations may be implemented (1) as a sequence of computer implemented steps running on a computer system, and/or (2) as interconnected machine modules.

This implementation is a matter of choice dependent on the performance requirements of the device206or device programmer implementing the invention. Accordingly, the logical operations making up the embodiments of the invention described herein are referred to 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.