Method and device for switching between arrhythmia prevention modes

A device, such as an implantable cardiac device, and method for switching between arrhythmia prevention modes is disclosed. The method includes monitoring an electrocardiogram (EGM) of the heart, determining whether the heart is in a normal sinus rhythm or in an abnormal rhythm, delivering pacing pulses at a first rate to either an atrium or a ventricle when the heart is in a normal sinus rhythm, and delivering pacing pulses to a ventricle at a second rate when the heart is in an abnormal rhythm, such as an atrial arrhythmia. The first rate is selected to minimize the occurrence of premature ventricular contractions, and the second rate is selected to both minimize the occurrence of premature ventricular contractions and minimize the occurrence of premature conducted beats.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to implantable cardiac devices and, more particularly, to an implantable cardiac device with the capability of switching between arrhythmia prevention modes.

2. Background Art

An implantable cardiac device is a medical device that is implanted in a patient to monitor electrical activity of the heart and to deliver appropriate electrical and/or drug therapy, as required. Implantable cardiac devices include, for example, pacemakers, cardioverters and defibrillators. The term “implantable cardioverter defibrillator” or simply “ICD” is used herein to refer to any implantable cardiac device capable of delivering therapy to prevent or terminate a fast heart rate or a tachycardia. An ICD employs a battery to power its internal circuitry and to generate electrical therapy. The electrical therapy can include, for example, pacing pulses, cardioverting pulses and/or defibrillator pulses. This is in contrast to a “pacemaker” which is an implantable device specifically intended to treat slow heart rates or bradycardia.

An ICD also provides all the features of a pacemaker. However, a pacemaker does not provide all of the therapy that can be provided by an ICD. While the term “ICD” is used throughout the specification, it is to be understood that similar techniques as described herein can be applied in a pacemaker. A pacemaker cannot initiate therapy if a tachyarrhythmia occurs, but it can stabilize the ventricular rate in the setting of atrial fibrillation and can prevent atrial and ventricular arrhythmias.

There is indirect evidence that ventricular instability during an atrial arrhythmia can be a mechanism for inducing a ventricular arrhythmia. A recent study showed that the presence of atrial fibrillation is an independent predictor of appropriate ICD therapy, with ICD therapy being 1.8 times more frequent in patients in atrial fibrillation versus patients in sinus rhythm. More information regarding this study can be found in “Association Between Atrial Fibrillation and Appropriate Implantable Cardioverter Defibrillator Therapy: Results form a Prospective Study,” by Gronefeld, G, et al., Journal of Cardiovascular Electrophysiology, 11(11), pp. 1208-1214 (2000).

It has also been shown that overdrive ventricular pacing can reduce ventricular extrasystoles and arrhythmias. (See Pekarsky, V., et al., “Prevention Of Recurrent Life-Threatening Ventricular Arrythmias By Temporary Cardiac Pacing,” Acta Med Scand, Vol. 21, pp. 95-99 (1985).) In addition, it has been shown that pacing the ventricle slightly over the mean intrinsic ventricular rate during atrial fibrillation can significantly reduce the number of premature conducted beats (PCBs) from the atria. (See Wittkampf, F. and DeJongste, M., “Rate Stabilization By Right Ventricular Pacing in Patients with Atrial Fibrillation,” PACE, Vol. 9(Part II), pp. 1147-1153 (1986).)

What is needed is a device, such as an ICD, that takes advantage of such evidence to reduce the occurrence of arrhythmias by delivery of appropriate electrical therapy.

BRIEF SUMMARY OF THE INVENTION

For each individual patient, there is an optimum pacing rate that reduces premature ventricular contractions (PVCs) and also reduces the number of premature conducted beats (PCBs) from the atria during atrial arrhythmias. Conventional ICDs and related preventive therapy algorithms do not provide a pacing rate optimized for this purpose.

In patients with paroxysmal atrial fibrillation, there is a need for at least two modes of therapy. One therapy should be administered to the ventricle during atrial fibrillation to regularize and control the ventricular rhythm and possibly reduce ventricular ectopy, reducing the incidence of ventricular tachycardia or fibrillation. The other therapy should be provided during sinus rhythm to either the atrium or the ventricle to reduce ventricular and/or atrial extrasystoles, and potentially increase repolarization homogeneity. Further, various pacing algorithms might be utilized in the atrium to prevent atrial fibrillation and other atrial arrhythmias. Conventional ICDs and related preventive therapy algorithms do not provide this dual-mode form of prevention.

The present invention includes a device, such as an implantable cardiac device, and method for switching between arrhythmia prevention modes. The method includes monitoring the intrinsic signals inside the heart (i.e., the electrogram (EGM) of the heart), determining whether the heart is in a normal sinus rhythm or in an abnormal rhythm, delivering pacing pulses to either an atrium or a ventricle at a first rate when the heart is in a normal sinus rhythm, and delivering pacing pulses to a ventricle at a second rate when the heart is in an abnormal rhythm, such as an atrial arrhythmia. The advantage of this invention is that prevention therapy can be tailored to alleviate the symptoms and arrhythmia risk in both rhythm states. The invention, as described, involves two arrhythmia prevention modes. However, it will be appreciated by those skilled in the art that the invention can be extended to also cover three or more arrhythmia prevention modes. In addition, an arrhythmia prevention mode, depending on the underlying rhythm, may be applied to specific chambers of a heart (atrium or ventricle).

A method for pacing a heart for use in a pacing device such as an ICD with at least two pacing modes directed to reduce ventricular arrhythmias is presented, according to an embodiment of the present invention. The method includes monitoring an electrogram (EGM) of the heart, determining whether the heart is in a normal sinus rhythm or in an abnormal rhythm, delivering pacing pulses to either an atrium or a ventricle at a first rate when the heart is in a normal sinus rhythm, and delivering pacing pulses to a ventricle at a second rate when the heart is in an abnormal rhythm. In an embodiment of the present invention, the method further includes monitoring a response to the delivered pacing pulses with respect to a frequency of premature ventricular contractions (PVCs) and a frequency of premature conducted beats (PCBs).

According to an embodiment of the present invention, the pulses delivered at the first rate are delivered to an atrium, and the pulses delivered at the second rate are delivered to a ventricle. In another embodiment, the pulses delivered at the first rate are delivered to a ventricle, and the pulses delivered at the second rate are delivered to a ventricle. In a further embodiment, the pulses delivered at each rate are delivered to specified leads of a pacing device.

According to an embodiment of the present invention, the first rate and the second rate are determined from data obtained from the monitored EGM. In one embodiment, the first rate is selected to minimize the occurrence of premature ventricular contractions. The second rate is selected to both minimize the occurrence of premature ventricular contractions and minimize the occurrence of premature conducted beats.

According to an embodiment of the present invention, the method further includes continuing the monitoring of the EGM of the heart. This embodiment also includes adjusting the first rate to minimize premature ventricular contractions when delivering pacing pulses at the first rate. This embodiment further includes adjusting the second rate to minimize premature ventricular contractions and premature conducted beats when delivering pacing pulses at the second rate. In a further embodiment, a response to the adjusted rates is monitored with respect to a frequency of PVCs and a frequency of PCBs.

The embodiments of the present invention related to the device for switching between arrhythmia prevention modes include means for performing the above-described method.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description of the present invention refers to the accompanying drawings that illustrate exemplary embodiments consistent with this invention. Other embodiments are possible, and modifications may be made to the embodiments within the spirit and scope of the present invention. Therefore, the following detailed description is not meant to limit the invention. Rather, the scope of the invention is defined by the appended claims.

It will be apparent to one of skill in the art that the present invention, as described below, may be implemented in many different embodiments of hardware, software, firmware, and/or the entities illustrated in the figures. Any actual software and/or hardware described herein is not meant to limit the scope of the present invention. Thus, the structure, operation and behavior of the present invention will be described with the understanding that many modifications and variations of the embodiments are possible, given the level of detail presented herein.

Before describing the invention in detail, it is helpful to describe an example environment in which the invention may be implemented. The present invention is particularly useful in the environment of an implantable cardiac device. Implantable cardiac devices include, for example, pacemakers, cardioverters and defibrillators. The term “implantable cardioverter defibrillator” or simply “ICD” is used herein to refer to any implantable cardioverter defibrillator (“ICD”) or implantable cardiac device capable of delivering therapy to prevent, manage, or terminate a tachyarrhythmia in the atrium or ventricle.FIGS. 1A and 1Billustrate such an environment.

As shown inFIG. 1A, there is an exemplary ICD10in electrical communication with a patient's heart12by way of three leads,20,24and30, suitable for delivering multi-chamber stimulation and pacing therapy. To sense atrial cardiac signals and to provide right atrial chamber stimulation therapy, ICD10is coupled to implantable right atrial lead20having at least an atrial tip electrode22, which typically is implanted in the patient's right atrial appendage.

To sense left atrial and ventricular cardiac signals and to provide left-chamber pacing therapy, ICD10is coupled to “coronary sinus” lead24designed for placement in the “coronary sinus region” via the coronary sinus for positioning a distal electrode adjacent to the left ventricle and/or additional electrode(s) adjacent to the left atrium. As used herein, the phrase “coronary sinus region” refers to the vasculature of the left ventricle, including any portion of the coronary sinus, great cardiac vein, left marginal vein, left posterior ventricular vein, middle cardiac vein, and/or small cardiac vein or any other cardiac vein accessible by the coronary sinus.

Accordingly, exemplary coronary sinus lead24is designed to receive atrial and ventricular cardiac signals and to deliver left ventricular pacing therapy using at least a left ventricular tip electrode26, left atrial pacing therapy using at least a left atrial ring electrode27, and shocking therapy using at least a left atrial coil electrode28.

ICD10is also shown in electrical communication with the patient's heart12by way of an implantable right ventricular lead30having, in this embodiment, a right ventricular tip electrode32, a right ventricular ring electrode34, a right ventricular (RV) coil electrode36, and an SVC coil electrode38. Typically, right ventricular lead30is transvenously inserted into heart12so as to place the right ventricular tip electrode32in the right ventricular apex so that RV coil electrode36will be positioned in the right ventricle and SVC coil electrode38will be positioned in the superior vena cava. Accordingly, right ventricular lead30is capable of receiving cardiac signals and delivering stimulation in the form of pacing and shock therapy to the right ventricle.

FIG. 1Bshows a simplified block diagram of ICD10, which is capable of treating both fast and slow arrhythmias with stimulation therapy, including cardioversion, defibrillation, and pacing stimulation. While a particular multi-chamber device is shown, it is shown for illustration purposes only, and one of skill in the art could readily duplicate, eliminate or disable the appropriate circuitry in any desired combination to provide a device capable of treating the appropriate chamber(s) with the desired cardioversion, defibrillation and pacing stimulation.

A housing40of ICD10, shown schematically inFIG. 1B, is often referred to as the “can,” “case” or “case electrode” and may be programmably selected to act as the return electrode for all “unipolar” modes. Housing40may further be used as a return electrode alone or in combination with one or more of coil electrodes,28,36, and38for shocking purposes. Housing40further includes a connector (not shown) having a plurality of terminals,42,44,46,48,52,54,56, and58(shown schematically and, for convenience, the names of the electrodes to which they are connected are shown next to the terminals). As such, to achieve right atrial sensing and pacing, the connector includes at least a right atrial tip terminal (AR TIP)42adapted for connection to atrial tip electrode22.

To achieve left chamber sensing, pacing and shocking, the connector includes at least a left ventricular tip terminal (VL TIP)44, a left atrial ring terminal (AL RING)46, and a left atrial shocking terminal (AL COIL)48, which are adapted for connection to left ventricular electrode26, left atrial ring electrode27, and left atrial coil electrode28, respectively.

To support right chamber sensing, pacing, and shocking the connector also includes a right ventricular tip terminal (VR TIP)52, a right ventricular ring terminal (VR RING)54, a right ventricular shocking terminal (RV COIL)56, and an SVC shocking terminal (SVC COIL)58, which are configured for connection to right ventricular tip electrode32, right ventricular ring electrode34, RV coil electrode36, and SVC coil electrode38, respectively.

At the core of ICD10is a programmable microcontroller60which controls the various modes of stimulation therapy. As is well known in the art, microcontroller60typically includes a microprocessor, or equivalent control circuitry, designed specifically for controlling the delivery of stimulation therapy and can further include RAM or ROM memory, logic and timing circuitry, state machine circuitry, and I/O circuitry. Typically, microcontroller60includes the ability to process or monitor input signals (data) as controlled by a program code stored in a designated block of memory. The details of the design of microcontroller60are not critical to the present invention. Rather, any suitable microcontroller60can be used to carry out the functions described herein. The use of microprocessor-based control circuits for performing timing and data analysis functions are well known in the art. In specific embodiments of the present invention, microcontroller60performs some or all of the steps associated with the prevention therapy in accordance with the present invention.

Representative types of control circuitry that may be used with the invention include the microprocessor-based control system of U.S. Pat. No. 4,940,052 (Mann et al.) and the state-machines of U.S. Pat. Nos. 4,712,555 (Thornander et al.) and 4,944,298 (Sholder). For a more detailed description of the various timing intervals used within the ICDs and their inter-relationship, see U.S. Pat. No. 4,788,980 (Mann et al.). The '052, '555, '298 and '980 patents are incorporated herein by reference.

As shown inFIG. 1B, an atrial pulse generator70and a ventricular pulse generator72generate pacing stimulation pulses for delivery by right atrial lead20, right ventricular lead30, and/or coronary sinus lead24via an electrode configuration switch74. It is understood that in order to provide stimulation therapy in each of the four chambers of the heart, atrial and ventricular pulse generators70,72, may include dedicated, independent pulse generators, multiplexed pulse generators, or shared pulse generators. Pulse generators70and72are controlled by microcontroller60via appropriate control signals76and78, respectively, to trigger or inhibit the stimulation pulses.

Microcontroller60further includes timing control circuitry79which is used to control pacing parameters (e.g., the timing of stimulation pulses) as well as to keep track of the timing of refractory periods, PVARP intervals, noise detection windows, evoked response windows, alert intervals, marker channel timing, etc., which are well known in the art. Examples of pacing parameters include, but are not limited to, atrio-ventricular (AV) delay, interventricular (RV-LV) delay, atrial interconduction (A-A) delay, ventricular interconduction (V-V) delay, and pacing rate.

Switch74includes a plurality of switches for connecting the desired electrodes to the appropriate I/O circuits, thereby providing complete electrode programmability. Accordingly, switch74, in response to a control signal80from microcontroller60, determines the polarity of the stimulation pulses (e.g., unipolar, bipolar, combipolar, etc.) by selectively closing the appropriate combination of switches (not shown) as is known in the art.

Atrial sensing circuits82and ventricular sensing circuits84may also be selectively coupled to right atrial lead20, coronary sinus lead24, and right ventricular lead30, through switch74for detecting the presence of cardiac activity in each of the four chambers of the heart. Accordingly, the atrial (ATR. SENSE) and ventricular (VTR. SENSE) sensing circuits82and84may include dedicated sense amplifiers, multiplexed amplifiers, or shared amplifiers. Switch74determines the “sensing polarity” of the cardiac signal by selectively closing the appropriate switches, as is also known in the art. In this way, the clinician may program the sensing polarity independent of the stimulation polarity.

Each sensing circuit,82and84, preferably employs one or more low power, precision amplifiers with programmable gain and/or automatic sensitivity control, bandpass filtering, and a threshold detection circuit, as known in the art, to selectively sense the cardiac signal of interest. The automatic sensitivity control (ASC) enables ICD10to deal effectively with the difficult problem of sensing the low amplitude signal characteristics of atrial or ventricular fibrillation. Such sensing circuits,82and84, can be used to determine cardiac performance values used in the present invention.

The outputs of atrial and ventricular sensing circuits82and84are connected to microcontroller60which, in turn, are able to trigger or inhibit atrial and ventricular pulse generators,70and72, respectively, in a demand fashion in response to the absence or presence of cardiac activity, in the appropriate chambers of the heart. Sensing circuits82and84, in turn, receive control signals over signal lines86and88from microcontroller60for purposes of measuring cardiac performance at appropriate times, and for controlling the gain, threshold, polarization charge removal circuitry (not shown), and timing of any blocking circuitry (not shown) coupled to the inputs of sensing circuits82and84.

For arrhythmia detection, ICD10utilizes the atrial and ventricular sensing circuits82and84to sense cardiac signals to determine whether a rhythm is physiologic or pathologic. The timing intervals between sensed events (e.g., P-waves, R-waves, and depolarization signals associated with fibrillation which are sometimes referred to as “F-waves” or “Fib-waves”) are then classified by microcontroller60by comparing them to a predefined rate zone limit (i.e., bradycardia, normal, low rate VT, high rate VT, and fibrillation rate zones) and various other characteristics (e.g., sudden onset, stability, physiologic sensors, and morphology, etc.) in order to determine the type of remedial therapy that is needed (e.g., bradycardia pacing, anti-tachycardia pacing, cardioversion shocks or defibrillation shocks, collectively referred to as “tiered therapy”).

Microcontroller60utilizes arrhythmia detection circuitry75and morphology detection circuitry77to recognize and classify arrhythmia so that appropriate therapy can be delivered.

Cardiac signals are also applied to the inputs of an analog-to-digital (A/D) data acquisition system90. Data acquisition system90is configured to acquire intracardiac electrogram signals, convert the raw analog data into a digital signal, and store the digital signals for later processing and/or telemetric transmission to an external device102. Data acquisition system90is coupled to right atrial lead20, coronary sinus lead24, and right ventricular lead30through switch74to sample cardiac signals across any pair of desired electrodes.

Advantageously, data acquisition system90can be coupled to microcontroller60, or other detection circuitry, for detecting an evoked response from heart12in response to an applied stimulus, thereby aiding in the detection of “capture.” Capture occurs when an electrical stimulus applied to the heart is of sufficient energy to depolarize the cardiac tissue, thereby causing the heart muscle to contract. Microcontroller60detects a depolarization signal during a window following a stimulation pulse, the presence of which indicates that capture has occurred. Microcontroller60enables capture detection by triggering ventricular pulse generator72to generate a stimulation pulse, starting a capture detection window using timing control circuitry79within microcontroller60, and enabling data acquisition system90via control signal92to sample the cardiac signal that falls in the capture detection window and, based on the amplitude, determines if capture has occurred.

The implementation of capture detection circuitry and algorithms are well known. See for example, U.S. Pat. No. 4,729,376 (DeCote, Jr.); U.S. Pat. No. 4,708,142 (DeCote, Jr.); U.S. Pat. No. 4,686,988 (Sholder); U.S. Pat. No. 4,969,467 (Callaghan et al.); and U.S. Pat. No. 5,350,410 (Kleks et al.), which patents are hereby incorporated herein by reference. The type of capture detection system used is not critical to the present invention.

Microcontroller60is further coupled to a memory94by a suitable data/address bus96, wherein the programmable operating parameters used by microcontroller60are stored and modified, as required, in order to customize the operation of ICD10to suit the needs of a particular patient. Such operating parameters define, for example, pacing pulse amplitude, pulse duration, electrode polarity, rate, sensitivity, automatic features, arrhythmia detection criteria, and the amplitude, waveshape and vector of each shocking pulse to be delivered to the patient's heart12within each respective tier of therapy.

Advantageously, the operating parameters of ICD10may be non-invasively programmed into memory94through a telemetry circuit100in telemetric communication with external device102, such as a programmer, transtelephonic transceiver, or a diagnostic system analyzer. Telemetry circuit100is activated by microcontroller60by a control signal106. Telemetry circuit100advantageously allows intracardiac electrograms and status information relating to the operation of ICD10(as contained in microcontroller60or memory94) to be sent to external device102through an established communication link104.

For examples of such devices, see U.S. Pat. No. 4,809,697, entitled “Interactive Programming and Diagnostic System for use with Implantable Pacemaker” (Causey, III et al.); U.S. Pat. No. 4,944,299, entitled “High Speed Digital Telemetry System for Implantable Device” (Silvian); and U.S. Pat. No. 6,275,734, entitled “Efficient Generation of Sensing Signals in an Implantable Medical Device such as a Pacemaker or ICD” (McClure et al.), which patents are hereby incorporated herein by reference.

In an embodiment, ICD10further includes a physiologic sensor108that can be used to detect changes in cardiac performance or changes in the physiological condition of the heart. Accordingly, microcontroller60can respond by adjusting the various pacing parameters (such as rate, AV Delay, RV-LV Delay, V-V Delay, etc.) in accordance with the embodiments of the present invention. Microcontroller60controls adjustments of pacing parameters by, for example, controlling the stimulation pulses generated by the atrial and ventricular pulse generators70and72. While shown as being included within ICD10, it is to be understood that physiologic sensor108may also be external to ICD10, yet still be implanted within or carried by the patient. More specifically, sensor108can be located inside ICD10, on the surface of ICD10, in a header of ICD10, or on a lead (which can be placed inside or outside the bloodstream).

ICD10additionally includes a battery110which provides operating power to all of the circuits shown inFIG. 1B. For ICD10, which employs shocking therapy, battery110must be capable of operating at low current drains for long periods of time, and then be capable of providing high-current pulses (for capacitor charging) when the patient requires a shock pulse. Battery110must also have a predictable discharge characteristic so that elective replacement time can be detected. Accordingly, ICD10preferably employs lithium/silver vanadium oxide batteries, as is true for most (if not all) current devices. ICD10further includes a battery charge indicator circuit160. Battery charge indicator circuit160monitors current drawn from battery110to improve prediction of when battery110needs replacement.

ICD10further includes magnet detection circuitry (not shown), coupled to microcontroller60. It is the purpose of the magnet detection circuitry to detect when a magnet is placed over ICD10, which magnet may be used by a clinician to perform various test functions of ICD10and/or to signal microcontroller60that the external programmer102is in place to receive or transmit data to microcontroller60through telemetry circuit100.

As further shown inFIG. 1B, ICD10is shown as having an impedance measuring circuit112which is enabled by microcontroller60via a control signal114. The known uses for an impedance measuring circuit112include, but are not limited to, lead impedance surveillance during the acute and chronic phases for proper lead positioning or dislodgement; detecting operable electrodes and automatically switching to an operable pair if dislodgement occurs; measuring respiration or minute ventilation; measuring thoracic impedance for determining shock thresholds; detecting when the device has been implanted; measuring stroke volume; and detecting the opening of heart valves, etc. The impedance measuring circuit112is advantageously coupled to switch74so that any desired electrode may be used. The impedance measuring circuit112is not critical to the present invention and is shown only for completeness.

In the case where ICD10is intended to operate as a cardioverter, pacer or defibrillator, it must detect the occurrence of an arrhythmia and automatically apply an appropriate electrical therapy to the heart aimed at terminating the detected arrhythmia. To this end, microcontroller60further controls a shocking circuit116by way of a control signal118. The shocking circuit116generates shocking pulses of low (up to about 0.5 Joules), moderate (about 0.5-10 Joules), or high energy (about 11 to 40 Joules), as controlled by microcontroller60. Such shocking pulses are applied to the patient's heart12through at least two shocking electrodes (e.g., selected from left atrial coil electrode28, RV coil electrode36, and SVC coil electrode38). As noted above, housing40may act as an active electrode in combination with RV electrode36, or as part of a split electrical vector using SVC coil electrode38or left atrial coil electrode28(i.e., using the RV electrode as a common electrode).

With the description of an example environment, such as an ICD, in mind, features of the present invention are described in more detail below.

As stated in the Background section, there is indirect evidence that ventricular instability during an atrial arrhythmia can be a mechanism for inducing a ventricular arrhythmia. As also stated in the Background section, it has also been shown that overdrive ventricular pacing can reduce ventricular extrasystoles and arrhythmias. In addition, it has been shown that pacing the ventricle slightly over the mean intrinsic ventricular rate during atrial fibrillation can significantly reduce the number of premature conducted beats (PCBs) from the atria.

There is an optimum pacing rate that reduces premature ventricular contractions (PVCs) and also reduces the number of premature conducted beats (PCBs) from the atria during atrial arrhythmias. In patients with paroxysmal atrial fibrillation, there is a need for at least two modes of preventive therapy. One therapy should be administered to the ventricle during atrial fibrillation to regularize the ventricular rhythm and possibly reduce ventricular ectopy. Another therapy should be provided during sinus rhythm to either the atrium or the ventricle to reduce atrial or ventricular extrasystoles respectively, and potentially increase repolarization homogeneity of the respective chamber. Further, various pacing algorithms might be utilized in the atrium to prevent atrial fibrillation and other atrial arrhythmias.

With the background in mind, a method of pacing for use in a pacing device such as an ICD with at least two pacing modes directed to reduce ventricular arrhythmias will now be described, according to an embodiment of the present invention. For example, one pacing mode is to be used during a normal sinus rhythm, and another pacing mode is to be used during an abnormal rhythm, such as an atrial arrhythmia. Optimum pacing rates for use during each mode are calculated. The prevention therapy is tailored to alleviate symptoms and other arrhythmia risk in both rhythm states.

There are many ways that a multi-mode system such as this can be implemented. In addition, there are many possible feedback parameters that can be used to control the output of a pacing device. The feedback parameters and how they are used to control device output are dependent on which mode the device is currently in (e.g., a normal sinus mode, or an abnormal arrhythmia mode). For example, possible feedback parameters include, but are not limited to, the number of PCBs from the atria, the mean ventricular rate during atrial fibrillation, PVCs (including frequency, QRS morphology being either from a single focus (monomorphic) or from multiple foci (polymorphic) occurrence, and repetitive cycles such as doublet and triplet occurrence), and cardiac output.

Based on feedback parameters, possible prevention therapy outputs include, but are not limited to, vagal stimulation and pacing at a physiologic rate. Pacing at a preventive rate may be slightly above the intrinsic heart rate, for example, and may be accomplished at the septum or at multiple ventricular sites, for example. In patients with chronic or paroxysmal atrial fibrillation, without heart failure or increased R wave width, the pacing may be at a unique location such as the interventricular septum to minimize the detrimental effects that are being recognized with RV apical pacing. In patients with heart failure or increased R wave width, it may be beneficial to pace biventricularly. The site of stimulation is dependent on where the leads are placed at the time of implantation. With multisite stimulation and total independent control of each lead, it may be possible to designate to which lead or leads the output should be delivered in order to achieve preventive therapy.

According to embodiments of the present invention, the number of PCBs and the number of PVCs are used as feedback for pacing rate optimization during normal sinus rhythm and during an abnormal rhythm, such as atrial fibrillation. This embodiment is described in more detail below with reference to the accompanying figures. Note that, according to embodiments of the present invention, the number of PVCs is also used as a tripper to initiate or turn on pacing.

FIGS. 2A,2B, and2C illustrate example pacing rate data used in accordance with the invention to determine preferred or optimal pacing rates to be used during normal sinus rhythm and during abnormal rhythm (such as atrial fibrillation), according to an embodiment of the present invention. The invention uses feedback parameters such as heartbeats per minute, number of PVCs, and number of PCBs to determine a preferred or optimal pacing rate for a particular condition. For example,FIG. 2Adepicts a function plot250of PVC risk versus pacing rate (in beats per minute). While the heart has a normal sinus rhythm, the optimum atrial pacing rate is selected based on minimizing the risk of PVCs. Based on function plot250, the optimal pacing rate during a normal sinus rhythm is depicted as rate251.

FIG. 2Bdepicts a function plot252of PCB frequency versus pacing rate (in beats per minute).FIG. 2Cdepicts, on the same graph, function plots250and252, as well as a resultant function plot254. The resultant function plot254is the sum of function plots250and252. The minimum point on resultant function plot254is selected as the optimum pacing rate during an abnormal rhythm, such as atrial fibrillation. Therefore, according toFIG. 2C, the optimum pacing rate during an abnormal rhythm is depicted as rate256.

A patient is expected to have a changing substrate (i.e., changing condition of the heart), such as the development of myocardial infarction or acute ischemia. This changing substrate may lead to an increased number of PVCs or PCBs. Therefore, the data for function plots250,252, and254must be updated on a regular basis to keep the optimum pacing rates current.

In this example embodiment, the optimum pacing rate during an abnormal rhythm, such as atrial fibrillation, is the pacing rate that minimizes both the PVC and PCB risk. It will be appreciated by those skilled in the art, however, that minimizing both the PVC and PCB risk may be accomplished via other methods besides summing function plots250and252.

A method300of pacing with two arrhythmia prevention modes in accordance with the invention is illustrated inFIG. 3. According to an embodiment of the present invention, the method300begins at step358, in which an EGM of the heart is monitored. Step358is a learning phase that will allow the creation of databases, data arrays, data plots or functions, such as function plots250,252, and254described above, for example. For function plots250,252, and254, the level of PVC risk and the frequency of PCBs are measured as functions of a pacing rate (such as beats per minute (bpm)). The pacing rates tested are from a mean intrinsic rate (e.g., 70 bpm) up to a physiologically acceptable over-drive rate (e.g., 140 bpm), for example.

In step359, it is determined whether the heart is currently in a normal sinus rhythm or in an abnormal rhythm such as an atrial fibrillation or an already present atrial tachyarrhythmia. In step360, a first heart rate is determined, such as the optimum heart rate for use during a normal sinus rhythm, for example. In one embodiment, step360is accomplished by selecting a heart rate to minimize the occurrence of PVCs, as shown in step476ofFIG. 4A. In the presence of normal sinus rhythm, the optimum heart rate may be associated with atrial pacing, AV sequential pacing, or ventricular pacing. Referring again toFIG. 3, in step362, a second heart rate is determined, such as the optimum heart rate for use during an abnormal rhythm (atrial fibrillation, for example). In one embodiment, step362is accomplished by selecting a heart rate to minimize the occurrence of both PVCs and PCBs, as shown in step478ofFIG. 4B.

Depending on whether the heart has a normal sinus rhythm or an abnormal rhythm, such as an atrial arrhythmia, the next step is either step364or step366. If the heart has a normal sinus rhythm, paces are delivered at the first rate in step364. According to an embodiment of the present invention, the paces at the first rate are delivered to an atrium. In another embodiment, the paces at the first rate are delivered to a ventricle. In a further embodiment, the paces at the first rate are delivered to a specified lead of a pacing device. If the heart has an abnormal rhythm, paces are delivered at the second rate in step366. According to an embodiment of the present invention, the paces at the second rate are delivered to a ventricle. In another embodiment, the paces at the second rate are delivered to a specified lead of a pacing device. Step367follows both steps364and366. In step367, a response to the delivered pacing pulses is monitored with respect to the frequency of PVCs and the frequency of PCBs. In step368, monitoring the EGM of the heart is continued.

The data functions initially determined in step358are preferably updated as monitored EGM data changes. The updated data is then used to adjust the heart rates determined in steps360and/or362. Depending on whether the first rate or the second rate is being used, the next step is either step370or step372. If the first rate is being used, the first rate is adjusted based on monitored EGM data changes in step370. According to an embodiment of the present invention, the adjustment of the first rate includes re-determining the first rate and delivering pacing pulses at the re-determined first rate. In one embodiment, the first rate is determined by selecting a heart rate to minimize the occurrence of PVCs, as was determined in step476ofFIG. 4A. If the second rate is being used, the second rate is adjusted based on monitored EGM data changes in step372. According to an embodiment of the present invention, the adjustment of the second rate includes re-determining the second rate and delivering pacing pulses at the re-determined second rate. In one embodiment, the second rate is determined by selecting a heart rate to minimize the occurrence of both PVCs and PCBs, as was determined in step478ofFIG. 4B.

Step373follows both steps370and372. In step373, a response to the adjusted pacing pulses is monitored with respect to the frequency of PVCs and the frequency of PCBs. In step374, it is determined whether the heart has a normal sinus rhythm or an abnormal rhythm, such as an atrial fibrillation. If the heart has a normal sinus rhythm, the method continues at step364. If the heart has an abnormal rhythm, the method continues at step366. Thus, in the manner described, the invention monitors an EGM and switches between an arrhythmia prevention mode associated with sinus rhythm and an arrhythmia prevention mode associated with an abnormal rhythm, so that pacing occurs at the optimum rate for the current mode.

A method500of pacing with two arrhythmia prevention modes, according to an embodiment of the present invention, is illustrated inFIG. 5. The method500begins at step580, in which a PVC versus pacing rate function and a PCB versus pacing rate function are initialized during a learning period in which a heart's EGM is Monitored. In step582, an optimum pacing rate for use during sinus rhythm is determined using the PVC versus pacing rate function by determining the minimum point of the function. In sinus rhythm, while it is helpful to overdrive suppress PVCs, it is also helpful to suppress atrial premature complexes (APCs) in an effort to prevent atrial fibrillation. For more information on atrial fibrillation suppression, see U.S. Pat. No. 6,519,493 to Florio et al., which is incorporated herein by reference. In step584, an optimum pacing rate for use during an abnormal rhythm, such as atrial fibrillation, is determined by adding the PVC versus pacing rate function and the PCB versus pacing rate function, and determining the minimum point of the resultant function.

In step586, the mode of the prevention therapy is determined depending on the current arrhythmia state (i.e., sinus rhythm or abnormal rhythm). The appropriate pacing rate determined in step582or step584is used depending on the mode. In step588, the heart's EGM is monitored. During heart monitoring, feedback parameters, such as the frequency of PVCs and PCBs, are collected and used to make pacing decisions.

During monitoring step588, if the current mode is the arrhythmia prevention mode associated with sinus rhythm, but an abnormal arrhythmia is detected (such as atrial fibrillation or other atrial tachyarrhythmia), the method proceeds to step590. In step590, the mode is switched from the arrhythmia prevention mode associated with sinus rhythm to the ventricular arrhythmia prevention mode associated with an abnormal rhythm, and the pacing rate is adjusted accordingly. The method then returns to step588, during which the heart's EGM is again monitored.

During monitoring step588, if the current mode is the ventricular arrhythmia prevention mode associated with an abnormal rhythm, but a sinus rhythm is detected, the method proceeds to step592. In step592, the mode is switched from the ventricular arrhythmia prevention mode associated with an abnormal rhythm to the arrhythmia prevention mode associated with sinus rhythm, and the pacing rate is adjusted accordingly. The method then returns to step588, during which the heart's EGM is again monitored.

During monitoring step588, if the frequency of PVCs or PCBs crosses a predetermined threshold, the method proceeds to step594. In step594, the current arrhythmia prevention mode is determined. If the current arrhythmia prevention mode is the mode associated with sinus rhythm, the method proceeds to step597. In step597, the pacing rate is adjusted to minimize PVCs. If the current arrhythmia prevention mode is the mode associated with an abnormal rhythm, the method proceeds to step596. In step596, the pacing rate is adjusted to minimize both PVCs and PCBs. In both steps596and597, the adjustment of the pacing rate begins with the stepping down of the pacing rate, according to an embodiment of the present invention. After steps596and597, the method continues at step598. In step598, it is determined whether the pacing rate adjustment of step596or597was successful. If it was not successful, the method returns to step580to re-initialize the PVC versus pacing rate function and the PCB versus pacing rate function during a learning period in which the heart's EGM is monitored. If in step598the pacing rate adjustment is determined successful, the method proceeds to step599. In step599, the adjusted rate is held. In one embodiment, the method may optionally return to step580to schedule a new learning period to re-optimize the pacing rates. In another embodiment, the method may optionally return to step588to continue monitoring.

Further information regarding preventive stimulation to prevent tachyarrhythmias can be found in U.S. Pat. No. 6,058,328 to Levine et al. and U.S. Pat. No. 6,292,694 to Schloss et al. The '328 and '694 patents are incorporated herein by reference.

It will be appreciated by those skilled in the art that the above methods300and500can be used within the hardware, software, and/or firmware of a pacing system, such as the ICD described earlier with reference toFIGS. 1A and 1B, for example.