Patent Grant
7236824
The present invention relates to the field of implantable medical devices, more particularly, to cardiac pacing systems having nodal rhythm detection and treatment.
Implantable cardiac pacing systems deliver a pacing signal to stimulate a heart chamber. The pacing signal is typically delivered by an electrode in the heart chamber. The same electrode is also used to sense electrical activity indicating an intrinsic contraction of the heart chamber. The presence or absence of the sensed and the timing of the sensed contractions, are used to control the cardiac pacing system for the patient's well being.
In AV nodal rhythm, the intrinsic AV pacemaker controls the ventricles and atria. The nodal rhythm can result from anything that suppresses sinus node activity, such as sinus bradycardia; any form of vagal stimulation; digitalis; the initial phase of atropine action; SA block; or congenital absence of the SA node. The AV nodal rate will usually be less than 50 beats per minute.
AV nodal rhythm may also occur from anything that enhances AV nodal rhythm, such as digitalis intoxication, rheumatic fever, or inferior myocardial infarction. The AV nodal rate will usually be between 60 and 100 beats per minute. This is also called accelerated AV (nodal) rhythm.
Sherlag et al. present evidence of that there are at least two varieties of AV junctional rhythm: true AV nodal rhythm of 30 to 40 bpm increased under influence of atropine, and His bundle rhythm of 20 to 25 bpm little affected by atropine. Scherlag, B. J., Lazzara, R. Helfant, R. H., Differentiation of A-V Junctional Rhythms, Circulation, 48:304, 1973.
Currently AV nodal rhythm can be treated with medication, or by cardiac stimulation. Medication may be ineffective or have undesirable effects. Surgical intervention can be used to remove or reduce the AV conduction system, but runs the risks inherent in any surgical procedure, as well as uncertainty as to result.
During AV nodal rhythm, atrial contraction takes place during ventricular contraction. The blood in the atria is forced back into the venous system and may cause clinical symptoms such as venous pulsations in the jugular area and in the abdomen. Through an increased venous pressure because of the regurgitation into the venous system, inappropriate baroreceptor reflexes may cause acute drops in blood pressure.
The most pertinent prior art references known at the present time are the following:
In “Transesophageal Atrial Pacing For Intraoperative Sinus Bradycardia Or AV Junctional Rhythm: Feasibility As Prophylaxis In 200 Anesthetized Adults And Hemodynamic Effects Of Treatment,” Atlee et al., J Cardiothorac Vasc Anesth 1993 August; 7(4):436-41, Atlee et al. reported that transesophageal atrial pacing (TAP) at a rate sufficient to overdrive atrioventricular junctional rhythm (AVJR) was effective initial treatment in all patients tested. Feasibility of TAP as prophylaxis for sinus bradycardia (SB) or AVJR was tested with approved or investigational devices in 200 anesthetized surgical patients, not necessarily with cardiovascular disease or having cardiac surgery. Thirteen patients had AVJR (72+/−4 beats/min; mean+/−SEM).
In “The Effects Of Overdrive Pacing And Lidocaine On Atrioventricular Junctional Rhythm In Man: The Role Of Abnormal Automaticity,” Tenczer et al., Circulation 1985 September; 72(3):480-6, Tenczer et al. reported AV junctional rhythms in group I (17 patients) were suppressed by overdrive pacing, and their rates were decreased by lidocaine. AV junctional rhythms in group II (five patients) were not suppressed by overdrive pacing. The data suggest that AV junctional rhythms in group I were caused by normal automaticity, while those in group II were probably due to abnormal automaticity.
All prior art references above are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, the Detailed Description of the Preferred Embodiments and the Claims set forth below, many of the devices and methods disclosed in the prior art references may be modified advantageously by using the teachings of the present invention.
The present invention is therefore directed to providing a system and method for nodal rhythm detection and treatment. The system of the present invention overcomes the problems, disadvantages and limitations of the prior art described above, and provides a more efficient and accurate means of nodal rhythm detection and treatment.
The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the prior art of nodal rhythm detection and treatment. Those problems include, without limitation: (a) need for automatic nodal rhythm detection, (b) need for automatic nodal rhythm treatment, (c) interference with intrinsic heart rhythm, (d) patient discomfort from pacemaker syndrome, and (e) patient discomfort from abrupt changes after treatment.
In comparison to known techniques for nodal rhythm detection and treatment, various embodiments of the present invention provide one or more of the following advantages: (a) the ability to automatically detect nodal rhythm, (b) the ability to automatically treat nodal rhythm using atrial pacing tuned by the AV delay, and (c) the ability to restore the intrinsic heart rhythm with an optimized hemodynamic AV delay.
Some of the embodiments of the present invention include one or more of the following features: (a) an IMD having automatic nodal rhythm detection, (b) an IMD having automatic nodal rhythm treatment that use atrial pacing tuned by the AV delay, (c) methods of performing nodal rhythm detection that use a nodal activity window, (d) methods of performing automatic nodal rhythm treatment that use atrial pacing tuned by the AV delay, and (e) methods of avoiding patient discomfort from AV nodal rhythm.
At least some embodiments of the present invention involve detecting nodal activity by looking for atrial activity in a nodal activity window around ventricular activity. If a predetermined number of successive atrial events fall within the nodal activity window, nodal rhythm is present. The nodal activity window is typically 60 ms before and 100 ms after a ventricular sense, but may be shorter and can be tuned for a specific patient. The nodal activity detection method first determines if the atrial event precedes the ventricular event (positive AV delay) or vice versa (VA delay), then looks for atrial activity between a first time limit and the ventricular activity if the atrial event precedes the ventricular event (positive AV delay), and for atrial activity between a second time limit and the ventricular activity if the ventricular event precedes the atrial event (positive VA delay). The nodal activity detection method can also calculate an appropriate initial atrial escape interval for nodal treatment if pacing is to be applied. If atrial activity occurs outside the nodal activity window before the predetermined number of successive atrial events is reached, the nodal rhythm detection counter is reset and the nodal activity detection method starts over.
Other embodiments of the present invention involve detecting nodal activity, then treating the nodal activity using pacing. The nodal rhythm detection and treatment method starts by checking for tachycardia and average ventricular rate greater than 100 beats per minute, then terminates the nodal treatment if either is found because nodal rhythm could not be occurring with those conditions. If neither condition is present, the nodal rhythm detection and treatment method checks to see if nodal treatment is active, then looks for nodal rhythm using a nodal activity detection method if it is not.
If nodal treatment is active, the nodal treatment follows different procedures depending on whether the activity is an atrial sense, an atrial pace followed by a ventricular sense, or an atrial pace followed by a ventricular pace.
An atrial sense may indicate that the nodal rhythm is in control and further adjustment of the atrial escape interval is required. The nodal treatment method looks for atrial activity in a nodal activity window around ventricular activity. The nodal activity window is typically 60 ms before and 100 ms after a ventricular sense, but may be shorter and can be tuned for a specific patient. Depending on the timing of the ventricular sense with respect to the atrial sense, the nodal treatment method calculates a new atrial escape interval to tune the atrial escape interval.
An atrial pace followed by a ventricular sense indicates that the therapy is effective. The next AV delay is further tuned based on the last ventricular sense. An atrial pace followed by a ventricular pace indicates the nodal rhythm has stopped. The pacing enters a flywheel mode in which the pacing interval is gradually increased to ease out of nodal treatment. If a predetermined number of successive atrial pace-ventricular pace sequences occur, nodal rhythm is no longer present and the nodal treatment is deactivated.
The above, and other objects, advantages and features of the present invention will be more readily understood from the following detailed description of the preferred embodiments thereof, when considered in conjunction with the drawings, in which like reference numerals indicate identical structures throughout the several views, and wherein:
IMD 10 in
As shown in
Microcomputer circuit 58 preferably comprises on-board circuit 60 and off-board circuit 62. Circuit 58 may correspond to a microcomputer circuit disclosed in U.S. Pat. No. 5,312,453 to Shelton et al., hereby incorporated by reference herein in its entirety. On-board circuit 60 preferably includes microprocessor 64, system clock circuit 66 and on-board RAM 68 and ROM 70. Off-board circuit 62 preferably comprises a RAM/ROM unit. On-board circuit 60 and off-board circuit 62 are each coupled by data communication bus 72 to digital controller/timer circuit 74. Microcomputer circuit 58 may comprise a custom integrated circuit device augmented by standard RAM/ROM components.
Electrical components shown in
Continuing to refer to
Digital controller/timer circuit 74 is preferably coupled to sensing circuitry, including sense amplifier 88, peak sense and threshold measurement unit 90 and comparator/threshold detector 92. Circuit 74 is further preferably coupled to electrogram (EGM) amplifier 94 for receiving amplified and processed signals sensed by lead 18. Sense amplifier 88 amplifies sensed electrical cardiac signals and provides an amplified signal to peak sense and threshold measurement circuitry 90, which in turn provides an indication of peak sensed voltages and measured sense amplifier threshold voltages on multiple conductor signal path 67 to digital controller/timer circuit 74. An amplified sense amplifier signal is then provided to comparator/threshold detector 92. By way of example, sense amplifier 88 may correspond to that disclosed in U.S. Pat. No. 4,379,459 to Stein, hereby incorporated by reference herein in its entirety.
The electrogram signal provided by EGM amplifier 94 is employed when IMD 10 is being interrogated by an external programmer to transmit a representation of a cardiac analog electrogram. See, for example, U.S. Pat. No. 4,556,063 to Thompson et al., hereby incorporated by reference herein in its entirety. Output pulse generator 96 provides pacing stimuli to patient's heart 8 through coupling capacitor 98 in response to a pacing trigger signal provided by digital controller/timer circuit 74 each time the escape interval times out, an externally transmitted pacing command is received or in response to other stored commands as is well known in the pacing art. By way of example, output amplifier 96 may correspond generally to an output amplifier disclosed in U.S. Pat. No. 4,476,868 to Thompson, hereby incorporated by reference herein in its entirety.
The specific embodiments of input amplifier 88, output amplifier 96 and EGM amplifier 94 identified herein are presented for illustrative purposes only, and are not intended to be limiting in respect of the scope of the present invention. The specific embodiments of such circuits may not be critical to practicing some embodiments of the present invention so long as they provide means for generating a stimulating pulse and are capable of providing signals indicative of natural or stimulated contractions of heart 8.
In some preferred embodiments of the present invention, IMD 10 may operate in various non-rate-responsive modes, including, but not limited to, DDD, DDI, VVI, VOO and VVT modes. In other preferred embodiments of the present invention, IMD 10 may operate in various rate-responsive, including, but not limited to, DDDR, DDIR, VVIR, VOOR and VVTR modes. Some embodiments of the present invention are capable of operating in both non-rate-responsive and rate responsive modes. Moreover, in various embodiments of the present invention IMD 10 may be programmably configured to operate so that it varies the rate at which it delivers stimulating pulses to heart 8 only in response to one or more selected sensor outputs being generated. Numerous pacemaker features and functions not explicitly mentioned herein may be incorporated into IMD 10 while remaining within the scope of the present invention.
The present invention is not limited in scope to single-sensor or dual-sensor pacemakers, and is not limited to IMD's comprising activity or pressure sensors only. Nor is the present invention limited in scope to single-chamber pacemakers, single-chamber leads for pacemakers or single-sensor or dual-sensor leads for pacemakers. Thus, various embodiments of the present invention may be practiced in conjunction with more than two leads or with multiple-chamber pacemakers, for example. At least some embodiments of the present invention may be applied equally well in the contexts of single-, dual-, triple- or quadruple-chamber pacemakers or other types of IMD's. See, for example, U.S. Pat. No. 5,800,465 to Thompson et al., hereby incorporated by reference herein in its entirety, as are all U.S. patents referenced therein.
IMD 10 may also be a pacemaker-cardioverter-defibrillator (“PCD”) corresponding to any of numerous commercially available implantable PCDs. Various embodiments of the present invention may be practiced in conjunction with PCDs such as those disclosed in U.S. Pat. No. 5,545,186 to Olson et al., U.S. Pat. No. 5,354,316 to Keimel, U.S. Pat. No. 5,314,430 to Bardy, U.S. Pat. No. 5,131,388 to Pless and U.S. Pat. No. 4,821,723 to Baker et al., all hereby incorporated by reference herein, each in its respective entirety.
The atrial/SVC lead shown in
The coronary sinus lead shown in
Implantable PCD 10 is shown in
IMD 10 is provided with an electrode system. If the electrode configuration of
Electrodes 2 and 3 are located on or in the ventricle and are coupled to the R-wave amplifier 37, which preferably takes the form of an automatic gain controlled amplifier providing an adjustable sensing threshold as a function of the measured R-wave amplitude. A signal is generated on R-out line 39 whenever the signal sensed between electrodes 2 and 3 exceeds the present sensing threshold.
Electrodes 9 and 13 are located on or in the atrium and are coupled to the P-wave amplifier 43, which preferably also takes the form of an automatic gain controlled amplifier providing an adjustable sensing threshold as a function of the measured P-wave amplitude. A signal is generated on P-out line 45 whenever the signal sensed between electrodes 9 and 13 exceeds the present sensing threshold. The general operation of R-wave and P-wave amplifiers 37 and 43 may correspond to that disclosed in U.S. Pat. No. 5,117,824, by Keimel et al., issued Jun. 2, 1992, for “An Apparatus for Monitoring Electrical Physiologic Signals”, hereby incorporated by reference herein in its entirety.
Switch matrix 47 is used to select which of the available electrodes are coupled to wide band (0.5-200 Hz) amplifier 49 for use in digital signal analysis. Selection of electrodes is controlled by the microprocessor 51 via data/address bus 53, which selections may be varied as desired. Signals from the electrodes selected for coupling to bandpass amplifier 49 are provided to multiplexer 55, and thereafter converted to multi-bit digital signals by A/D converter 57, for storage in random access memory 59 under control of direct memory access circuit 61. Microprocessor 51 may employ digital signal analysis techniques to characterize the digitized signals stored in random access memory 59 to recognize and classify the patient's heart rhythm employing any of the numerous signal processing methodologies known to the art.
The remainder of the circuitry is dedicated to the provision of cardiac pacing, cardioversion and defibrillation therapies, and, for purposes of the present invention may correspond to circuitry known to those skilled in the art. The following exemplary apparatus is disclosed for accomplishing pacing, cardioversion and defibrillation functions. Pacer timing/control circuitry 63 preferably includes programmable digital counters which control the basic time intervals associated with DDD, VVI, DVI, VDD, AAI, DDI and other modes of single and dual chamber pacing well known to the art. Circuitry 63 also preferably controls escape intervals associated with anti-tachyarrhythmia pacing in both the atrium and the ventricle, employing any anti-tachyarrhythmia pacing therapies known to the art.
Intervals defined by pacing circuitry 63 include atrial and ventricular pacing escape intervals, the refractory periods during which sensed P-waves and R-waves are ineffective to restart timing of the escape intervals and the pulse widths of the pacing pulses. The durations of these intervals are determined by microprocessor 51, in response to stored data in memory 59 and are communicated to pacing circuitry 63 via address/data bus 53. Pacer circuitry 63 also determines the amplitude of the cardiac pacing pulses under control of microprocessor 51.
During pacing, escape interval counters within pacer timing/control circuitry 63 are reset upon sensing of R-waves and P-waves as indicated by a signals on lines 39 and 45, and in accordance with the selected mode of pacing on time-out trigger generation of pacing pulses by pacer output circuitry 65 and 67, which are coupled to electrodes 9, 13, 2 and 3. Escape interval counters are also reset on generation of pacing pulses and thereby control the basic timing of cardiac pacing functions, including anti-tachyarrhythmia pacing. The durations of the intervals defined by escape interval timers are determined by microprocessor 51 via data/address bus 53. The value of the count present in the escape interval counters when reset by sensed R-waves and P-waves may be used to measure the durations of R-R intervals, P-P intervals, P-R intervals and R-P intervals, which measurements are stored in memory 59 and used to detect the presence of tachyarrhythmias.
Microprocessor 51 most preferably operates as an interrupt driven device, and is responsive to interrupts from pacer timing/control circuitry 63 corresponding to the occurrence sensed P-waves and R-waves and corresponding to the generation of cardiac pacing pulses. Those interrupts are provided via data/address bus 53. Any necessary mathematical calculations to be performed by microprocessor 51 and any updating of the values or intervals controlled by pacer timing/control circuitry 63 take place following such interrupts.
Detection of atrial or ventricular tachyarrhythmias, as employed in the present invention, may correspond to tachyarrhythmia detection algorithms known in the art. For example, the presence of an atrial or ventricular tachyarrhythmia may be confirmed by detecting a sustained series of short R-R or P-P intervals of an average rate indicative of tachyarrhythmia or an unbroken series of short R-R or P-P intervals. The suddenness of onset of the detected high rates, the stability of the high rates, and a number of other factors known in the art may also be measured at this time. Appropriate ventricular tachyarrhythmia detection methodologies measuring such factors are described in U.S. Pat. No. 4,726,380 issued to Vollmann, U.S. Pat. No. 4,880,005 issued to Pless et al. and U.S. Pat. No. 4,830,006 issued to Haluska et al., all incorporated by reference herein, each in its respective entirety. An additional set of tachycardia recognition methodologies is disclosed in the article “Onset and Stability for Ventricular Tachyarrhythmia Detection in an Implantable Pacer-Cardioverter-Defibrillator” by Olson et al., published in Computers in Cardiology, Oct. 7-10, 1986, IEEE Computer Society Press, pages 167-170, also incorporated by reference herein in its entirety. Atrial fibrillation detection methodologies are disclosed in Published PCT Application Ser. No. US92/02829, Publication No. WO92/18198, by Adams et al., and in the article “Automatic Tachycardia Recognition”, by Arzbaecher et al., published in PACE, May-June, 1984, pp. 541-547, both of which are incorporated by reference herein in their entireties.
In the event an atrial or ventricular tachyarrhythmia is detected and an anti-tachyarrhythmia pacing regimen is desired, appropriate timing intervals for controlling generation of anti-tachyarrhythmia pacing therapies are loaded from microprocessor 51 into the pacer timing and control circuitry 63, to control the operation of the escape interval counters therein and to define refractory periods during which detection of R-waves and P-waves is ineffective to restart the escape interval counters.
Alternatively, circuitry for controlling the timing and generation of anti-tachycardia pacing pulses as described in U.S. Pat. No. 4,577,633, issued to Berkovits et al. on Mar. 25, 1986, U.S. Pat. No. 4,880,005, issued to Pless et al. on Nov. 14, 1989, U.S. Pat. No. 4,726,380, issued to Vollmann et al. on Feb. 23, 1988 and U.S. Pat. No. 4,587,970, issued to Holley et al. on May 13, 1986, all of which are incorporated herein by reference in their entireties, may also be employed.
In the event that generation of a cardioversion or defibrillation pulse is required, microprocessor 51 may employ an escape interval counter to control timing of such cardioversion and defibrillation pulses, as well as associated refractory periods. In response to the detection of atrial or ventricular fibrillation or tachyarrhythmia requiring a cardioversion pulse, microprocessor 51 activates cardioversion/defibrillation control circuitry 29, which initiates charging of the high voltage capacitors 33 and 35 via charging circuit 69, under the control of high voltage charging control line 71. The voltage on the high voltage capacitors is monitored via VCAP line 73, which is passed through multiplexer 55 and in response to reaching a predetermined value set by microprocessor 51, results in generation of a logic signal on Cap Full (CF) line 77 to terminate charging. Thereafter, timing of the delivery of the defibrillation or cardioversion pulse is controlled by pacer timing/control circuitry 63. Following delivery of the fibrillation or tachycardia therapy microprocessor 51 returns the device to a cardiac pacing mode and awaits the next successive interrupt due to pacing or the occurrence of a sensed atrial or ventricular depolarization.
Several embodiments of appropriate systems for the delivery and synchronization of ventricular cardioversion and defibrillation pulses and for controlling the timing functions related to them are disclosed in U.S. Pat. No. 5,188,105 to Keimel, U.S. Pat. No. 5,269,298 to Adams et al. and U.S. Pat. No. 4,316,472 to Mirowski et al., hereby incorporated by reference herein, each in its respective entirety. Any known cardioversion or defibrillation pulse control circuitry is believed to be usable in conjunction with various embodiments of the present invention, however. For example, circuitry controlling the timing and generation of cardioversion and defibrillation pulses such as that disclosed in U.S. Pat. No. 4,384,585 to Zipes, U.S. Pat. No. 4,949,719 to Pless et al., or U.S. Pat. No. 4,375,817 to Engle et al., all hereby incorporated by reference herein in their entireties, may also be employed.
Continuing to refer to
An example of circuitry which may be used to control delivery of monophasic pulses is disclosed in U.S. Pat. No. 5,163,427 to Keimel, also incorporated by reference herein in its entirety. Output control circuitry similar to that disclosed in U.S. Pat. No. 4,953,551 to Mehra et al. or U.S. Pat. No. 4,800,883 to Winstrom, both incorporated by reference herein in their entireties, may also be used in conjunction with various embodiments of the present invention to deliver biphasic pulses.
Alternatively, IMD 10 may be an implantable nerve stimulator or muscle stimulator such as that disclosed in U.S. Pat. No. 5,199,428 to Obel et al., U.S. Pat. No. 5,207,218 to Carpentier et al. or U.S. Pat. No. 5,330,507 to Schwartz, or an implantable monitoring device such as that disclosed in U.S. Pat. No. 5,331,966 issued to Bennet et al., all of which are hereby incorporated by reference herein, each in its respective entirety. The present invention is believed to find wide application to any form of implantable electrical device for use in conjunction with electrical leads.
If the V-A interval (VAint) is within the second time limit (here, 100 ms) indicating that there may be nodal rhythm present, the method proceeds to block 108, which increments the nodal rhythm detection counter (nn). The nodal rhythm detection counter is checked against the nodal treatment activation constant (Nca) at block 110 and the nodal rhythm detection method ends at block 112 if the nodal rhythm detection counter is less than the Nca. The Nca is selected depending on the particular patient, but can be between 1 and 10, and is typically 3.
If the nodal rhythm detection counter is greater than the Nca, nodal rhythm treatment is activated. The method calculates a new atrial escape interval (A_esc) in block 114 such that the next atrial pace is delivered at a preferred AV delay before the expected ventricular sense. This is calculated as the mean ventricular rate, less the paced AV interval less the VA interval [A_esc=MVR−PAV−VAint]. The variables can be selected from the average over the successive nodal rhythm events or can be from the last set of data on reaching the Nca. The delivered PAV ranges from 90-250 ms is rate dependent and has a typical value of 150 ms. If nodal rhythm treatment is initiated, the reduced atrial escape interval will be set to a rate to terminate the nodal rhythm. A flag is set at block 116 to activate nodal rhythm treatment, the nodal rhythm detection counter (nn) is cleared at block 118, and the nodal rhythm detection method ends at block 112.
The logic is similar if the atrial event precedes the ventricular event (positive AV delay) at block 102. If the atrial event preceded the ventricular event, the method proceeds to block 120. Block 120 checks if the AV interval, the interval between the atrial event and ventricular event, is within the first time limit and may indicate a potential nodal rhythm. If the AV interval (AVint) is not within the second time limit (here, 60 ms) indicating that there is no nodal rhythm present, the method proceeds to block 106, which clears the nodal rhythm detection counter (nn) and the nodal rhythm detection method ends at block 112.
If the AV interval (AVint) is within the second time limit (here, 60 ms) indicating that there may be nodal rhythm present, the method proceeds to block 122, which increments the nodal rhythm detection counter (nn). The nodal rhythm detection counter is checked against the Nca at block 124 and the nodal rhythm detection method ends at block 112 if the nodal rhythm detection counter is less than the Nca. The Nca is selected depending on the particular patient, but can be between 1 and 10, and is typically 3.
If the nodal rhythm detection counter is greater than the Nca, nodal rhythm treatment should be activated. The method calculates a new atrial escape interval (A_esc) in block 126 as the mean ventricular rate, less the paced AV interval, plus the VA interval [A_esc=MVR−PAV+AVint]. The variables can be selected from the average over the successive nodal rhythm events or can be from the last set of data on reaching the Nca. The delivered PAV ranges from 90-250 ms is rate dependent and has a typical value of 150 ms. If nodal rhythm treatment is initiated, the reduced atrial escape interval will be set to rate to terminate the nodal rhythm. A flag is set at block 128 to activate nodal rhythm treatment, the nodal rhythm detection counter (nn) is cleared at block 130, and the nodal rhythm detection method ends at block 112. The nodal rhythm detection method as described can be used in the nodal treatment method described in
The nodal rhythm detection and treatment method starts at block 140 of
If nodal therapy is active, the method enters the nodal treatment portion of the nodal rhythm detection and treatment method at block 152. The nodal treatment portion maintains the mean ventricular rate (VVrate), and tries to restore the physiologic AVdelay. This is accomplished by delivering atrial paces at a physiologic AVdelay before the expected Vsense. Block 152 determines if the atrial event is an atrial pace or an atrial sense.
If the atrial event is an atrial pace, the method proceeds to block 154, which determines if the ventricular event is a ventricular pace or a ventricular sense. If the ventricular event is a ventricular sense, the pacing is not yet in control and further nodal treatment is required. The method proceeds to block 176 where a new atrial escape interval (A_esc) is calculated, and the sinus rhythm counter (ns) is cleared at block 178.
If in block 154 the ventricular event is a ventricular pace, the nodal rhythm might have stopped. A flywheel down is initiated at block 156. The flywheel mode allows the pacing interval to gradually ease out of nodal treatment, rather than making an abrupt change that might cause patient concern or discomfort. The atrial escape is adjusted so the next atrial pace will be delivered at a longer interval. The method then proceeds to block 158 where the nodal counter (no) is incremented.
Block 160 checks to see if the nodal counter is greater than the predetermined nodal treatment pace deactivation constant (Npd). The Npd is selected depending on the particular patient, but can be between 1 and 10, and is typically 3. If the nodal counter is not greater than the Npd, the method returns to the start at block 140. If the nodal counter is greater than the Npd, nodal treatment is no longer required, so nodal treatment is deactivated at block 162 and the nodal counter (no) is cleared at block 164.
If block 152 determines if the atrial event is an atrial sense, the method proceeds to block 166, which starts the portion of the procedure that determines whether the atrial sense originated from the atrium or the AV node. The logic is similar to the nodal rhythm detection method presented in
Block 166 checks whether the atrial event preceded the ventricular event. If the ventricular event preceded the atrial event, the answer is no and the method proceeds to block 180. Block 180 checks if the V-A interval, the interval between the ventricular event and atrial event, is within the second time limit and may indicate a potential nodal rhythm. If the V-A interval (VAint) is not within the second time limit (here, 100 ms) indicating that there is no nodal rhythm present, the method proceeds to block 170, which increments the sinus rhythm counter (ns).
Block 172 checks to see if the sinus rhythm counter is greater than the predetermined nodal treatment sinus deactivation constant (Nsd). The Nsd is selected depending on the particular patient, but can be between 1 and 10, and is typically 3. If the sinus rhythm counter is not greater than Nsd, the method returns to the start at block 140. If the sinus rhythm counter is greater than Nsd, sinus rhythm has been established and nodal treatment is no longer required, so nodal treatment is deactivated at block 174.
If the V-A interval (VAint) is within the second time limit (here, 100 ms) indicating that there may be nodal rhythm present, the method proceeds to block 182, which calculates a new escape interval. The method calculates a new atrial escape interval (A_esc) as the mean ventricular rate, less the paced AV interval less the V-A interval [A_esc=MVR−PAV−VAint]. The sinus rhythm counter (ns) is cleared at block 184.
The logic is similar at block 166 if the atrial event precedes the ventricular event (positive AV delay), only the method looks for atrial events within the first time limit of the ventricular event. If the atrial event preceded the ventricular event, the method proceeds to block 168. Block 168 checks if the A-V interval, the interval between the atrial event and ventricular event, is within the first time limit and may indicate a potential nodal rhythm. If the A-V interval (AVint) is not within the second time limit (here, 60 ms) indicating that there is no nodal rhythm present, the method proceeds to block 170, which increments the sinus rhythm counter (ns).
Block 172 checks to see if the sinus rhythm counter is greater Nsd. If the sinus rhythm counter is not greater than Nsd, the method returns to the start at block 140. If the sinus rhythm counter is greater than the Nsd, sinus rhythm has been established and nodal treatment is no longer required, so nodal treatment is deactivated at block 174.
If the A-V interval (AVint) is within the second time limit (here, 60 ms) indicating that there may be nodal rhythm present, the method proceeds to block 176, which calculates a new escape interval. This point may also be reached from block 154 if an atrial pace was followed by a ventricular sense. The method calculates a new atrial escape interval (A_esc) which is tuned such that an hemodynamic AV delay is obtained, as the mean ventricular rate, less the paced AV interval, plus the V-A interval [A_esc=MVR−PAV+VAint]. The sinus rhythm counter (ns) is cleared at block 178.
Using the “Asense, FFsense, Vsense (nodal rhythm)” case as an example, the (intrinsic) nodal activity is initiated at the AV node between the atrium and the ventricle. The atrial sense, then the far field sense, is detected in the atrium. The ventricular sense is then detected in the ventricle. The sequence repeats in the second diagram. In the third diagram, nodal treatment is active. An atrial pace is applied, then an atrial sense detected (this far field R wave is ignored in the AV delays), followed by a ventricular sense irrespective of far field R waves. The various cases illustrate that the nodal rhythm detection and treatment method will be effective for all possible sequences.
The preceding specific embodiments are illustrative of the practice of the invention. It is to be understood, therefore, that other expedients known to those skilled in the art or disclosed herein, may be employed without departing from the invention or the scope of the appended claims. For example, the present invention is not limited to a method of nodal rhythm detection and treatment. The present invention is also not limited to nodal rhythm detection and treatment algorithms per se, but may find further application as a means for detecting and treating nodal rhythm. The present invention further includes within its scope methods and systems for nodal rhythm detection and treatment as described above.
In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts a nail and a screw are equivalent structures.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5379776 | Murphy et al. | Jan 1995 | A |
| Number | Date | Country | |
|---|---|---|---|
| 20040210262 A1 | Oct 2004 | US |
